diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index ad67596360..8d7f76cb0a 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -4,6 +4,7 @@ on:
   push:
     branches:
       - master
+      - 0.12.x
 concurrency:
   # Cancels pending runs when a PR gets updated.
   group: ${{ github.head_ref || github.run_id }}-${{ github.actor }}
diff --git a/CMakeLists.txt b/CMakeLists.txt
index e677ee0947..8a409096e3 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -37,7 +37,7 @@ set(CMAKE_MODULE_PATH ${CMAKE_SOURCE_DIR}/cmake ${CMAKE_MODULE_PATH})
 
 set(ZIG_VERSION_MAJOR 0)
 set(ZIG_VERSION_MINOR 12)
-set(ZIG_VERSION_PATCH 0)
+set(ZIG_VERSION_PATCH 1)
 set(ZIG_VERSION "" CACHE STRING "Override Zig version string. Default is to find out with git.")
 
 if("${ZIG_VERSION}" STREQUAL "")
@@ -92,6 +92,12 @@ set(ZIG_SHARED_LLVM off CACHE BOOL "Prefer linking against shared LLVM libraries
 set(ZIG_STATIC_LLVM ${ZIG_STATIC} CACHE BOOL "Prefer linking against static LLVM libraries")
 set(ZIG_STATIC_ZLIB ${ZIG_STATIC} CACHE BOOL "Prefer linking against static zlib")
 set(ZIG_STATIC_ZSTD ${ZIG_STATIC} CACHE BOOL "Prefer linking against static zstd")
+if(APPLE AND ZIG_STATIC)
+  set(ZIG_STATIC_CURSES on)
+else()
+  set(ZIG_STATIC_CURSES off)
+endif()
+set(ZIG_STATIC_CURSES ${ZIG_STATIC_CURSES} CACHE BOOL "Prefer linking against static curses")
 set(ZIG_USE_CCACHE off CACHE BOOL "Use ccache")
 
 if(ZIG_USE_CCACHE)
@@ -160,7 +166,7 @@ if(ZIG_STATIC_ZSTD)
     list(APPEND LLVM_LIBRARIES "${ZSTD}")
 endif()
 
-if(APPLE AND ZIG_STATIC)
+if(ZIG_STATIC_CURSES)
     list(REMOVE_ITEM LLVM_LIBRARIES "-lcurses")
     find_library(CURSES NAMES libcurses.a libncurses.a NAMES_PER_DIR
       PATHS
diff --git a/README.md b/README.md
index 13214b5bed..c069ed0387 100644
--- a/README.md
+++ b/README.md
@@ -85,8 +85,6 @@ therefore lacking these features:
 - [Some ELF linking features](https://github.com/ziglang/zig/issues/17749)
 - [Most COFF/PE linking features](https://github.com/ziglang/zig/issues/17751)
 - [Some WebAssembly linking features](https://github.com/ziglang/zig/issues/17750)
-- [Ability to output LLVM bitcode](https://github.com/ziglang/zig/issues/13265)
-- [Windows resource file compilation](https://github.com/ziglang/zig/issues/17752)
 - [Ability to create import libs from def files](https://github.com/ziglang/zig/issues/17807)
 - [Automatic importlib file generation for Windows DLLs](https://github.com/ziglang/zig/issues/17753)
 - [Ability to create static archives from object files](https://github.com/ziglang/zig/issues/9828)
diff --git a/build.zig b/build.zig
index 0e43b82f9a..b5db6e7a5b 100644
--- a/build.zig
+++ b/build.zig
@@ -9,7 +9,7 @@ const fs = std.fs;
 const InstallDirectoryOptions = std.Build.InstallDirectoryOptions;
 const assert = std.debug.assert;
 
-const zig_version = std.SemanticVersion{ .major = 0, .minor = 12, .patch = 0 };
+const zig_version = std.SemanticVersion{ .major = 0, .minor = 12, .patch = 1 };
 const stack_size = 32 * 1024 * 1024;
 
 pub fn build(b: *std.Build) !void {
diff --git a/doc/build.zig.zon.md b/doc/build.zig.zon.md
index de5ec5fe9c..d0740a9237 100644
--- a/doc/build.zig.zon.md
+++ b/doc/build.zig.zon.md
@@ -12,6 +12,14 @@ build.zig.
 
 String. Required.
 
+This is the default name used by packages depending on this one. For example,
+when a user runs `zig fetch --save <url>`, this field is used as the key in the
+`dependencies` table. Although the user can choose a different name, most users
+will stick with this provided value.
+
+It is redundant to include "zig" in this name because it is already within the
+Zig package namespace.
+
 ### `version`
 
 String. Required.
diff --git a/doc/langref.html.in b/doc/langref.html.in
index 2a53d40b4c..32be79988c 100644
--- a/doc/langref.html.in
+++ b/doc/langref.html.in
@@ -314,8 +314,8 @@
           <a href="https://ziglang.org/documentation/0.9.1/">0.9.1</a> |
           <a href="https://ziglang.org/documentation/0.10.1/">0.10.1</a> |
           <a href="https://ziglang.org/documentation/0.11.0/">0.11.0</a> |
-          <a href="https://ziglang.org/documentation/0.12.0/">0.12.0</a> |
-          master
+          0.12.1 |
+          <a href="https://ziglang.org/documentation/master/">master</a>
         </nav>
         <nav aria-labelledby="table-of-contents">
           <h2 id="table-of-contents">Table of Contents</h2>
@@ -9040,7 +9040,7 @@ test "integer cast panic" {
       {#header_close#}
 
       {#header_open|@wasmMemorySize#}
-      <pre>{#syntax#}@wasmMemorySize(index: u32) u32{#endsyntax#}</pre>
+      <pre>{#syntax#}@wasmMemorySize(index: u32) usize{#endsyntax#}</pre>
       <p>
       This function returns the size of the Wasm memory identified by {#syntax#}index{#endsyntax#} as
       an unsigned value in units of Wasm pages. Note that each Wasm page is 64KB in size.
@@ -9054,7 +9054,7 @@ test "integer cast panic" {
       {#header_close#}
 
       {#header_open|@wasmMemoryGrow#}
-      <pre>{#syntax#}@wasmMemoryGrow(index: u32, delta: u32) i32{#endsyntax#}</pre>
+      <pre>{#syntax#}@wasmMemoryGrow(index: u32, delta: usize) isize{#endsyntax#}</pre>
       <p>
       This function increases the size of the Wasm memory identified by {#syntax#}index{#endsyntax#} by
       {#syntax#}delta{#endsyntax#} in units of unsigned number of Wasm pages. Note that each Wasm page
diff --git a/lib/compiler/std-docs.zig b/lib/compiler/std-docs.zig
index e6240a3c70..4642b4317f 100644
--- a/lib/compiler/std-docs.zig
+++ b/lib/compiler/std-docs.zig
@@ -117,6 +117,7 @@ const Context = struct {
 
 fn serveRequest(request: *std.http.Server.Request, context: *Context) !void {
     if (std.mem.eql(u8, request.head.target, "/") or
+        std.mem.eql(u8, request.head.target, "/debug") or
         std.mem.eql(u8, request.head.target, "/debug/"))
     {
         try serveDocsFile(request, context, "docs/index.html", "text/html");
@@ -433,6 +434,7 @@ fn openBrowserTab(gpa: Allocator, url: []const u8) !void {
 fn openBrowserTabThread(gpa: Allocator, url: []const u8) !void {
     const main_exe = switch (builtin.os.tag) {
         .windows => "explorer",
+        .macos => "open",
         else => "xdg-open",
     };
     var child = std.ChildProcess.init(&.{ main_exe, url }, gpa);
diff --git a/lib/init/build.zig.zon b/lib/init/build.zig.zon
index 50da5587b1..8684a901a9 100644
--- a/lib/init/build.zig.zon
+++ b/lib/init/build.zig.zon
@@ -1,5 +1,13 @@
 .{
+    // This is the default name used by packages depending on this one. For
+    // example, when a user runs `zig fetch --save <url>`, this field is used
+    // as the key in the `dependencies` table. Although the user can choose a
+    // different name, most users will stick with this provided value.
+    //
+    // It is redundant to include "zig" in this name because it is already
+    // within the Zig package namespace.
     .name = "$",
+
     // This is a [Semantic Version](https://semver.org/).
     // In a future version of Zig it will be used for package deduplication.
     .version = "0.0.0",
@@ -47,20 +55,17 @@
 
     // Specifies the set of files and directories that are included in this package.
     // Only files and directories listed here are included in the `hash` that
-    // is computed for this package.
+    // is computed for this package. Only files listed here will remain on disk
+    // when using the zig package manager. As a rule of thumb, one should list
+    // files required for compilation plus any license(s).
     // Paths are relative to the build root. Use the empty string (`""`) to refer to
     // the build root itself.
     // A directory listed here means that all files within, recursively, are included.
     .paths = .{
-        // This makes *all* files, recursively, included in this package. It is generally
-        // better to explicitly list the files and directories instead, to insure that
-        // fetching from tarballs, file system paths, and version control all result
-        // in the same contents hash.
-        "",
+        "build.zig",
+        "build.zig.zon",
+        "src",
         // For example...
-        //"build.zig",
-        //"build.zig.zon",
-        //"src",
         //"LICENSE",
         //"README.md",
     },
diff --git a/lib/std/Build/Module.zig b/lib/std/Build/Module.zig
index d19f0a781e..a142bbd405 100644
--- a/lib/std/Build/Module.zig
+++ b/lib/std/Build/Module.zig
@@ -110,11 +110,18 @@ pub const RcSourceFile = struct {
     ///  /x (ignore the INCLUDE environment variable)
     ///  /D_DEBUG or /DNDEBUG depending on the optimization mode
     flags: []const []const u8 = &.{},
+    /// Include paths that may or may not exist yet and therefore need to be
+    /// specified as a LazyPath. Each path will be appended to the flags
+    /// as `/I <resolved path>`.
+    include_paths: []const LazyPath = &.{},
 
     pub fn dupe(self: RcSourceFile, b: *std.Build) RcSourceFile {
+        const include_paths = b.allocator.alloc(LazyPath, self.include_paths.len) catch @panic("OOM");
+        for (include_paths, self.include_paths) |*dest, lazy_path| dest.* = lazy_path.dupe(b);
         return .{
             .file = self.file.dupe(b),
             .flags = b.dupeStrings(self.flags),
+            .include_paths = include_paths,
         };
     }
 };
@@ -503,6 +510,9 @@ pub fn addWin32ResourceFile(m: *Module, source: RcSourceFile) void {
     rc_source_file.* = source.dupe(b);
     m.link_objects.append(allocator, .{ .win32_resource_file = rc_source_file }) catch @panic("OOM");
     addLazyPathDependenciesOnly(m, source.file);
+    for (source.include_paths) |include_path| {
+        addLazyPathDependenciesOnly(m, include_path);
+    }
 }
 
 pub fn addAssemblyFile(m: *Module, source: LazyPath) void {
diff --git a/lib/std/Build/Step/CheckObject.zig b/lib/std/Build/Step/CheckObject.zig
index f8f0fcd584..1c2e297bb3 100644
--- a/lib/std/Build/Step/CheckObject.zig
+++ b/lib/std/Build/Step/CheckObject.zig
@@ -2475,12 +2475,12 @@ const WasmDumper = struct {
                     try writer.print("params {d}\n", .{params});
                     var index: u32 = 0;
                     while (index < params) : (index += 1) {
-                        try parseDumpType(step, std.wasm.Valtype, reader, writer);
+                        _ = try parseDumpType(step, std.wasm.Valtype, reader, writer);
                     } else index = 0;
                     const returns = try std.leb.readULEB128(u32, reader);
                     try writer.print("returns {d}\n", .{returns});
                     while (index < returns) : (index += 1) {
-                        try parseDumpType(step, std.wasm.Valtype, reader, writer);
+                        _ = try parseDumpType(step, std.wasm.Valtype, reader, writer);
                     }
                 }
             },
@@ -2512,11 +2512,11 @@ const WasmDumper = struct {
                             try parseDumpLimits(reader, writer);
                         },
                         .global => {
-                            try parseDumpType(step, std.wasm.Valtype, reader, writer);
+                            _ = try parseDumpType(step, std.wasm.Valtype, reader, writer);
                             try writer.print("mutable {}\n", .{0x01 == try std.leb.readULEB128(u32, reader)});
                         },
                         .table => {
-                            try parseDumpType(step, std.wasm.RefType, reader, writer);
+                            _ = try parseDumpType(step, std.wasm.RefType, reader, writer);
                             try parseDumpLimits(reader, writer);
                         },
                     }
@@ -2531,7 +2531,7 @@ const WasmDumper = struct {
             .table => {
                 var i: u32 = 0;
                 while (i < entries) : (i += 1) {
-                    try parseDumpType(step, std.wasm.RefType, reader, writer);
+                    _ = try parseDumpType(step, std.wasm.RefType, reader, writer);
                     try parseDumpLimits(reader, writer);
                 }
             },
@@ -2544,7 +2544,7 @@ const WasmDumper = struct {
             .global => {
                 var i: u32 = 0;
                 while (i < entries) : (i += 1) {
-                    try parseDumpType(step, std.wasm.Valtype, reader, writer);
+                    _ = try parseDumpType(step, std.wasm.Valtype, reader, writer);
                     try writer.print("mutable {}\n", .{0x01 == try std.leb.readULEB128(u1, reader)});
                     try parseDumpInit(step, reader, writer);
                 }
@@ -2605,12 +2605,13 @@ const WasmDumper = struct {
         }
     }
 
-    fn parseDumpType(step: *Step, comptime WasmType: type, reader: anytype, writer: anytype) !void {
-        const type_byte = try reader.readByte();
-        const valtype = std.meta.intToEnum(WasmType, type_byte) catch {
-            return step.fail("Invalid wasm type value '{d}'", .{type_byte});
+    fn parseDumpType(step: *Step, comptime E: type, reader: anytype, writer: anytype) !E {
+        const byte = try reader.readByte();
+        const tag = std.meta.intToEnum(E, byte) catch {
+            return step.fail("invalid wasm type value '{d}'", .{byte});
         };
-        try writer.print("type {s}\n", .{@tagName(valtype)});
+        try writer.print("type {s}\n", .{@tagName(tag)});
+        return tag;
     }
 
     fn parseDumpLimits(reader: anytype, writer: anytype) !void {
@@ -2642,29 +2643,54 @@ const WasmDumper = struct {
         }
     }
 
+    /// https://webassembly.github.io/spec/core/appendix/custom.html
     fn parseDumpNames(step: *Step, reader: anytype, writer: anytype, data: []const u8) !void {
         while (reader.context.pos < data.len) {
-            try parseDumpType(step, std.wasm.NameSubsection, reader, writer);
-            const size = try std.leb.readULEB128(u32, reader);
-            const entries = try std.leb.readULEB128(u32, reader);
-            try writer.print(
-                \\size {d}
-                \\names {d}
-            , .{ size, entries });
-            try writer.writeByte('\n');
-            var i: u32 = 0;
-            while (i < entries) : (i += 1) {
-                const index = try std.leb.readULEB128(u32, reader);
-                const name_len = try std.leb.readULEB128(u32, reader);
-                const pos = reader.context.pos;
-                const name = data[pos..][0..name_len];
-                reader.context.pos += name_len;
+            switch (try parseDumpType(step, std.wasm.NameSubsection, reader, writer)) {
+                // The module name subsection ... consists of a single name
+                // that is assigned to the module itself.
+                .module => {
+                    const size = try std.leb.readULEB128(u32, reader);
+                    const name_len = try std.leb.readULEB128(u32, reader);
+                    if (size != name_len + 1) return error.BadSubsectionSize;
+                    if (reader.context.pos + name_len > data.len) return error.UnexpectedEndOfStream;
+                    try writer.print("name {s}\n", .{data[reader.context.pos..][0..name_len]});
+                    reader.context.pos += name_len;
+                },
 
-                try writer.print(
-                    \\index {d}
-                    \\name {s}
-                , .{ index, name });
-                try writer.writeByte('\n');
+                // The function name subsection ... consists of a name map
+                // assigning function names to function indices.
+                .function, .global, .data_segment => {
+                    const size = try std.leb.readULEB128(u32, reader);
+                    const entries = try std.leb.readULEB128(u32, reader);
+                    try writer.print(
+                        \\size {d}
+                        \\names {d}
+                        \\
+                    , .{ size, entries });
+                    for (0..entries) |_| {
+                        const index = try std.leb.readULEB128(u32, reader);
+                        const name_len = try std.leb.readULEB128(u32, reader);
+                        if (reader.context.pos + name_len > data.len) return error.UnexpectedEndOfStream;
+                        const name = data[reader.context.pos..][0..name_len];
+                        reader.context.pos += name.len;
+
+                        try writer.print(
+                            \\index {d}
+                            \\name {s}
+                            \\
+                        , .{ index, name });
+                    }
+                },
+
+                // The local name subsection ... consists of an indirect name
+                // map assigning local names to local indices grouped by
+                // function indices.
+                .local => {
+                    return step.fail("TODO implement parseDumpNames for local subsections", .{});
+                },
+
+                else => |t| return step.fail("invalid subsection type: {s}", .{@tagName(t)}),
             }
         }
     }
diff --git a/lib/std/Build/Step/Compile.zig b/lib/std/Build/Step/Compile.zig
index 9e94b78d6c..5bf0805e79 100644
--- a/lib/std/Build/Step/Compile.zig
+++ b/lib/std/Build/Step/Compile.zig
@@ -591,7 +591,7 @@ pub fn dependsOnSystemLibrary(self: *const Compile, name: []const u8) bool {
                 else => continue,
             }
         }
-        is_linking_libc = is_linking_libc or module.link_libcpp == true;
+        is_linking_libc = is_linking_libc or module.link_libc == true;
         is_linking_libcpp = is_linking_libcpp or module.link_libcpp == true;
     }
 
@@ -1277,7 +1277,7 @@ fn make(step: *Step, prog_node: *std.Progress.Node) !void {
                     .win32_resource_file => |rc_source_file| l: {
                         if (!my_responsibility) break :l;
 
-                        if (rc_source_file.flags.len == 0) {
+                        if (rc_source_file.flags.len == 0 and rc_source_file.include_paths.len == 0) {
                             if (prev_has_rcflags) {
                                 try zig_args.append("-rcflags");
                                 try zig_args.append("--");
@@ -1288,6 +1288,10 @@ fn make(step: *Step, prog_node: *std.Progress.Node) !void {
                             for (rc_source_file.flags) |arg| {
                                 try zig_args.append(arg);
                             }
+                            for (rc_source_file.include_paths) |include_path| {
+                                try zig_args.append("/I");
+                                try zig_args.append(include_path.getPath2(module.owner, step));
+                            }
                             try zig_args.append("--");
                             prev_has_rcflags = true;
                         }
diff --git a/lib/std/Thread.zig b/lib/std/Thread.zig
index d1c8a24f0a..503f646dc4 100644
--- a/lib/std/Thread.zig
+++ b/lib/std/Thread.zig
@@ -844,19 +844,19 @@ const WasiThreadImpl = struct {
                 const bad_fn_ret = "expected return type of startFn to be 'u8', 'noreturn', 'void', or '!void'";
                 switch (@typeInfo(@typeInfo(@TypeOf(f)).Fn.return_type.?)) {
                     .NoReturn, .Void => {
-                        @call(.auto, w, args);
+                        @call(.auto, f, w.args);
                     },
                     .Int => |info| {
                         if (info.bits != 8) {
                             @compileError(bad_fn_ret);
                         }
-                        _ = @call(.auto, w, args); // WASI threads don't support exit status, ignore value
+                        _ = @call(.auto, f, w.args); // WASI threads don't support exit status, ignore value
                     },
                     .ErrorUnion => |info| {
                         if (info.payload != void) {
                             @compileError(bad_fn_ret);
                         }
-                        @call(.auto, f, args) catch |err| {
+                        @call(.auto, f, w.args) catch |err| {
                             std.debug.print("error: {s}\n", .{@errorName(err)});
                             if (@errorReturnTrace()) |trace| {
                                 std.debug.dumpStackTrace(trace.*);
diff --git a/lib/std/Thread/RwLock.zig b/lib/std/Thread/RwLock.zig
index c4a8755907..0e8da6239f 100644
--- a/lib/std/Thread/RwLock.zig
+++ b/lib/std/Thread/RwLock.zig
@@ -41,7 +41,9 @@ pub fn tryLockShared(rwl: *RwLock) bool {
     return rwl.impl.tryLockShared();
 }
 
-/// Blocks until shared lock ownership is acquired.
+/// Obtains shared lock ownership.
+/// Blocks if another thread has exclusive ownership.
+/// May block if another thread is attempting to get exclusive ownership.
 pub fn lockShared(rwl: *RwLock) void {
     return rwl.impl.lockShared();
 }
diff --git a/lib/std/child_process.zig b/lib/std/child_process.zig
index dcc00b77d5..05a4762fb9 100644
--- a/lib/std/child_process.zig
+++ b/lib/std/child_process.zig
@@ -31,10 +31,23 @@ pub const ChildProcess = struct {
 
     allocator: mem.Allocator,
 
+    /// The writing end of the child process's standard input pipe.
+    /// Usage requires `stdin_behavior == StdIo.Pipe`.
+    /// Available after calling `spawn()`.
     stdin: ?File,
+
+    /// The reading end of the child process's standard output pipe.
+    /// Usage requires `stdout_behavior == StdIo.Pipe`.
+    /// Available after calling `spawn()`.
     stdout: ?File,
+
+    /// The reading end of the child process's standard error pipe.
+    /// Usage requires `stderr_behavior == StdIo.Pipe`.
+    /// Available after calling `spawn()`.
     stderr: ?File,
 
+    /// Terminated state of the child process.
+    /// Available after calling `wait()`.
     term: ?(SpawnError!Term),
 
     argv: []const []const u8,
@@ -136,6 +149,14 @@ pub const ChildProcess = struct {
 
         /// Windows-only. `cwd` was provided, but the path did not exist when spawning the child process.
         CurrentWorkingDirectoryUnlinked,
+
+        /// Windows-only. NUL (U+0000), LF (U+000A), CR (U+000D) are not allowed
+        /// within arguments when executing a `.bat`/`.cmd` script.
+        /// - NUL/LF signifiies end of arguments, so anything afterwards
+        ///   would be lost after execution.
+        /// - CR is stripped by `cmd.exe`, so any CR codepoints
+        ///   would be lost after execution.
+        InvalidBatchScriptArg,
     } ||
         posix.ExecveError ||
         posix.SetIdError ||
@@ -151,10 +172,23 @@ pub const ChildProcess = struct {
         Unknown: u32,
     };
 
+    /// Behavior of the child process's standard input, output, and error
+    /// streams.
     pub const StdIo = enum {
+        /// Inherit the stream from the parent process.
         Inherit,
+
+        /// Pass a null stream to the child process.
+        /// This is /dev/null on POSIX and NUL on Windows.
         Ignore,
+
+        /// Create a pipe for the stream.
+        /// The corresponding field (`stdout`, `stderr`, or `stdin`)
+        /// will be assigned a `File` object that can be used
+        /// to read from or write to the pipe.
         Pipe,
+
+        /// Close the stream after the child process spawns.
         Close,
     };
 
@@ -495,7 +529,18 @@ pub const ChildProcess = struct {
     }
 
     fn spawnPosix(self: *ChildProcess) SpawnError!void {
-        const pipe_flags: posix.O = .{};
+        // The child process does need to access (one end of) these pipes. However,
+        // we must initially set CLOEXEC to avoid a race condition. If another thread
+        // is racing to spawn a different child process, we don't want it to inherit
+        // these FDs in any scenario; that would mean that, for instance, calls to
+        // `poll` from the parent would not report the child's stdout as closing when
+        // expected, since the other child may retain a reference to the write end of
+        // the pipe. So, we create the pipes with CLOEXEC initially. After fork, we
+        // need to do something in the new child to make sure we preserve the reference
+        // we want. We could use `fcntl` to remove CLOEXEC from the FD, but as it
+        // turns out, we `dup2` everything anyway, so there's no need!
+        const pipe_flags: posix.O = .{ .CLOEXEC = true };
+
         const stdin_pipe = if (self.stdin_behavior == StdIo.Pipe) try posix.pipe2(pipe_flags) else undefined;
         errdefer if (self.stdin_behavior == StdIo.Pipe) {
             destroyPipe(stdin_pipe);
@@ -583,19 +628,6 @@ pub const ChildProcess = struct {
             setUpChildIo(self.stdout_behavior, stdout_pipe[1], posix.STDOUT_FILENO, dev_null_fd) catch |err| forkChildErrReport(err_pipe[1], err);
             setUpChildIo(self.stderr_behavior, stderr_pipe[1], posix.STDERR_FILENO, dev_null_fd) catch |err| forkChildErrReport(err_pipe[1], err);
 
-            if (self.stdin_behavior == .Pipe) {
-                posix.close(stdin_pipe[0]);
-                posix.close(stdin_pipe[1]);
-            }
-            if (self.stdout_behavior == .Pipe) {
-                posix.close(stdout_pipe[0]);
-                posix.close(stdout_pipe[1]);
-            }
-            if (self.stderr_behavior == .Pipe) {
-                posix.close(stderr_pipe[0]);
-                posix.close(stderr_pipe[1]);
-            }
-
             if (self.cwd_dir) |cwd| {
                 posix.fchdir(cwd.fd) catch |err| forkChildErrReport(err_pipe[1], err);
             } else if (self.cwd) |cwd| {
@@ -814,17 +846,20 @@ pub const ChildProcess = struct {
         const app_name_w = try unicode.wtf8ToWtf16LeAllocZ(self.allocator, app_basename_wtf8);
         defer self.allocator.free(app_name_w);
 
-        const cmd_line_w = argvToCommandLineWindows(self.allocator, self.argv) catch |err| switch (err) {
-            // argv[0] contains unsupported characters that will never resolve to a valid exe.
-            error.InvalidArg0 => return error.FileNotFound,
-            else => |e| return e,
-        };
-        defer self.allocator.free(cmd_line_w);
-
         run: {
             const PATH: [:0]const u16 = std.process.getenvW(unicode.utf8ToUtf16LeStringLiteral("PATH")) orelse &[_:0]u16{};
             const PATHEXT: [:0]const u16 = std.process.getenvW(unicode.utf8ToUtf16LeStringLiteral("PATHEXT")) orelse &[_:0]u16{};
 
+            // In case the command ends up being a .bat/.cmd script, we need to escape things using the cmd.exe rules
+            // and invoke cmd.exe ourselves in order to mitigate arbitrary command execution from maliciously
+            // constructed arguments.
+            //
+            // We'll need to wait until we're actually trying to run the command to know for sure
+            // if the resolved command has the `.bat` or `.cmd` extension, so we defer actually
+            // serializing the command line until we determine how it should be serialized.
+            var cmd_line_cache = WindowsCommandLineCache.init(self.allocator, self.argv);
+            defer cmd_line_cache.deinit();
+
             var app_buf = std.ArrayListUnmanaged(u16){};
             defer app_buf.deinit(self.allocator);
 
@@ -846,8 +881,10 @@ pub const ChildProcess = struct {
                 dir_buf.shrinkRetainingCapacity(normalized_len);
             }
 
-            windowsCreateProcessPathExt(self.allocator, &dir_buf, &app_buf, PATHEXT, cmd_line_w.ptr, envp_ptr, cwd_w_ptr, &siStartInfo, &piProcInfo) catch |no_path_err| {
+            windowsCreateProcessPathExt(self.allocator, &dir_buf, &app_buf, PATHEXT, &cmd_line_cache, envp_ptr, cwd_w_ptr, &siStartInfo, &piProcInfo) catch |no_path_err| {
                 const original_err = switch (no_path_err) {
+                    // argv[0] contains unsupported characters that will never resolve to a valid exe.
+                    error.InvalidArg0 => return error.FileNotFound,
                     error.FileNotFound, error.InvalidExe, error.AccessDenied => |e| e,
                     error.UnrecoverableInvalidExe => return error.InvalidExe,
                     else => |e| return e,
@@ -872,9 +909,11 @@ pub const ChildProcess = struct {
                     const normalized_len = windows.normalizePath(u16, dir_buf.items) catch continue;
                     dir_buf.shrinkRetainingCapacity(normalized_len);
 
-                    if (windowsCreateProcessPathExt(self.allocator, &dir_buf, &app_buf, PATHEXT, cmd_line_w.ptr, envp_ptr, cwd_w_ptr, &siStartInfo, &piProcInfo)) {
+                    if (windowsCreateProcessPathExt(self.allocator, &dir_buf, &app_buf, PATHEXT, &cmd_line_cache, envp_ptr, cwd_w_ptr, &siStartInfo, &piProcInfo)) {
                         break :run;
                     } else |err| switch (err) {
+                        // argv[0] contains unsupported characters that will never resolve to a valid exe.
+                        error.InvalidArg0 => return error.FileNotFound,
                         error.FileNotFound, error.AccessDenied, error.InvalidExe => continue,
                         error.UnrecoverableInvalidExe => return error.InvalidExe,
                         else => |e| return e,
@@ -935,7 +974,7 @@ fn windowsCreateProcessPathExt(
     dir_buf: *std.ArrayListUnmanaged(u16),
     app_buf: *std.ArrayListUnmanaged(u16),
     pathext: [:0]const u16,
-    cmd_line: [*:0]u16,
+    cmd_line_cache: *WindowsCommandLineCache,
     envp_ptr: ?[*]u16,
     cwd_ptr: ?[*:0]u16,
     lpStartupInfo: *windows.STARTUPINFOW,
@@ -1069,7 +1108,26 @@ fn windowsCreateProcessPathExt(
             try dir_buf.append(allocator, 0);
             const full_app_name = dir_buf.items[0 .. dir_buf.items.len - 1 :0];
 
-            if (windowsCreateProcess(full_app_name.ptr, cmd_line, envp_ptr, cwd_ptr, lpStartupInfo, lpProcessInformation)) |_| {
+            const is_bat_or_cmd = bat_or_cmd: {
+                const app_name = app_buf.items[0..app_name_len];
+                const ext_start = std.mem.lastIndexOfScalar(u16, app_name, '.') orelse break :bat_or_cmd false;
+                const ext = app_name[ext_start..];
+                const ext_enum = windowsCreateProcessSupportsExtension(ext) orelse break :bat_or_cmd false;
+                switch (ext_enum) {
+                    .cmd, .bat => break :bat_or_cmd true,
+                    else => break :bat_or_cmd false,
+                }
+            };
+            const cmd_line_w = if (is_bat_or_cmd)
+                try cmd_line_cache.scriptCommandLine(full_app_name)
+            else
+                try cmd_line_cache.commandLine();
+            const app_name_w = if (is_bat_or_cmd)
+                try cmd_line_cache.cmdExePath()
+            else
+                full_app_name;
+
+            if (windowsCreateProcess(app_name_w.ptr, cmd_line_w.ptr, envp_ptr, cwd_ptr, lpStartupInfo, lpProcessInformation)) |_| {
                 return;
             } else |err| switch (err) {
                 error.FileNotFound,
@@ -1111,7 +1169,20 @@ fn windowsCreateProcessPathExt(
         try dir_buf.append(allocator, 0);
         const full_app_name = dir_buf.items[0 .. dir_buf.items.len - 1 :0];
 
-        if (windowsCreateProcess(full_app_name.ptr, cmd_line, envp_ptr, cwd_ptr, lpStartupInfo, lpProcessInformation)) |_| {
+        const is_bat_or_cmd = switch (ext_enum) {
+            .cmd, .bat => true,
+            else => false,
+        };
+        const cmd_line_w = if (is_bat_or_cmd)
+            try cmd_line_cache.scriptCommandLine(full_app_name)
+        else
+            try cmd_line_cache.commandLine();
+        const app_name_w = if (is_bat_or_cmd)
+            try cmd_line_cache.cmdExePath()
+        else
+            full_app_name;
+
+        if (windowsCreateProcess(app_name_w.ptr, cmd_line_w.ptr, envp_ptr, cwd_ptr, lpStartupInfo, lpProcessInformation)) |_| {
             return;
         } else |err| switch (err) {
             error.FileNotFound => continue,
@@ -1236,6 +1307,223 @@ test windowsCreateProcessSupportsExtension {
     try std.testing.expect(windowsCreateProcessSupportsExtension(&[_]u16{ '.', 'e', 'X', 'e', 'c' }) == null);
 }
 
+/// Serializes argv into a WTF-16 encoded command-line string for use with CreateProcessW.
+///
+/// Serialization is done on-demand and the result is cached in order to allow for:
+/// - Only serializing the particular type of command line needed (`.bat`/`.cmd`
+///   command line serialization is different from `.exe`/etc)
+/// - Reusing the serialized command lines if necessary (i.e. if the execution
+///   of a command fails and the PATH is going to be continued to be searched
+///   for more candidates)
+pub const WindowsCommandLineCache = struct {
+    cmd_line: ?[:0]u16 = null,
+    script_cmd_line: ?[:0]u16 = null,
+    cmd_exe_path: ?[:0]u16 = null,
+    argv: []const []const u8,
+    allocator: mem.Allocator,
+
+    pub fn init(allocator: mem.Allocator, argv: []const []const u8) WindowsCommandLineCache {
+        return .{
+            .allocator = allocator,
+            .argv = argv,
+        };
+    }
+
+    pub fn deinit(self: *WindowsCommandLineCache) void {
+        if (self.cmd_line) |cmd_line| self.allocator.free(cmd_line);
+        if (self.script_cmd_line) |script_cmd_line| self.allocator.free(script_cmd_line);
+        if (self.cmd_exe_path) |cmd_exe_path| self.allocator.free(cmd_exe_path);
+    }
+
+    pub fn commandLine(self: *WindowsCommandLineCache) ![:0]u16 {
+        if (self.cmd_line == null) {
+            self.cmd_line = try argvToCommandLineWindows(self.allocator, self.argv);
+        }
+        return self.cmd_line.?;
+    }
+
+    /// Not cached, since the path to the batch script will change during PATH searching.
+    /// `script_path` should be as qualified as possible, e.g. if the PATH is being searched,
+    /// then script_path should include both the search path and the script filename
+    /// (this allows avoiding cmd.exe having to search the PATH again).
+    pub fn scriptCommandLine(self: *WindowsCommandLineCache, script_path: []const u16) ![:0]u16 {
+        if (self.script_cmd_line) |v| self.allocator.free(v);
+        self.script_cmd_line = try argvToScriptCommandLineWindows(
+            self.allocator,
+            script_path,
+            self.argv[1..],
+        );
+        return self.script_cmd_line.?;
+    }
+
+    pub fn cmdExePath(self: *WindowsCommandLineCache) ![:0]u16 {
+        if (self.cmd_exe_path == null) {
+            self.cmd_exe_path = try windowsCmdExePath(self.allocator);
+        }
+        return self.cmd_exe_path.?;
+    }
+};
+
+pub fn windowsCmdExePath(allocator: mem.Allocator) error{ OutOfMemory, Unexpected }![:0]u16 {
+    var buf = try std.ArrayListUnmanaged(u16).initCapacity(allocator, 128);
+    errdefer buf.deinit(allocator);
+    while (true) {
+        const unused_slice = buf.unusedCapacitySlice();
+        // TODO: Get the system directory from PEB.ReadOnlyStaticServerData
+        const len = windows.kernel32.GetSystemDirectoryW(@ptrCast(unused_slice), @intCast(unused_slice.len));
+        if (len == 0) {
+            switch (windows.kernel32.GetLastError()) {
+                else => |err| return windows.unexpectedError(err),
+            }
+        }
+        if (len > unused_slice.len) {
+            try buf.ensureUnusedCapacity(allocator, len);
+        } else {
+            buf.items.len = len;
+            break;
+        }
+    }
+    switch (buf.items[buf.items.len - 1]) {
+        '/', '\\' => {},
+        else => try buf.append(allocator, fs.path.sep),
+    }
+    try buf.appendSlice(allocator, std.unicode.utf8ToUtf16LeStringLiteral("cmd.exe"));
+    return try buf.toOwnedSliceSentinel(allocator, 0);
+}
+
+pub const ArgvToScriptCommandLineError = error{
+    OutOfMemory,
+    InvalidWtf8,
+    /// NUL (U+0000), LF (U+000A), CR (U+000D) are not allowed
+    /// within arguments when executing a `.bat`/`.cmd` script.
+    /// - NUL/LF signifiies end of arguments, so anything afterwards
+    ///   would be lost after execution.
+    /// - CR is stripped by `cmd.exe`, so any CR codepoints
+    ///   would be lost after execution.
+    InvalidBatchScriptArg,
+};
+
+/// Serializes `argv` to a Windows command-line string that uses `cmd.exe /c` and `cmd.exe`-specific
+/// escaping rules. The caller owns the returned slice.
+///
+/// Escapes `argv` using the suggested mitigation against arbitrary command execution from:
+/// https://flatt.tech/research/posts/batbadbut-you-cant-securely-execute-commands-on-windows/
+pub fn argvToScriptCommandLineWindows(
+    allocator: mem.Allocator,
+    /// Path to the `.bat`/`.cmd` script. If this path is relative, it is assumed to be relative to the CWD.
+    /// The script must have been verified to exist at this path before calling this function.
+    script_path: []const u16,
+    /// Arguments, not including the script name itself. Expected to be encoded as WTF-8.
+    script_args: []const []const u8,
+) ArgvToScriptCommandLineError![:0]u16 {
+    var buf = try std.ArrayList(u8).initCapacity(allocator, 64);
+    defer buf.deinit();
+
+    // `/d` disables execution of AutoRun commands.
+    // `/e:ON` and `/v:OFF` are needed for BatBadBut mitigation:
+    // > If delayed expansion is enabled via the registry value DelayedExpansion,
+    // > it must be disabled by explicitly calling cmd.exe with the /V:OFF option.
+    // > Escaping for % requires the command extension to be enabled.
+    // > If it’s disabled via the registry value EnableExtensions, it must be enabled with the /E:ON option.
+    // https://flatt.tech/research/posts/batbadbut-you-cant-securely-execute-commands-on-windows/
+    buf.appendSliceAssumeCapacity("cmd.exe /d /e:ON /v:OFF /c \"");
+
+    // Always quote the path to the script arg
+    buf.appendAssumeCapacity('"');
+    // We always want the path to the batch script to include a path separator in order to
+    // avoid cmd.exe searching the PATH for the script. This is not part of the arbitrary
+    // command execution mitigation, we just know exactly what script we want to execute
+    // at this point, and potentially making cmd.exe re-find it is unnecessary.
+    //
+    // If the script path does not have a path separator, then we know its relative to CWD and
+    // we can just put `.\` in the front.
+    if (mem.indexOfAny(u16, script_path, &[_]u16{ mem.nativeToLittle(u16, '\\'), mem.nativeToLittle(u16, '/') }) == null) {
+        try buf.appendSlice(".\\");
+    }
+    // Note that we don't do any escaping/mitigations for this argument, since the relevant
+    // characters (", %, etc) are illegal in file paths and this function should only be called
+    // with script paths that have been verified to exist.
+    try std.unicode.wtf16LeToWtf8ArrayList(&buf, script_path);
+    buf.appendAssumeCapacity('"');
+
+    for (script_args) |arg| {
+        // Literal carriage returns get stripped when run through cmd.exe
+        // and NUL/newlines act as 'end of command.' Because of this, it's basically
+        // always a mistake to include these characters in argv, so it's
+        // an error condition in order to ensure that the return of this
+        // function can always roundtrip through cmd.exe.
+        if (std.mem.indexOfAny(u8, arg, "\x00\r\n") != null) {
+            return error.InvalidBatchScriptArg;
+        }
+
+        // Separate args with a space.
+        try buf.append(' ');
+
+        // Need to quote if the argument is empty (otherwise the arg would just be lost)
+        // or if the last character is a `\`, since then something like "%~2" in a .bat
+        // script would cause the closing " to be escaped which we don't want.
+        var needs_quotes = arg.len == 0 or arg[arg.len - 1] == '\\';
+        if (!needs_quotes) {
+            for (arg) |c| {
+                switch (c) {
+                    // Known good characters that don't need to be quoted
+                    'A'...'Z', 'a'...'z', '0'...'9', '#', '$', '*', '+', '-', '.', '/', ':', '?', '@', '\\', '_' => {},
+                    // When in doubt, quote
+                    else => {
+                        needs_quotes = true;
+                        break;
+                    },
+                }
+            }
+        }
+        if (needs_quotes) {
+            try buf.append('"');
+        }
+        var backslashes: usize = 0;
+        for (arg) |c| {
+            switch (c) {
+                '\\' => {
+                    backslashes += 1;
+                },
+                '"' => {
+                    try buf.appendNTimes('\\', backslashes);
+                    try buf.append('"');
+                    backslashes = 0;
+                },
+                // Replace `%` with `%%cd:~,%`.
+                //
+                // cmd.exe allows extracting a substring from an environment
+                // variable with the syntax: `%foo:~<start_index>,<end_index>%`.
+                // Therefore, `%cd:~,%` will always expand to an empty string
+                // since both the start and end index are blank, and it is assumed
+                // that `%cd%` is always available since it is a built-in variable
+                // that corresponds to the current directory.
+                //
+                // This means that replacing `%foo%` with `%%cd:~,%foo%%cd:~,%`
+                // will stop `%foo%` from being expanded and *after* expansion
+                // we'll still be left with `%foo%` (the literal string).
+                '%' => {
+                    // the trailing `%` is appended outside the switch
+                    try buf.appendSlice("%%cd:~,");
+                    backslashes = 0;
+                },
+                else => {
+                    backslashes = 0;
+                },
+            }
+            try buf.append(c);
+        }
+        if (needs_quotes) {
+            try buf.appendNTimes('\\', backslashes);
+            try buf.append('"');
+        }
+    }
+
+    try buf.append('"');
+
+    return try unicode.wtf8ToWtf16LeAllocZ(allocator, buf.items);
+}
+
 pub const ArgvToCommandLineError = error{ OutOfMemory, InvalidWtf8, InvalidArg0 };
 
 /// Serializes `argv` to a Windows command-line string suitable for passing to a child process and
diff --git a/lib/std/compress/flate/inflate.zig b/lib/std/compress/flate/inflate.zig
index cf23961b21..69ee41e096 100644
--- a/lib/std/compress/flate/inflate.zig
+++ b/lib/std/compress/flate/inflate.zig
@@ -347,6 +347,7 @@ pub fn Inflate(comptime container: Container, comptime LookaheadType: type, comp
         /// If the number of bytes read is 0, it means end of stream.
         /// End of stream is not an error condition.
         pub fn read(self: *Self, buffer: []u8) Error!usize {
+            if (buffer.len == 0) return 0;
             const out = try self.get(buffer.len);
             @memcpy(buffer[0..out.len], out);
             return out.len;
@@ -556,3 +557,14 @@ test "bug 18966" {
     try decompress(.gzip, in.reader(), out.writer());
     try testing.expectEqualStrings(expect, out.items);
 }
+
+test "bug 19895" {
+    const input = &[_]u8{
+        0b0000_0001, 0b0000_1100, 0x00, 0b1111_0011, 0xff, // deflate fixed buffer header len, nlen
+        'H', 'e', 'l', 'l', 'o', ' ', 'w', 'o', 'r', 'l', 'd', 0x0a, // non compressed data
+    };
+    var in = std.io.fixedBufferStream(input);
+    var decomp = decompressor(.raw, in.reader());
+    var buf: [0]u8 = undefined;
+    try testing.expectEqual(0, try decomp.read(&buf));
+}
diff --git a/lib/std/crypto/ff.zig b/lib/std/crypto/ff.zig
index b917ce7a43..31792318d0 100644
--- a/lib/std/crypto/ff.zig
+++ b/lib/std/crypto/ff.zig
@@ -843,7 +843,7 @@ const ct_protected = struct {
 
     // Compares two big integers in constant time, returning true if x >= y.
     fn limbsCmpGeq(x: anytype, y: @TypeOf(x)) bool {
-        return !ct.limbsCmpLt(x, y);
+        return !limbsCmpLt(x, y);
     }
 
     // Multiplies two limbs and returns the result as a wide limb.
@@ -878,11 +878,11 @@ const ct_unprotected = struct {
 
     // Compares two big integers in constant time, returning true if x < y.
     fn limbsCmpLt(x: anytype, y: @TypeOf(x)) bool {
-        assert(x.limbs_count() == y.limbs_count());
-        const x_limbs = x.limbs.constSlice();
-        const y_limbs = y.limbs.constSlice();
+        const x_limbs = x.limbsConst();
+        const y_limbs = y.limbsConst();
+        assert(x_limbs.len == y_limbs.len);
 
-        var i = x.limbs_count();
+        var i = x_limbs.len;
         while (i != 0) {
             i -= 1;
             if (x_limbs[i] != y_limbs[i]) {
@@ -894,7 +894,7 @@ const ct_unprotected = struct {
 
     // Compares two big integers in constant time, returning true if x >= y.
     fn limbsCmpGeq(x: anytype, y: @TypeOf(x)) bool {
-        return !ct.limbsCmpLt(x, y);
+        return !limbsCmpLt(x, y);
     }
 
     // Multiplies two limbs and returns the result as a wide limb.
@@ -961,3 +961,28 @@ test "finite field arithmetic" {
     try testing.expect(x_sq3.eql(x_sq4));
     try m.fromMontgomery(&x);
 }
+
+fn testCt(ct_: anytype) !void {
+    if (builtin.zig_backend == .stage2_c) return error.SkipZigTest;
+
+    const l0: Limb = 0;
+    const l1: Limb = 1;
+    try testing.expectEqual(l1, ct_.select(true, l1, l0));
+    try testing.expectEqual(l0, ct_.select(false, l1, l0));
+    try testing.expectEqual(false, ct_.eql(l1, l0));
+    try testing.expectEqual(true, ct_.eql(l1, l1));
+
+    const M = Modulus(256);
+    const m = try M.fromPrimitive(u256, 3429938563481314093726330772853735541133072814650493833233);
+    const x = try M.Fe.fromPrimitive(u256, m, 80169837251094269539116136208111827396136208141182357733);
+    const y = try M.Fe.fromPrimitive(u256, m, 24620149608466364616251608466389896540098571);
+    try testing.expectEqual(false, ct_.limbsCmpLt(x.v, y.v));
+    try testing.expectEqual(true, ct_.limbsCmpGeq(x.v, y.v));
+
+    try testing.expectEqual(WideLimb{ .hi = 0, .lo = 0x88 }, ct_.mulWide(1 << 3, (1 << 4) + 1));
+}
+
+test ct {
+    try testCt(ct_protected);
+    try testCt(ct_unprotected);
+}
diff --git a/lib/std/debug.zig b/lib/std/debug.zig
index eaa5ca9ff7..c7d4818e18 100644
--- a/lib/std/debug.zig
+++ b/lib/std/debug.zig
@@ -228,8 +228,8 @@ pub fn relocateContext(context: *ThreadContext) void {
     };
 }
 
-pub const have_getcontext = @hasDecl(posix.system, "getcontext") and
-    native_os != .openbsd and native_os != .haiku and
+pub const have_getcontext = native_os != .openbsd and native_os != .haiku and
+    !builtin.target.isAndroid() and
     (native_os != .linux or switch (builtin.cpu.arch) {
     .x86,
     .x86_64,
diff --git a/lib/std/enums.zig b/lib/std/enums.zig
index c00bf52aa6..aea194683d 100644
--- a/lib/std/enums.zig
+++ b/lib/std/enums.zig
@@ -452,7 +452,7 @@ pub fn EnumMap(comptime E: type, comptime V: type) type {
         values: [Indexer.count]Value = undefined,
 
         /// Initializes the map using a sparse struct of optionals
-        pub fn init(init_values: EnumFieldStruct(E, ?Value, null)) Self {
+        pub fn init(init_values: EnumFieldStruct(E, ?Value, @as(?Value, null))) Self {
             @setEvalBranchQuota(2 * @typeInfo(E).Enum.fields.len);
             var result: Self = .{};
             if (@typeInfo(E).Enum.is_exhaustive) {
@@ -652,6 +652,19 @@ pub fn EnumMap(comptime E: type, comptime V: type) type {
     };
 }
 
+test EnumMap {
+    const Ball = enum { red, green, blue };
+
+    const some = EnumMap(Ball, u8).init(.{
+        .green = 0xff,
+        .blue = 0x80,
+    });
+    try testing.expectEqual(2, some.count());
+    try testing.expectEqual(null, some.get(.red));
+    try testing.expectEqual(0xff, some.get(.green));
+    try testing.expectEqual(0x80, some.get(.blue));
+}
+
 /// A multiset of enum elements up to a count of usize. Backed
 /// by an EnumArray. This type does no dynamic allocation and can
 /// be copied by value.
diff --git a/lib/std/fmt.zig b/lib/std/fmt.zig
index 37c9f77fec..8965d1bc0e 100644
--- a/lib/std/fmt.zig
+++ b/lib/std/fmt.zig
@@ -1501,9 +1501,9 @@ pub fn parseInt(comptime T: type, buf: []const u8, base: u8) ParseIntError!T {
 }
 
 test parseInt {
-    try std.testing.expect((try parseInt(i32, "-10", 10)) == -10);
-    try std.testing.expect((try parseInt(i32, "+10", 10)) == 10);
-    try std.testing.expect((try parseInt(u32, "+10", 10)) == 10);
+    try std.testing.expectEqual(-10, try parseInt(i32, "-10", 10));
+    try std.testing.expectEqual(10, try parseInt(i32, "+10", 10));
+    try std.testing.expectEqual(10, try parseInt(u32, "+10", 10));
     try std.testing.expectError(error.Overflow, parseInt(u32, "-10", 10));
     try std.testing.expectError(error.InvalidCharacter, parseInt(u32, " 10", 10));
     try std.testing.expectError(error.InvalidCharacter, parseInt(u32, "10 ", 10));
@@ -1511,17 +1511,17 @@ test parseInt {
     try std.testing.expectError(error.InvalidCharacter, parseInt(u32, "0x_10_", 10));
     try std.testing.expectError(error.InvalidCharacter, parseInt(u32, "0x10_", 10));
     try std.testing.expectError(error.InvalidCharacter, parseInt(u32, "0x_10", 10));
-    try std.testing.expect((try parseInt(u8, "255", 10)) == 255);
+    try std.testing.expectEqual(255, try parseInt(u8, "255", 10));
     try std.testing.expectError(error.Overflow, parseInt(u8, "256", 10));
 
     // +0 and -0 should work for unsigned
-    try std.testing.expect((try parseInt(u8, "-0", 10)) == 0);
-    try std.testing.expect((try parseInt(u8, "+0", 10)) == 0);
+    try std.testing.expectEqual(0, try parseInt(u8, "-0", 10));
+    try std.testing.expectEqual(0, try parseInt(u8, "+0", 10));
 
     // ensure minInt is parsed correctly
-    try std.testing.expect((try parseInt(i1, "-1", 10)) == math.minInt(i1));
-    try std.testing.expect((try parseInt(i8, "-128", 10)) == math.minInt(i8));
-    try std.testing.expect((try parseInt(i43, "-4398046511104", 10)) == math.minInt(i43));
+    try std.testing.expectEqual(math.minInt(i1), try parseInt(i1, "-1", 10));
+    try std.testing.expectEqual(math.minInt(i8), try parseInt(i8, "-128", 10));
+    try std.testing.expectEqual(math.minInt(i43), try parseInt(i43, "-4398046511104", 10));
 
     // empty string or bare +- is invalid
     try std.testing.expectError(error.InvalidCharacter, parseInt(u32, "", 10));
@@ -1532,22 +1532,22 @@ test parseInt {
     try std.testing.expectError(error.InvalidCharacter, parseInt(i32, "-", 10));
 
     // autodectect the base
-    try std.testing.expect((try parseInt(i32, "111", 0)) == 111);
-    try std.testing.expect((try parseInt(i32, "1_1_1", 0)) == 111);
-    try std.testing.expect((try parseInt(i32, "1_1_1", 0)) == 111);
-    try std.testing.expect((try parseInt(i32, "+0b111", 0)) == 7);
-    try std.testing.expect((try parseInt(i32, "+0B111", 0)) == 7);
-    try std.testing.expect((try parseInt(i32, "+0b1_11", 0)) == 7);
-    try std.testing.expect((try parseInt(i32, "+0o111", 0)) == 73);
-    try std.testing.expect((try parseInt(i32, "+0O111", 0)) == 73);
-    try std.testing.expect((try parseInt(i32, "+0o11_1", 0)) == 73);
-    try std.testing.expect((try parseInt(i32, "+0x111", 0)) == 273);
-    try std.testing.expect((try parseInt(i32, "-0b111", 0)) == -7);
-    try std.testing.expect((try parseInt(i32, "-0b11_1", 0)) == -7);
-    try std.testing.expect((try parseInt(i32, "-0o111", 0)) == -73);
-    try std.testing.expect((try parseInt(i32, "-0x111", 0)) == -273);
-    try std.testing.expect((try parseInt(i32, "-0X111", 0)) == -273);
-    try std.testing.expect((try parseInt(i32, "-0x1_11", 0)) == -273);
+    try std.testing.expectEqual(111, try parseInt(i32, "111", 0));
+    try std.testing.expectEqual(111, try parseInt(i32, "1_1_1", 0));
+    try std.testing.expectEqual(111, try parseInt(i32, "1_1_1", 0));
+    try std.testing.expectEqual(7, try parseInt(i32, "+0b111", 0));
+    try std.testing.expectEqual(7, try parseInt(i32, "+0B111", 0));
+    try std.testing.expectEqual(7, try parseInt(i32, "+0b1_11", 0));
+    try std.testing.expectEqual(73, try parseInt(i32, "+0o111", 0));
+    try std.testing.expectEqual(73, try parseInt(i32, "+0O111", 0));
+    try std.testing.expectEqual(73, try parseInt(i32, "+0o11_1", 0));
+    try std.testing.expectEqual(273, try parseInt(i32, "+0x111", 0));
+    try std.testing.expectEqual(-7, try parseInt(i32, "-0b111", 0));
+    try std.testing.expectEqual(-7, try parseInt(i32, "-0b11_1", 0));
+    try std.testing.expectEqual(-73, try parseInt(i32, "-0o111", 0));
+    try std.testing.expectEqual(-273, try parseInt(i32, "-0x111", 0));
+    try std.testing.expectEqual(-273, try parseInt(i32, "-0X111", 0));
+    try std.testing.expectEqual(-273, try parseInt(i32, "-0x1_11", 0));
 
     // bare binary/octal/decimal prefix is invalid
     try std.testing.expectError(error.InvalidCharacter, parseInt(u32, "0b", 0));
@@ -1643,31 +1643,31 @@ pub fn parseUnsigned(comptime T: type, buf: []const u8, base: u8) ParseIntError!
 }
 
 test parseUnsigned {
-    try std.testing.expect((try parseUnsigned(u16, "050124", 10)) == 50124);
-    try std.testing.expect((try parseUnsigned(u16, "65535", 10)) == 65535);
-    try std.testing.expect((try parseUnsigned(u16, "65_535", 10)) == 65535);
+    try std.testing.expectEqual(50124, try parseUnsigned(u16, "050124", 10));
+    try std.testing.expectEqual(65535, try parseUnsigned(u16, "65535", 10));
+    try std.testing.expectEqual(65535, try parseUnsigned(u16, "65_535", 10));
     try std.testing.expectError(error.Overflow, parseUnsigned(u16, "65536", 10));
 
-    try std.testing.expect((try parseUnsigned(u64, "0ffffffffffffffff", 16)) == 0xffffffffffffffff);
-    try std.testing.expect((try parseUnsigned(u64, "0f_fff_fff_fff_fff_fff", 16)) == 0xffffffffffffffff);
+    try std.testing.expectEqual(0xffffffffffffffff, try parseUnsigned(u64, "0ffffffffffffffff", 16));
+    try std.testing.expectEqual(0xffffffffffffffff, try parseUnsigned(u64, "0f_fff_fff_fff_fff_fff", 16));
     try std.testing.expectError(error.Overflow, parseUnsigned(u64, "10000000000000000", 16));
 
-    try std.testing.expect((try parseUnsigned(u32, "DeadBeef", 16)) == 0xDEADBEEF);
+    try std.testing.expectEqual(0xDEADBEEF, try parseUnsigned(u32, "DeadBeef", 16));
 
-    try std.testing.expect((try parseUnsigned(u7, "1", 10)) == 1);
-    try std.testing.expect((try parseUnsigned(u7, "1000", 2)) == 8);
+    try std.testing.expectEqual(1, try parseUnsigned(u7, "1", 10));
+    try std.testing.expectEqual(8, try parseUnsigned(u7, "1000", 2));
 
     try std.testing.expectError(error.InvalidCharacter, parseUnsigned(u32, "f", 10));
     try std.testing.expectError(error.InvalidCharacter, parseUnsigned(u8, "109", 8));
 
-    try std.testing.expect((try parseUnsigned(u32, "NUMBER", 36)) == 1442151747);
+    try std.testing.expectEqual(1442151747, try parseUnsigned(u32, "NUMBER", 36));
 
     // these numbers should fit even though the base itself doesn't fit in the destination type
-    try std.testing.expect((try parseUnsigned(u1, "0", 10)) == 0);
-    try std.testing.expect((try parseUnsigned(u1, "1", 10)) == 1);
+    try std.testing.expectEqual(0, try parseUnsigned(u1, "0", 10));
+    try std.testing.expectEqual(1, try parseUnsigned(u1, "1", 10));
     try std.testing.expectError(error.Overflow, parseUnsigned(u1, "2", 10));
-    try std.testing.expect((try parseUnsigned(u1, "001", 16)) == 1);
-    try std.testing.expect((try parseUnsigned(u2, "3", 16)) == 3);
+    try std.testing.expectEqual(1, try parseUnsigned(u1, "001", 16));
+    try std.testing.expectEqual(3, try parseUnsigned(u2, "3", 16));
     try std.testing.expectError(error.Overflow, parseUnsigned(u2, "4", 16));
 
     // parseUnsigned does not expect a sign
@@ -1717,15 +1717,15 @@ pub fn parseIntSizeSuffix(buf: []const u8, digit_base: u8) ParseIntError!usize {
 }
 
 test parseIntSizeSuffix {
-    try std.testing.expect(try parseIntSizeSuffix("2", 10) == 2);
-    try std.testing.expect(try parseIntSizeSuffix("2B", 10) == 2);
-    try std.testing.expect(try parseIntSizeSuffix("2kB", 10) == 2000);
-    try std.testing.expect(try parseIntSizeSuffix("2k", 10) == 2000);
-    try std.testing.expect(try parseIntSizeSuffix("2KiB", 10) == 2048);
-    try std.testing.expect(try parseIntSizeSuffix("2Ki", 10) == 2048);
-    try std.testing.expect(try parseIntSizeSuffix("aKiB", 16) == 10240);
-    try std.testing.expect(parseIntSizeSuffix("", 10) == error.InvalidCharacter);
-    try std.testing.expect(parseIntSizeSuffix("2iB", 10) == error.InvalidCharacter);
+    try std.testing.expectEqual(2, try parseIntSizeSuffix("2", 10));
+    try std.testing.expectEqual(2, try parseIntSizeSuffix("2B", 10));
+    try std.testing.expectEqual(2000, try parseIntSizeSuffix("2kB", 10));
+    try std.testing.expectEqual(2000, try parseIntSizeSuffix("2k", 10));
+    try std.testing.expectEqual(2048, try parseIntSizeSuffix("2KiB", 10));
+    try std.testing.expectEqual(2048, try parseIntSizeSuffix("2Ki", 10));
+    try std.testing.expectEqual(10240, try parseIntSizeSuffix("aKiB", 16));
+    try std.testing.expectError(error.InvalidCharacter, parseIntSizeSuffix("", 10));
+    try std.testing.expectError(error.InvalidCharacter, parseIntSizeSuffix("2iB", 10));
 }
 
 pub const parseFloat = @import("fmt/parse_float.zig").parseFloat;
@@ -1854,7 +1854,7 @@ test "parse u64 digit too big" {
 
 test "parse unsigned comptime" {
     comptime {
-        try std.testing.expect((try parseUnsigned(usize, "2", 10)) == 2);
+        try std.testing.expectEqual(2, try parseUnsigned(usize, "2", 10));
     }
 }
 
@@ -1963,15 +1963,15 @@ test "buffer" {
         var buf1: [32]u8 = undefined;
         var fbs = std.io.fixedBufferStream(&buf1);
         try formatType(1234, "", FormatOptions{}, fbs.writer(), std.options.fmt_max_depth);
-        try std.testing.expect(mem.eql(u8, fbs.getWritten(), "1234"));
+        try std.testing.expectEqualStrings("1234", fbs.getWritten());
 
         fbs.reset();
         try formatType('a', "c", FormatOptions{}, fbs.writer(), std.options.fmt_max_depth);
-        try std.testing.expect(mem.eql(u8, fbs.getWritten(), "a"));
+        try std.testing.expectEqualStrings("a", fbs.getWritten());
 
         fbs.reset();
         try formatType(0b1100, "b", FormatOptions{}, fbs.writer(), std.options.fmt_max_depth);
-        try std.testing.expect(mem.eql(u8, fbs.getWritten(), "1100"));
+        try std.testing.expectEqualStrings("1100", fbs.getWritten());
     }
 }
 
@@ -2372,10 +2372,10 @@ test "union" {
 
     var buf: [100]u8 = undefined;
     const uu_result = try bufPrint(buf[0..], "{}", .{uu_inst});
-    try std.testing.expect(mem.eql(u8, uu_result[0..18], "fmt.test.union.UU@"));
+    try std.testing.expectEqualStrings("fmt.test.union.UU@", uu_result[0..18]);
 
     const eu_result = try bufPrint(buf[0..], "{}", .{eu_inst});
-    try std.testing.expect(mem.eql(u8, eu_result[0..18], "fmt.test.union.EU@"));
+    try std.testing.expectEqualStrings("fmt.test.union.EU@", eu_result[0..18]);
 }
 
 test "struct.self-referential" {
@@ -2476,7 +2476,7 @@ test "formatIntValue with comptime_int" {
     var buf: [20]u8 = undefined;
     var fbs = std.io.fixedBufferStream(&buf);
     try formatIntValue(value, "", FormatOptions{}, fbs.writer());
-    try std.testing.expect(mem.eql(u8, fbs.getWritten(), "123456789123456789"));
+    try std.testing.expectEqualStrings("123456789123456789", fbs.getWritten());
 }
 
 test "formatFloatValue with comptime_float" {
@@ -2542,19 +2542,19 @@ test "formatType max_depth" {
     var buf: [1000]u8 = undefined;
     var fbs = std.io.fixedBufferStream(&buf);
     try formatType(inst, "", FormatOptions{}, fbs.writer(), 0);
-    try std.testing.expect(mem.eql(u8, fbs.getWritten(), "fmt.test.formatType max_depth.S{ ... }"));
+    try std.testing.expectEqualStrings("fmt.test.formatType max_depth.S{ ... }", fbs.getWritten());
 
     fbs.reset();
     try formatType(inst, "", FormatOptions{}, fbs.writer(), 1);
-    try std.testing.expect(mem.eql(u8, fbs.getWritten(), "fmt.test.formatType max_depth.S{ .a = fmt.test.formatType max_depth.S{ ... }, .tu = fmt.test.formatType max_depth.TU{ ... }, .e = fmt.test.formatType max_depth.E.Two, .vec = (10.200,2.220) }"));
+    try std.testing.expectEqualStrings("fmt.test.formatType max_depth.S{ .a = fmt.test.formatType max_depth.S{ ... }, .tu = fmt.test.formatType max_depth.TU{ ... }, .e = fmt.test.formatType max_depth.E.Two, .vec = (10.200,2.220) }", fbs.getWritten());
 
     fbs.reset();
     try formatType(inst, "", FormatOptions{}, fbs.writer(), 2);
-    try std.testing.expect(mem.eql(u8, fbs.getWritten(), "fmt.test.formatType max_depth.S{ .a = fmt.test.formatType max_depth.S{ .a = fmt.test.formatType max_depth.S{ ... }, .tu = fmt.test.formatType max_depth.TU{ ... }, .e = fmt.test.formatType max_depth.E.Two, .vec = (10.200,2.220) }, .tu = fmt.test.formatType max_depth.TU{ .ptr = fmt.test.formatType max_depth.TU{ ... } }, .e = fmt.test.formatType max_depth.E.Two, .vec = (10.200,2.220) }"));
+    try std.testing.expectEqualStrings("fmt.test.formatType max_depth.S{ .a = fmt.test.formatType max_depth.S{ .a = fmt.test.formatType max_depth.S{ ... }, .tu = fmt.test.formatType max_depth.TU{ ... }, .e = fmt.test.formatType max_depth.E.Two, .vec = (10.200,2.220) }, .tu = fmt.test.formatType max_depth.TU{ .ptr = fmt.test.formatType max_depth.TU{ ... } }, .e = fmt.test.formatType max_depth.E.Two, .vec = (10.200,2.220) }", fbs.getWritten());
 
     fbs.reset();
     try formatType(inst, "", FormatOptions{}, fbs.writer(), 3);
-    try std.testing.expect(mem.eql(u8, fbs.getWritten(), "fmt.test.formatType max_depth.S{ .a = fmt.test.formatType max_depth.S{ .a = fmt.test.formatType max_depth.S{ .a = fmt.test.formatType max_depth.S{ ... }, .tu = fmt.test.formatType max_depth.TU{ ... }, .e = fmt.test.formatType max_depth.E.Two, .vec = (10.200,2.220) }, .tu = fmt.test.formatType max_depth.TU{ .ptr = fmt.test.formatType max_depth.TU{ ... } }, .e = fmt.test.formatType max_depth.E.Two, .vec = (10.200,2.220) }, .tu = fmt.test.formatType max_depth.TU{ .ptr = fmt.test.formatType max_depth.TU{ .ptr = fmt.test.formatType max_depth.TU{ ... } } }, .e = fmt.test.formatType max_depth.E.Two, .vec = (10.200,2.220) }"));
+    try std.testing.expectEqualStrings("fmt.test.formatType max_depth.S{ .a = fmt.test.formatType max_depth.S{ .a = fmt.test.formatType max_depth.S{ .a = fmt.test.formatType max_depth.S{ ... }, .tu = fmt.test.formatType max_depth.TU{ ... }, .e = fmt.test.formatType max_depth.E.Two, .vec = (10.200,2.220) }, .tu = fmt.test.formatType max_depth.TU{ .ptr = fmt.test.formatType max_depth.TU{ ... } }, .e = fmt.test.formatType max_depth.E.Two, .vec = (10.200,2.220) }, .tu = fmt.test.formatType max_depth.TU{ .ptr = fmt.test.formatType max_depth.TU{ .ptr = fmt.test.formatType max_depth.TU{ ... } } }, .e = fmt.test.formatType max_depth.E.Two, .vec = (10.200,2.220) }", fbs.getWritten());
 }
 
 test "positional" {
diff --git a/lib/std/fs/Dir.zig b/lib/std/fs/Dir.zig
index 89b1d18b9c..08c23d03b5 100644
--- a/lib/std/fs/Dir.zig
+++ b/lib/std/fs/Dir.zig
@@ -1104,27 +1104,29 @@ pub fn createFileW(self: Dir, sub_path_w: []const u16, flags: File.CreateFlags)
     return file;
 }
 
+pub const MakeError = posix.MakeDirError;
+
 /// Creates a single directory with a relative or absolute path.
 /// To create multiple directories to make an entire path, see `makePath`.
 /// To operate on only absolute paths, see `makeDirAbsolute`.
 /// On Windows, `sub_path` should be encoded as [WTF-8](https://simonsapin.github.io/wtf-8/).
 /// On WASI, `sub_path` should be encoded as valid UTF-8.
 /// On other platforms, `sub_path` is an opaque sequence of bytes with no particular encoding.
-pub fn makeDir(self: Dir, sub_path: []const u8) !void {
+pub fn makeDir(self: Dir, sub_path: []const u8) MakeError!void {
     try posix.mkdirat(self.fd, sub_path, default_mode);
 }
 
 /// Same as `makeDir`, but `sub_path` is null-terminated.
 /// To create multiple directories to make an entire path, see `makePath`.
 /// To operate on only absolute paths, see `makeDirAbsoluteZ`.
-pub fn makeDirZ(self: Dir, sub_path: [*:0]const u8) !void {
+pub fn makeDirZ(self: Dir, sub_path: [*:0]const u8) MakeError!void {
     try posix.mkdiratZ(self.fd, sub_path, default_mode);
 }
 
 /// Creates a single directory with a relative or absolute null-terminated WTF-16 LE-encoded path.
 /// To create multiple directories to make an entire path, see `makePath`.
 /// To operate on only absolute paths, see `makeDirAbsoluteW`.
-pub fn makeDirW(self: Dir, sub_path: [*:0]const u16) !void {
+pub fn makeDirW(self: Dir, sub_path: [*:0]const u16) MakeError!void {
     try posix.mkdiratW(self.fd, sub_path, default_mode);
 }
 
@@ -1144,7 +1146,7 @@ pub fn makeDirW(self: Dir, sub_path: [*:0]const u16) !void {
 /// - On other platforms, `..` are not resolved before the path is passed to `mkdirat`,
 ///   meaning a `sub_path` like "first/../second" will create both a `./first`
 ///   and a `./second` directory.
-pub fn makePath(self: Dir, sub_path: []const u8) !void {
+pub fn makePath(self: Dir, sub_path: []const u8) (MakeError || StatFileError)!void {
     var it = try fs.path.componentIterator(sub_path);
     var component = it.last() orelse return;
     while (true) {
@@ -1178,7 +1180,7 @@ pub fn makePath(self: Dir, sub_path: []const u8) !void {
 /// This function is not atomic, and if it returns an error, the file system may
 /// have been modified regardless.
 /// `sub_path` should be encoded as [WTF-8](https://simonsapin.github.io/wtf-8/).
-fn makeOpenPathAccessMaskW(self: Dir, sub_path: []const u8, access_mask: u32, no_follow: bool) OpenError!Dir {
+fn makeOpenPathAccessMaskW(self: Dir, sub_path: []const u8, access_mask: u32, no_follow: bool) (MakeError || OpenError || StatFileError)!Dir {
     const w = windows;
     var it = try fs.path.componentIterator(sub_path);
     // If there are no components in the path, then create a dummy component with the full path.
@@ -1198,12 +1200,27 @@ fn makeOpenPathAccessMaskW(self: Dir, sub_path: []const u8, access_mask: u32, no
                 component = it.previous() orelse return e;
                 continue;
             },
+            error.PathAlreadyExists => result: {
+                assert(!is_last);
+                // stat the file and return an error if it's not a directory
+                // this is important because otherwise a dangling symlink
+                // could cause an infinite loop
+                check_dir: {
+                    // workaround for windows, see https://github.com/ziglang/zig/issues/16738
+                    const fstat = self.statFile(component.path) catch |stat_err| switch (stat_err) {
+                        error.IsDir => break :check_dir,
+                        else => |e| return e,
+                    };
+                    if (fstat.kind != .directory) return error.NotDir;
+                }
+                break :result null;
+            },
             else => |e| return e,
         };
-
-        component = it.next() orelse return result;
         // Don't leak the intermediate file handles
-        result.close();
+        errdefer if (result) |*dir| dir.close();
+
+        component = it.next() orelse return result.?;
     }
 }
 
@@ -1213,7 +1230,7 @@ fn makeOpenPathAccessMaskW(self: Dir, sub_path: []const u8, access_mask: u32, no
 /// On Windows, `sub_path` should be encoded as [WTF-8](https://simonsapin.github.io/wtf-8/).
 /// On WASI, `sub_path` should be encoded as valid UTF-8.
 /// On other platforms, `sub_path` is an opaque sequence of bytes with no particular encoding.
-pub fn makeOpenPath(self: Dir, sub_path: []const u8, open_dir_options: OpenDirOptions) !Dir {
+pub fn makeOpenPath(self: Dir, sub_path: []const u8, open_dir_options: OpenDirOptions) (MakeError || OpenError || StatFileError)!Dir {
     return switch (native_os) {
         .windows => {
             const w = windows;
@@ -1401,7 +1418,7 @@ pub fn openDir(self: Dir, sub_path: []const u8, args: OpenDirOptions) OpenError!
             const sub_path_w = try windows.sliceToPrefixedFileW(self.fd, sub_path);
             return self.openDirW(sub_path_w.span().ptr, args);
         },
-        .wasi => {
+        .wasi => if (!builtin.link_libc) {
             var base: std.os.wasi.rights_t = .{
                 .FD_FILESTAT_GET = true,
                 .FD_FDSTAT_SET_FLAGS = true,
@@ -1446,11 +1463,10 @@ pub fn openDir(self: Dir, sub_path: []const u8, args: OpenDirOptions) OpenError!
             };
             return .{ .fd = fd };
         },
-        else => {
-            const sub_path_c = try posix.toPosixPath(sub_path);
-            return self.openDirZ(&sub_path_c, args);
-        },
+        else => {},
     }
+    const sub_path_c = try posix.toPosixPath(sub_path);
+    return self.openDirZ(&sub_path_c, args);
 }
 
 /// Same as `openDir` except the parameter is null-terminated.
@@ -1460,7 +1476,9 @@ pub fn openDirZ(self: Dir, sub_path_c: [*:0]const u8, args: OpenDirOptions) Open
             const sub_path_w = try windows.cStrToPrefixedFileW(self.fd, sub_path_c);
             return self.openDirW(sub_path_w.span().ptr, args);
         },
-        .wasi => {
+        // Use the libc API when libc is linked because it implements things
+        // such as opening absolute directory paths.
+        .wasi => if (!builtin.link_libc) {
             return openDir(self, mem.sliceTo(sub_path_c, 0), args);
         },
         .haiku => {
@@ -1484,19 +1502,27 @@ pub fn openDirZ(self: Dir, sub_path_c: [*:0]const u8, args: OpenDirOptions) Open
                 else => |err| return posix.unexpectedErrno(err),
             }
         },
-        else => {
-            var symlink_flags: posix.O = .{
-                .ACCMODE = .RDONLY,
-                .NOFOLLOW = args.no_follow,
-                .DIRECTORY = true,
-                .CLOEXEC = true,
-            };
-            if (@hasField(posix.O, "PATH") and !args.iterate)
-                symlink_flags.PATH = true;
-
-            return self.openDirFlagsZ(sub_path_c, symlink_flags);
-        },
+        else => {},
     }
+
+    var symlink_flags: posix.O = switch (native_os) {
+        .wasi => .{
+            .read = true,
+            .NOFOLLOW = args.no_follow,
+            .DIRECTORY = true,
+        },
+        else => .{
+            .ACCMODE = .RDONLY,
+            .NOFOLLOW = args.no_follow,
+            .DIRECTORY = true,
+            .CLOEXEC = true,
+        },
+    };
+
+    if (@hasField(posix.O, "PATH") and !args.iterate)
+        symlink_flags.PATH = true;
+
+    return self.openDirFlagsZ(sub_path_c, symlink_flags);
 }
 
 /// Same as `openDir` except the path parameter is WTF-16 LE encoded, NT-prefixed.
@@ -1507,10 +1533,17 @@ pub fn openDirW(self: Dir, sub_path_w: [*:0]const u16, args: OpenDirOptions) Ope
     const base_flags = w.STANDARD_RIGHTS_READ | w.FILE_READ_ATTRIBUTES | w.FILE_READ_EA |
         w.SYNCHRONIZE | w.FILE_TRAVERSE;
     const flags: u32 = if (args.iterate) base_flags | w.FILE_LIST_DIRECTORY else base_flags;
-    const dir = try self.makeOpenDirAccessMaskW(sub_path_w, flags, .{
+    const dir = self.makeOpenDirAccessMaskW(sub_path_w, flags, .{
         .no_follow = args.no_follow,
         .create_disposition = w.FILE_OPEN,
-    });
+    }) catch |err| switch (err) {
+        error.ReadOnlyFileSystem => unreachable,
+        error.DiskQuota => unreachable,
+        error.NoSpaceLeft => unreachable,
+        error.PathAlreadyExists => unreachable,
+        error.LinkQuotaExceeded => unreachable,
+        else => |e| return e,
+    };
     return dir;
 }
 
@@ -1535,7 +1568,7 @@ const MakeOpenDirAccessMaskWOptions = struct {
     create_disposition: u32,
 };
 
-fn makeOpenDirAccessMaskW(self: Dir, sub_path_w: [*:0]const u16, access_mask: u32, flags: MakeOpenDirAccessMaskWOptions) OpenError!Dir {
+fn makeOpenDirAccessMaskW(self: Dir, sub_path_w: [*:0]const u16, access_mask: u32, flags: MakeOpenDirAccessMaskWOptions) (MakeError || OpenError)!Dir {
     const w = windows;
 
     var result = Dir{
@@ -1576,6 +1609,7 @@ fn makeOpenDirAccessMaskW(self: Dir, sub_path_w: [*:0]const u16, access_mask: u3
         .SUCCESS => return result,
         .OBJECT_NAME_INVALID => return error.BadPathName,
         .OBJECT_NAME_NOT_FOUND => return error.FileNotFound,
+        .OBJECT_NAME_COLLISION => return error.PathAlreadyExists,
         .OBJECT_PATH_NOT_FOUND => return error.FileNotFound,
         .NOT_A_DIRECTORY => return error.NotDir,
         // This can happen if the directory has 'List folder contents' permission set to 'Deny'
diff --git a/lib/std/heap/PageAllocator.zig b/lib/std/heap/PageAllocator.zig
index 67cafe48d9..4188c25528 100644
--- a/lib/std/heap/PageAllocator.zig
+++ b/lib/std/heap/PageAllocator.zig
@@ -19,18 +19,22 @@ fn alloc(_: *anyopaque, n: usize, log2_align: u8, ra: usize) ?[*]u8 {
     _ = log2_align;
     assert(n > 0);
     if (n > maxInt(usize) - (mem.page_size - 1)) return null;
-    const aligned_len = mem.alignForward(usize, n, mem.page_size);
 
     if (native_os == .windows) {
         const addr = windows.VirtualAlloc(
             null,
-            aligned_len,
+
+            // VirtualAlloc will round the length to a multiple of page size.
+            // VirtualAlloc docs: If the lpAddress parameter is NULL, this value is rounded up to the next page boundary
+            n,
+
             windows.MEM_COMMIT | windows.MEM_RESERVE,
             windows.PAGE_READWRITE,
         ) catch return null;
         return @ptrCast(addr);
     }
 
+    const aligned_len = mem.alignForward(usize, n, mem.page_size);
     const hint = @atomicLoad(@TypeOf(std.heap.next_mmap_addr_hint), &std.heap.next_mmap_addr_hint, .unordered);
     const slice = posix.mmap(
         hint,
diff --git a/lib/std/heap/general_purpose_allocator.zig b/lib/std/heap/general_purpose_allocator.zig
index 278c2bc264..61e256d290 100644
--- a/lib/std/heap/general_purpose_allocator.zig
+++ b/lib/std/heap/general_purpose_allocator.zig
@@ -297,6 +297,12 @@ pub fn GeneralPurposeAllocator(comptime config: Config) type {
                 const stack_addresses = bucket.stackTracePtr(size_class, slot_index, trace_kind);
                 collectStackTrace(ret_addr, stack_addresses);
             }
+
+            /// Only valid for buckets within `empty_buckets`, and relies on the `alloc_cursor`
+            /// of empty buckets being set to `slot_count` when they are added to `empty_buckets`
+            fn emptyBucketSizeClass(bucket: *BucketHeader) usize {
+                return @divExact(page_size, bucket.alloc_cursor);
+            }
         };
 
         pub fn allocator(self: *Self) Allocator {
@@ -439,15 +445,18 @@ pub fn GeneralPurposeAllocator(comptime config: Config) type {
                     }
                 }
                 // free retained metadata for small allocations
-                var empty_it = self.empty_buckets.inorderIterator();
-                while (empty_it.next()) |node| {
+                while (self.empty_buckets.getMin()) |node| {
+                    // remove the node from the tree before destroying it
+                    var entry = self.empty_buckets.getEntryForExisting(node);
+                    entry.set(null);
+
                     var bucket = node.key;
                     if (config.never_unmap) {
                         // free page that was intentionally leaked by never_unmap
                         self.backing_allocator.free(bucket.page[0..page_size]);
                     }
                     // alloc_cursor was set to slot count when bucket added to empty_buckets
-                    self.freeBucket(bucket, @divExact(page_size, bucket.alloc_cursor));
+                    self.freeBucket(bucket, bucket.emptyBucketSizeClass());
                     self.bucket_node_pool.destroy(node);
                 }
                 self.empty_buckets.root = null;
@@ -726,6 +735,7 @@ pub fn GeneralPurposeAllocator(comptime config: Config) type {
                     if (!self.large_allocations.contains(@intFromPtr(old_mem.ptr))) {
                         // object not in active buckets or a large allocation, so search empty buckets
                         if (searchBucket(&self.empty_buckets, @intFromPtr(old_mem.ptr), null)) |bucket| {
+                            size_class = bucket.emptyBucketSizeClass();
                             // bucket is empty so is_used below will always be false and we exit there
                             break :blk bucket;
                         } else {
@@ -844,6 +854,7 @@ pub fn GeneralPurposeAllocator(comptime config: Config) type {
                     if (!self.large_allocations.contains(@intFromPtr(old_mem.ptr))) {
                         // object not in active buckets or a large allocation, so search empty buckets
                         if (searchBucket(&self.empty_buckets, @intFromPtr(old_mem.ptr), null)) |bucket| {
+                            size_class = bucket.emptyBucketSizeClass();
                             // bucket is empty so is_used below will always be false and we exit there
                             break :blk bucket;
                         } else {
@@ -1418,6 +1429,23 @@ test "double frees" {
     try std.testing.expect(!gpa.large_allocations.contains(@intFromPtr(large.ptr)));
 }
 
+test "empty bucket size class" {
+    const GPA = GeneralPurposeAllocator(.{ .safety = true, .never_unmap = true, .retain_metadata = true });
+    var gpa = GPA{};
+    defer std.testing.expect(gpa.deinit() == .ok) catch @panic("leak");
+    const allocator = gpa.allocator();
+
+    // allocate and free to create an empty bucket
+    const size_class: usize = @as(usize, 1) << 6;
+    const small = try allocator.alloc(u8, size_class);
+    allocator.free(small);
+
+    // the metadata tracking system relies on alloc_cursor of empty buckets
+    // being set to the slot count so that we can get back the size class.
+    const empty_bucket = GPA.searchBucket(&gpa.empty_buckets, @intFromPtr(small.ptr), null).?;
+    try std.testing.expect(empty_bucket.emptyBucketSizeClass() == size_class);
+}
+
 test "bug 9995 fix, large allocs count requested size not backing size" {
     // with AtLeast, buffer likely to be larger than requested, especially when shrinking
     var gpa = GeneralPurposeAllocator(.{ .enable_memory_limit = true }){};
@@ -1430,3 +1458,19 @@ test "bug 9995 fix, large allocs count requested size not backing size" {
     buf = try allocator.realloc(buf, 2);
     try std.testing.expect(gpa.total_requested_bytes == 2);
 }
+
+test "retain metadata and never unmap" {
+    var gpa = std.heap.GeneralPurposeAllocator(.{
+        .safety = true,
+        .never_unmap = true,
+        .retain_metadata = true,
+    }){};
+    defer std.debug.assert(gpa.deinit() == .ok);
+    const allocator = gpa.allocator();
+
+    const alloc = try allocator.alloc(u8, 8);
+    allocator.free(alloc);
+
+    const alloc2 = try allocator.alloc(u8, 8);
+    allocator.free(alloc2);
+}
diff --git a/lib/std/io/tty.zig b/lib/std/io/tty.zig
index c02e371440..baf54a1fdf 100644
--- a/lib/std/io/tty.zig
+++ b/lib/std/io/tty.zig
@@ -70,7 +70,12 @@ pub const Config = union(enum) {
         reset_attributes: u16,
     };
 
-    pub fn setColor(conf: Config, out_stream: anytype, color: Color) !void {
+    pub fn setColor(
+        conf: Config,
+        writer: anytype,
+        color: Color,
+    ) (@typeInfo(@TypeOf(writer.writeAll(""))).ErrorUnion.error_set ||
+        windows.SetConsoleTextAttributeError)!void {
         nosuspend switch (conf) {
             .no_color => return,
             .escape_codes => {
@@ -95,7 +100,7 @@ pub const Config = union(enum) {
                     .dim => "\x1b[2m",
                     .reset => "\x1b[0m",
                 };
-                try out_stream.writeAll(color_string);
+                try writer.writeAll(color_string);
             },
             .windows_api => |ctx| if (native_os == .windows) {
                 const attributes = switch (color) {
diff --git a/lib/std/math.zig b/lib/std/math.zig
index 858e9243bf..f468136a83 100644
--- a/lib/std/math.zig
+++ b/lib/std/math.zig
@@ -52,6 +52,7 @@ pub const floatTrueMin = @import("math/float.zig").floatTrueMin;
 pub const floatMin = @import("math/float.zig").floatMin;
 pub const floatMax = @import("math/float.zig").floatMax;
 pub const floatEps = @import("math/float.zig").floatEps;
+pub const floatEpsAt = @import("math/float.zig").floatEpsAt;
 pub const inf = @import("math/float.zig").inf;
 pub const nan = @import("math/float.zig").nan;
 pub const snan = @import("math/float.zig").snan;
diff --git a/lib/std/math/float.zig b/lib/std/math/float.zig
index f8f04e217c..1d19fdc57c 100644
--- a/lib/std/math/float.zig
+++ b/lib/std/math/float.zig
@@ -94,6 +94,19 @@ pub inline fn floatEps(comptime T: type) T {
     return reconstructFloat(T, -floatFractionalBits(T), mantissaOne(T));
 }
 
+/// Returns the local epsilon of floating point type T.
+pub inline fn floatEpsAt(comptime T: type, x: T) T {
+    switch (@typeInfo(T)) {
+        .Float => |F| {
+            const U: type = @Type(.{ .Int = .{ .signedness = .unsigned, .bits = F.bits } });
+            const u: U = @bitCast(x);
+            const y: T = @bitCast(u ^ 1);
+            return @abs(x - y);
+        },
+        else => @compileError("floatEpsAt only supports floats"),
+    }
+}
+
 /// Returns the value inf for floating point type T.
 pub inline fn inf(comptime T: type) T {
     return reconstructFloat(T, floatExponentMax(T) + 1, mantissaOne(T));
diff --git a/lib/std/math/hypot.zig b/lib/std/math/hypot.zig
index c0bfabca1c..cc0dc17ab1 100644
--- a/lib/std/math/hypot.zig
+++ b/lib/std/math/hypot.zig
@@ -1,13 +1,14 @@
-// Ported from musl, which is licensed under the MIT license:
-// https://git.musl-libc.org/cgit/musl/tree/COPYRIGHT
-//
-// https://git.musl-libc.org/cgit/musl/tree/src/math/hypotf.c
-// https://git.musl-libc.org/cgit/musl/tree/src/math/hypot.c
-
 const std = @import("../std.zig");
 const math = std.math;
 const expect = std.testing.expect;
-const maxInt = std.math.maxInt;
+const isNan = math.isNan;
+const isInf = math.isInf;
+const inf = math.inf;
+const nan = math.nan;
+const floatEpsAt = math.floatEpsAt;
+const floatEps = math.floatEps;
+const floatMin = math.floatMin;
+const floatMax = math.floatMax;
 
 /// Returns sqrt(x * x + y * y), avoiding unnecessary overflow and underflow.
 ///
@@ -15,162 +16,116 @@ const maxInt = std.math.maxInt;
 ///
 /// |   x   |   y   | hypot |
 /// |-------|-------|-------|
-/// | +inf  |  num  | +inf  |
-/// |  num  | +-inf | +inf  |
-/// |  nan  |  any  |  nan  |
-/// |  any  |  nan  |  nan  |
+/// | +-inf |  any  | +inf  |
+/// |  any  | +-inf | +inf  |
+/// |  nan  |  fin  |  nan  |
+/// |  fin  |  nan  |  nan  |
 pub fn hypot(x: anytype, y: anytype) @TypeOf(x, y) {
     const T = @TypeOf(x, y);
-    return switch (T) {
-        f32 => hypot32(x, y),
-        f64 => hypot64(x, y),
+    switch (@typeInfo(T)) {
+        .Float => {},
+        .ComptimeFloat => return @sqrt(x * x + y * y),
         else => @compileError("hypot not implemented for " ++ @typeName(T)),
-    };
+    }
+    const lower = @sqrt(floatMin(T));
+    const upper = @sqrt(floatMax(T) / 2);
+    const incre = @sqrt(floatEps(T) / 2);
+    const scale = floatEpsAt(T, incre);
+    const hypfn = if (emulateFma(T)) hypotUnfused else hypotFused;
+    var major: T = x;
+    var minor: T = y;
+    if (isInf(major) or isInf(minor)) return inf(T);
+    if (isNan(major) or isNan(minor)) return nan(T);
+    if (T == f16) return @floatCast(@sqrt(@mulAdd(f32, x, x, @as(f32, y) * y)));
+    if (T == f32) return @floatCast(@sqrt(@mulAdd(f64, x, x, @as(f64, y) * y)));
+    major = @abs(major);
+    minor = @abs(minor);
+    if (minor > major) {
+        const tempo = major;
+        major = minor;
+        minor = tempo;
+    }
+    if (major * incre >= minor) return major;
+    if (major > upper) return hypfn(T, major * scale, minor * scale) / scale;
+    if (minor < lower) return hypfn(T, major / scale, minor / scale) * scale;
+    return hypfn(T, major, minor);
 }
 
-fn hypot32(x: f32, y: f32) f32 {
-    var ux = @as(u32, @bitCast(x));
-    var uy = @as(u32, @bitCast(y));
-
-    ux &= maxInt(u32) >> 1;
-    uy &= maxInt(u32) >> 1;
-    if (ux < uy) {
-        const tmp = ux;
-        ux = uy;
-        uy = tmp;
-    }
-
-    var xx = @as(f32, @bitCast(ux));
-    var yy = @as(f32, @bitCast(uy));
-    if (uy == 0xFF << 23) {
-        return yy;
-    }
-    if (ux >= 0xFF << 23 or uy == 0 or ux - uy >= (25 << 23)) {
-        return xx + yy;
-    }
-
-    var z: f32 = 1.0;
-    if (ux >= (0x7F + 60) << 23) {
-        z = 0x1.0p90;
-        xx *= 0x1.0p-90;
-        yy *= 0x1.0p-90;
-    } else if (uy < (0x7F - 60) << 23) {
-        z = 0x1.0p-90;
-        xx *= 0x1.0p-90;
-        yy *= 0x1.0p-90;
-    }
-
-    return z * @sqrt(@as(f32, @floatCast(@as(f64, x) * x + @as(f64, y) * y)));
+inline fn emulateFma(comptime T: type) bool {
+    // If @mulAdd lowers to the software implementation,
+    // hypotUnfused should be used in place of hypotFused.
+    // This takes an educated guess, but ideally we should
+    // properly detect at comptime when that fallback will
+    // occur.
+    return (T == f128 or T == f80);
 }
 
-fn sq(hi: *f64, lo: *f64, x: f64) void {
-    const split: f64 = 0x1.0p27 + 1.0;
-    const xc = x * split;
-    const xh = x - xc + xc;
-    const xl = x - xh;
-    hi.* = x * x;
-    lo.* = xh * xh - hi.* + 2 * xh * xl + xl * xl;
+inline fn hypotFused(comptime F: type, x: F, y: F) F {
+    const r = @sqrt(@mulAdd(F, x, x, y * y));
+    const rr = r * r;
+    const xx = x * x;
+    const z = @mulAdd(F, -y, y, rr - xx) + @mulAdd(F, r, r, -rr) - @mulAdd(F, x, x, -xx);
+    return r - z / (2 * r);
 }
 
-fn hypot64(x: f64, y: f64) f64 {
-    var ux = @as(u64, @bitCast(x));
-    var uy = @as(u64, @bitCast(y));
-
-    ux &= maxInt(u64) >> 1;
-    uy &= maxInt(u64) >> 1;
-    if (ux < uy) {
-        const tmp = ux;
-        ux = uy;
-        uy = tmp;
+inline fn hypotUnfused(comptime F: type, x: F, y: F) F {
+    const r = @sqrt(x * x + y * y);
+    if (r <= 2 * y) { // 30deg or steeper
+        const dx = r - y;
+        const z = x * (2 * dx - x) + (dx - 2 * (x - y)) * dx;
+        return r - z / (2 * r);
+    } else { // shallower than 30 deg
+        const dy = r - x;
+        const z = 2 * dy * (x - 2 * y) + (4 * dy - y) * y + dy * dy;
+        return r - z / (2 * r);
     }
-
-    const ex = ux >> 52;
-    const ey = uy >> 52;
-    var xx = @as(f64, @bitCast(ux));
-    var yy = @as(f64, @bitCast(uy));
-
-    // hypot(inf, nan) == inf
-    if (ey == 0x7FF) {
-        return yy;
-    }
-    if (ex == 0x7FF or uy == 0) {
-        return xx;
-    }
-
-    // hypot(x, y) ~= x + y * y / x / 2 with inexact for small y/x
-    if (ex - ey > 64) {
-        return xx + yy;
-    }
-
-    var z: f64 = 1;
-    if (ex > 0x3FF + 510) {
-        z = 0x1.0p700;
-        xx *= 0x1.0p-700;
-        yy *= 0x1.0p-700;
-    } else if (ey < 0x3FF - 450) {
-        z = 0x1.0p-700;
-        xx *= 0x1.0p700;
-        yy *= 0x1.0p700;
-    }
-
-    var hx: f64 = undefined;
-    var lx: f64 = undefined;
-    var hy: f64 = undefined;
-    var ly: f64 = undefined;
-
-    sq(&hx, &lx, x);
-    sq(&hy, &ly, y);
-
-    return z * @sqrt(ly + lx + hy + hx);
 }
 
+const hypot_test_cases = .{
+    .{ 0.0, -1.2, 1.2 },
+    .{ 0.2, -0.34, 0.3944616584663203993612799816649560759946493601889826495362 },
+    .{ 0.8923, 2.636890, 2.7837722899152509525110650481670176852603253522923737962880 },
+    .{ 1.5, 5.25, 5.4600824169603887033229768686452745953332522619323580787836 },
+    .{ 37.45, 159.835, 164.16372840856167640478217141034363907565754072954443805164 },
+    .{ 89.123, 382.028905, 392.28687638576315875933966414927490685367196874260165618371 },
+    .{ 123123.234375, 529428.707813, 543556.88524707706887251269205923830745438413088753096759371 },
+};
+
 test hypot {
-    const x32: f32 = 0.0;
-    const y32: f32 = -1.2;
-    const x64: f64 = 0.0;
-    const y64: f64 = -1.2;
-    try expect(hypot(x32, y32) == hypot32(0.0, -1.2));
-    try expect(hypot(x64, y64) == hypot64(0.0, -1.2));
+    try expect(hypot(0.3, 0.4) == 0.5);
 }
 
-test hypot32 {
-    const epsilon = 0.000001;
-
-    try expect(math.approxEqAbs(f32, hypot32(0.0, -1.2), 1.2, epsilon));
-    try expect(math.approxEqAbs(f32, hypot32(0.2, -0.34), 0.394462, epsilon));
-    try expect(math.approxEqAbs(f32, hypot32(0.8923, 2.636890), 2.783772, epsilon));
-    try expect(math.approxEqAbs(f32, hypot32(1.5, 5.25), 5.460083, epsilon));
-    try expect(math.approxEqAbs(f32, hypot32(37.45, 159.835), 164.163742, epsilon));
-    try expect(math.approxEqAbs(f32, hypot32(89.123, 382.028905), 392.286865, epsilon));
-    try expect(math.approxEqAbs(f32, hypot32(123123.234375, 529428.707813), 543556.875, epsilon));
+test "hypot.correct" {
+    inline for (.{ f16, f32, f64, f128 }) |T| {
+        inline for (hypot_test_cases) |v| {
+            const a: T, const b: T, const c: T = v;
+            try expect(math.approxEqRel(T, hypot(a, b), c, @sqrt(floatEps(T))));
+        }
+    }
 }
 
-test hypot64 {
-    const epsilon = 0.000001;
-
-    try expect(math.approxEqAbs(f64, hypot64(0.0, -1.2), 1.2, epsilon));
-    try expect(math.approxEqAbs(f64, hypot64(0.2, -0.34), 0.394462, epsilon));
-    try expect(math.approxEqAbs(f64, hypot64(0.8923, 2.636890), 2.783772, epsilon));
-    try expect(math.approxEqAbs(f64, hypot64(1.5, 5.25), 5.460082, epsilon));
-    try expect(math.approxEqAbs(f64, hypot64(37.45, 159.835), 164.163728, epsilon));
-    try expect(math.approxEqAbs(f64, hypot64(89.123, 382.028905), 392.286876, epsilon));
-    try expect(math.approxEqAbs(f64, hypot64(123123.234375, 529428.707813), 543556.885247, epsilon));
+test "hypot.precise" {
+    inline for (.{ f16, f32, f64 }) |T| { // f128 seems to be 5 ulp
+        inline for (hypot_test_cases) |v| {
+            const a: T, const b: T, const c: T = v;
+            try expect(math.approxEqRel(T, hypot(a, b), c, floatEps(T)));
+        }
+    }
 }
 
-test "hypot32.special" {
-    try expect(math.isPositiveInf(hypot32(math.inf(f32), 0.0)));
-    try expect(math.isPositiveInf(hypot32(-math.inf(f32), 0.0)));
-    try expect(math.isPositiveInf(hypot32(0.0, math.inf(f32))));
-    try expect(math.isPositiveInf(hypot32(0.0, -math.inf(f32))));
-    try expect(math.isNan(hypot32(math.nan(f32), 0.0)));
-    try expect(math.isNan(hypot32(0.0, math.nan(f32))));
-}
+test "hypot.special" {
+    inline for (.{ f16, f32, f64, f128 }) |T| {
+        try expect(math.isNan(hypot(nan(T), 0.0)));
+        try expect(math.isNan(hypot(0.0, nan(T))));
 
-test "hypot64.special" {
-    try expect(math.isPositiveInf(hypot64(math.inf(f64), 0.0)));
-    try expect(math.isPositiveInf(hypot64(-math.inf(f64), 0.0)));
-    try expect(math.isPositiveInf(hypot64(0.0, math.inf(f64))));
-    try expect(math.isPositiveInf(hypot64(0.0, -math.inf(f64))));
-    try expect(math.isNan(hypot64(math.nan(f64), 0.0)));
-    try expect(math.isNan(hypot64(0.0, math.nan(f64))));
+        try expect(math.isPositiveInf(hypot(inf(T), 0.0)));
+        try expect(math.isPositiveInf(hypot(0.0, inf(T))));
+        try expect(math.isPositiveInf(hypot(inf(T), nan(T))));
+        try expect(math.isPositiveInf(hypot(nan(T), inf(T))));
+
+        try expect(math.isPositiveInf(hypot(-inf(T), 0.0)));
+        try expect(math.isPositiveInf(hypot(0.0, -inf(T))));
+        try expect(math.isPositiveInf(hypot(-inf(T), nan(T))));
+        try expect(math.isPositiveInf(hypot(nan(T), -inf(T))));
+    }
 }
diff --git a/lib/std/os/linux.zig b/lib/std/os/linux.zig
index 69cef35e98..c294009d91 100644
--- a/lib/std/os/linux.zig
+++ b/lib/std/os/linux.zig
@@ -1893,7 +1893,7 @@ pub fn sched_setaffinity(pid: pid_t, set: *const cpu_set_t) !void {
 
     switch (std.os.errno(rc)) {
         .SUCCESS => return,
-        else => |err| return std.os.unexpectedErrno(err),
+        else => |err| return std.posix.unexpectedErrno(err),
     }
 }
 
@@ -5918,8 +5918,8 @@ pub const SIOCGIFINDEX = 0x8933;
 pub const IFNAMESIZE = 16;
 
 pub const ifmap = extern struct {
-    mem_start: u32,
-    mem_end: u32,
+    mem_start: usize,
+    mem_end: usize,
     base_addr: u16,
     irq: u8,
     dma: u8,
diff --git a/lib/std/os/linux/IoUring.zig b/lib/std/os/linux/IoUring.zig
index 263321bb65..4f53fa009f 100644
--- a/lib/std/os/linux/IoUring.zig
+++ b/lib/std/os/linux/IoUring.zig
@@ -1559,7 +1559,7 @@ pub fn setup_buf_ring(fd: posix.fd_t, entries: u16, group_id: u16) !*align(mem.p
     if (entries == 0 or entries > 1 << 15) return error.EntriesNotInRange;
     if (!std.math.isPowerOfTwo(entries)) return error.EntriesNotPowerOfTwo;
 
-    const mmap_size = entries * @sizeOf(linux.io_uring_buf);
+    const mmap_size = @as(usize, entries) * @sizeOf(linux.io_uring_buf);
     const mmap = try posix.mmap(
         null,
         mmap_size,
@@ -3503,6 +3503,10 @@ test "accept multishot" {
 }
 
 test "accept/connect/send_zc/recv" {
+    if (true) {
+        // https://github.com/ziglang/zig/issues/20212
+        return error.SkipZigTest;
+    }
     try skipKernelLessThan(.{ .major = 6, .minor = 0, .patch = 0 });
 
     var ring = IoUring.init(16, 0) catch |err| switch (err) {
diff --git a/lib/std/os/linux/bpf.zig b/lib/std/os/linux/bpf.zig
index 5e02485b15..61c704fce9 100644
--- a/lib/std/os/linux/bpf.zig
+++ b/lib/std/os/linux/bpf.zig
@@ -1,6 +1,6 @@
 const std = @import("../../std.zig");
 const errno = linux.E.init;
-const unexpectedErrno = std.os.unexpectedErrno;
+const unexpectedErrno = std.posix.unexpectedErrno;
 const expectEqual = std.testing.expectEqual;
 const expectError = std.testing.expectError;
 const expect = std.testing.expect;
diff --git a/lib/std/os/wasi.zig b/lib/std/os/wasi.zig
index d0f8bdbb66..2c7d0d3272 100644
--- a/lib/std/os/wasi.zig
+++ b/lib/std/os/wasi.zig
@@ -7,14 +7,16 @@ const std = @import("std");
 const assert = std.debug.assert;
 
 comptime {
-    assert(@alignOf(i8) == 1);
-    assert(@alignOf(u8) == 1);
-    assert(@alignOf(i16) == 2);
-    assert(@alignOf(u16) == 2);
-    assert(@alignOf(i32) == 4);
-    assert(@alignOf(u32) == 4);
-    // assert(@alignOf(i64) == 8);
-    // assert(@alignOf(u64) == 8);
+    if (builtin.os.tag == .wasi) {
+        assert(@alignOf(i8) == 1);
+        assert(@alignOf(u8) == 1);
+        assert(@alignOf(i16) == 2);
+        assert(@alignOf(u16) == 2);
+        assert(@alignOf(i32) == 4);
+        assert(@alignOf(u32) == 4);
+        assert(@alignOf(i64) == 8);
+        assert(@alignOf(u64) == 8);
+    }
 }
 
 pub const iovec_t = std.posix.iovec;
diff --git a/lib/std/os/windows.zig b/lib/std/os/windows.zig
index 27a7b8a351..56940b4580 100644
--- a/lib/std/os/windows.zig
+++ b/lib/std/os/windows.zig
@@ -304,7 +304,7 @@ pub fn CreateEventEx(attributes: ?*SECURITY_ATTRIBUTES, name: []const u8, flags:
     return CreateEventExW(attributes, nameW.span().ptr, flags, desired_access);
 }
 
-pub fn CreateEventExW(attributes: ?*SECURITY_ATTRIBUTES, nameW: [*:0]const u16, flags: DWORD, desired_access: DWORD) !HANDLE {
+pub fn CreateEventExW(attributes: ?*SECURITY_ATTRIBUTES, nameW: ?LPCWSTR, flags: DWORD, desired_access: DWORD) !HANDLE {
     const handle = kernel32.CreateEventExW(attributes, nameW, flags, desired_access);
     if (handle) |h| {
         return h;
@@ -1368,6 +1368,61 @@ pub fn GetFinalPathNameByHandle(
                         return error.BadPathName;
                     }
 
+                    return out_buffer[0..total_len];
+                } else if (mountmgrIsVolumeName(symlink)) {
+                    // If the symlink is a volume GUID like \??\Volume{383da0b0-717f-41b6-8c36-00500992b58d},
+                    // then it is a volume mounted as a path rather than a drive letter. We need to
+                    // query the mount manager again to get the DOS path for the volume.
+
+                    // 49 is the maximum length accepted by mountmgrIsVolumeName
+                    const vol_input_size = @sizeOf(MOUNTMGR_TARGET_NAME) + (49 * 2);
+                    var vol_input_buf: [vol_input_size]u8 align(@alignOf(MOUNTMGR_TARGET_NAME)) = [_]u8{0} ** vol_input_size;
+                    // Note: If the path exceeds MAX_PATH, the Disk Management GUI doesn't accept the full path,
+                    // and instead if must be specified using a shortened form (e.g. C:\FOO~1\BAR~1\<...>).
+                    // However, just to be sure we can handle any path length, we use PATH_MAX_WIDE here.
+                    const min_output_size = @sizeOf(MOUNTMGR_VOLUME_PATHS) + (PATH_MAX_WIDE * 2);
+                    var vol_output_buf: [min_output_size]u8 align(@alignOf(MOUNTMGR_VOLUME_PATHS)) = undefined;
+
+                    var vol_input_struct: *MOUNTMGR_TARGET_NAME = @ptrCast(&vol_input_buf[0]);
+                    vol_input_struct.DeviceNameLength = @intCast(symlink.len * 2);
+                    @memcpy(@as([*]WCHAR, &vol_input_struct.DeviceName)[0..symlink.len], symlink);
+
+                    DeviceIoControl(mgmt_handle, IOCTL_MOUNTMGR_QUERY_DOS_VOLUME_PATH, &vol_input_buf, &vol_output_buf) catch |err| switch (err) {
+                        error.AccessDenied => return error.Unexpected,
+                        else => |e| return e,
+                    };
+                    const volume_paths_struct: *const MOUNTMGR_VOLUME_PATHS = @ptrCast(&vol_output_buf[0]);
+                    const volume_path = std.mem.sliceTo(@as(
+                        [*]const u16,
+                        &volume_paths_struct.MultiSz,
+                    )[0 .. volume_paths_struct.MultiSzLength / 2], 0);
+
+                    if (out_buffer.len < volume_path.len + file_name_u16.len) return error.NameTooLong;
+
+                    // `out_buffer` currently contains the memory of `file_name_u16`, so it can overlap with where
+                    // we want to place the filename before returning. Here are the possible overlapping cases:
+                    //
+                    // out_buffer:       [filename]
+                    //       dest: [___(a)___] [___(b)___]
+                    //
+                    // In the case of (a), we need to copy forwards, and in the case of (b) we need
+                    // to copy backwards. We also need to do this before copying the volume path because
+                    // it could overwrite the file_name_u16 memory.
+                    const file_name_dest = out_buffer[volume_path.len..][0..file_name_u16.len];
+                    const file_name_byte_offset = @intFromPtr(file_name_u16.ptr) - @intFromPtr(out_buffer.ptr);
+                    const file_name_index = file_name_byte_offset / @sizeOf(u16);
+                    if (volume_path.len > file_name_index)
+                        mem.copyBackwards(u16, file_name_dest, file_name_u16)
+                    else
+                        mem.copyForwards(u16, file_name_dest, file_name_u16);
+                    @memcpy(out_buffer[0..volume_path.len], volume_path);
+                    const total_len = volume_path.len + file_name_u16.len;
+
+                    // Validate that DOS does not contain any spurious nul bytes.
+                    if (mem.indexOfScalar(u16, out_buffer[0..total_len], 0)) |_| {
+                        return error.BadPathName;
+                    }
+
                     return out_buffer[0..total_len];
                 }
             }
@@ -1379,6 +1434,32 @@ pub fn GetFinalPathNameByHandle(
     }
 }
 
+/// Equivalent to the MOUNTMGR_IS_VOLUME_NAME macro in mountmgr.h
+fn mountmgrIsVolumeName(name: []const u16) bool {
+    return (name.len == 48 or (name.len == 49 and name[48] == mem.nativeToLittle(u16, '\\'))) and
+        name[0] == mem.nativeToLittle(u16, '\\') and
+        (name[1] == mem.nativeToLittle(u16, '?') or name[1] == mem.nativeToLittle(u16, '\\')) and
+        name[2] == mem.nativeToLittle(u16, '?') and
+        name[3] == mem.nativeToLittle(u16, '\\') and
+        mem.startsWith(u16, name[4..], std.unicode.utf8ToUtf16LeStringLiteral("Volume{")) and
+        name[19] == mem.nativeToLittle(u16, '-') and
+        name[24] == mem.nativeToLittle(u16, '-') and
+        name[29] == mem.nativeToLittle(u16, '-') and
+        name[34] == mem.nativeToLittle(u16, '-') and
+        name[47] == mem.nativeToLittle(u16, '}');
+}
+
+test mountmgrIsVolumeName {
+    const L = std.unicode.utf8ToUtf16LeStringLiteral;
+    try std.testing.expect(mountmgrIsVolumeName(L("\\\\?\\Volume{383da0b0-717f-41b6-8c36-00500992b58d}")));
+    try std.testing.expect(mountmgrIsVolumeName(L("\\??\\Volume{383da0b0-717f-41b6-8c36-00500992b58d}")));
+    try std.testing.expect(mountmgrIsVolumeName(L("\\\\?\\Volume{383da0b0-717f-41b6-8c36-00500992b58d}\\")));
+    try std.testing.expect(mountmgrIsVolumeName(L("\\??\\Volume{383da0b0-717f-41b6-8c36-00500992b58d}\\")));
+    try std.testing.expect(!mountmgrIsVolumeName(L("\\\\.\\Volume{383da0b0-717f-41b6-8c36-00500992b58d}")));
+    try std.testing.expect(!mountmgrIsVolumeName(L("\\??\\Volume{383da0b0-717f-41b6-8c36-00500992b58d}\\foo")));
+    try std.testing.expect(!mountmgrIsVolumeName(L("\\??\\Volume{383da0b0-717f-41b6-8c36-00500992b58}")));
+}
+
 test GetFinalPathNameByHandle {
     if (builtin.os.tag != .windows)
         return;
@@ -4845,6 +4926,8 @@ pub const SYMLINK_FLAG_RELATIVE: ULONG = 0x1;
 pub const SYMBOLIC_LINK_FLAG_DIRECTORY: DWORD = 0x1;
 pub const SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE: DWORD = 0x2;
 
+pub const MOUNTMGRCONTROLTYPE = 0x0000006D;
+
 pub const MOUNTMGR_MOUNT_POINT = extern struct {
     SymbolicLinkNameOffset: ULONG,
     SymbolicLinkNameLength: USHORT,
@@ -4861,7 +4944,17 @@ pub const MOUNTMGR_MOUNT_POINTS = extern struct {
     NumberOfMountPoints: ULONG,
     MountPoints: [1]MOUNTMGR_MOUNT_POINT,
 };
-pub const IOCTL_MOUNTMGR_QUERY_POINTS: ULONG = 0x6d0008;
+pub const IOCTL_MOUNTMGR_QUERY_POINTS = CTL_CODE(MOUNTMGRCONTROLTYPE, 2, .METHOD_BUFFERED, FILE_ANY_ACCESS);
+
+pub const MOUNTMGR_TARGET_NAME = extern struct {
+    DeviceNameLength: USHORT,
+    DeviceName: [1]WCHAR,
+};
+pub const MOUNTMGR_VOLUME_PATHS = extern struct {
+    MultiSzLength: ULONG,
+    MultiSz: [1]WCHAR,
+};
+pub const IOCTL_MOUNTMGR_QUERY_DOS_VOLUME_PATH = CTL_CODE(MOUNTMGRCONTROLTYPE, 12, .METHOD_BUFFERED, FILE_ANY_ACCESS);
 
 pub const OBJECT_INFORMATION_CLASS = enum(c_int) {
     ObjectBasicInformation = 0,
diff --git a/lib/std/os/windows/kernel32.zig b/lib/std/os/windows/kernel32.zig
index a1ca655ed1..da747647ae 100644
--- a/lib/std/os/windows/kernel32.zig
+++ b/lib/std/os/windows/kernel32.zig
@@ -82,7 +82,7 @@ pub extern "kernel32" fn SetEndOfFile(hFile: HANDLE) callconv(WINAPI) BOOL;
 
 pub extern "kernel32" fn CreateEventExW(
     lpEventAttributes: ?*SECURITY_ATTRIBUTES,
-    lpName: [*:0]const u16,
+    lpName: ?LPCWSTR,
     dwFlags: DWORD,
     dwDesiredAccess: DWORD,
 ) callconv(WINAPI) ?HANDLE;
@@ -243,6 +243,8 @@ pub extern "kernel32" fn GetSystemInfo(lpSystemInfo: *SYSTEM_INFO) callconv(WINA
 pub extern "kernel32" fn GetSystemTimeAsFileTime(*FILETIME) callconv(WINAPI) void;
 pub extern "kernel32" fn IsProcessorFeaturePresent(ProcessorFeature: DWORD) BOOL;
 
+pub extern "kernel32" fn GetSystemDirectoryW(lpBuffer: LPWSTR, uSize: UINT) callconv(WINAPI) UINT;
+
 pub extern "kernel32" fn HeapCreate(flOptions: DWORD, dwInitialSize: SIZE_T, dwMaximumSize: SIZE_T) callconv(WINAPI) ?HANDLE;
 pub extern "kernel32" fn HeapDestroy(hHeap: HANDLE) callconv(WINAPI) BOOL;
 pub extern "kernel32" fn HeapReAlloc(hHeap: HANDLE, dwFlags: DWORD, lpMem: *anyopaque, dwBytes: SIZE_T) callconv(WINAPI) ?*anyopaque;
diff --git a/lib/std/posix.zig b/lib/std/posix.zig
index 857c8dd1e2..5e70159531 100644
--- a/lib/std/posix.zig
+++ b/lib/std/posix.zig
@@ -542,7 +542,7 @@ pub fn reboot(cmd: RebootCommand) RebootError!void {
             ))) {
                 .SUCCESS => {},
                 .PERM => return error.PermissionDenied,
-                else => |err| return std.os.unexpectedErrno(err),
+                else => |err| return std.posix.unexpectedErrno(err),
             }
             switch (cmd) {
                 .CAD_OFF => {},
@@ -717,7 +717,7 @@ pub fn raise(sig: u8) RaiseError!void {
         }
     }
 
-    @compileError("std.os.raise unimplemented for this target");
+    @compileError("std.posix.raise unimplemented for this target");
 }
 
 pub const KillError = error{ ProcessNotFound, PermissionDenied } || UnexpectedError;
@@ -1932,7 +1932,7 @@ pub fn execvpeZ(
 /// See also `getenvZ`.
 pub fn getenv(key: []const u8) ?[:0]const u8 {
     if (native_os == .windows) {
-        @compileError("std.os.getenv is unavailable for Windows because environment strings are in WTF-16 format. See std.process.getEnvVarOwned for a cross-platform API or std.process.getenvW for a Windows-specific API.");
+        @compileError("std.posix.getenv is unavailable for Windows because environment strings are in WTF-16 format. See std.process.getEnvVarOwned for a cross-platform API or std.process.getenvW for a Windows-specific API.");
     }
     if (builtin.link_libc) {
         var ptr = std.c.environ;
@@ -1948,7 +1948,7 @@ pub fn getenv(key: []const u8) ?[:0]const u8 {
         return null;
     }
     if (native_os == .wasi) {
-        @compileError("std.os.getenv is unavailable for WASI. See std.process.getEnvMap or std.process.getEnvVarOwned for a cross-platform API.");
+        @compileError("std.posix.getenv is unavailable for WASI. See std.process.getEnvMap or std.process.getEnvVarOwned for a cross-platform API.");
     }
     // The simplified start logic doesn't populate environ.
     if (std.start.simplified_logic) return null;
@@ -1972,7 +1972,7 @@ pub fn getenvZ(key: [*:0]const u8) ?[:0]const u8 {
         return mem.sliceTo(value, 0);
     }
     if (native_os == .windows) {
-        @compileError("std.os.getenvZ is unavailable for Windows because environment string is in WTF-16 format. See std.process.getEnvVarOwned for cross-platform API or std.process.getenvW for Windows-specific API.");
+        @compileError("std.posix.getenvZ is unavailable for Windows because environment string is in WTF-16 format. See std.process.getEnvVarOwned for cross-platform API or std.process.getenvW for Windows-specific API.");
     }
     return getenv(mem.sliceTo(key, 0));
 }
diff --git a/lib/std/sort.zig b/lib/std/sort.zig
index 03e9defd35..5edf06e2f7 100644
--- a/lib/std/sort.zig
+++ b/lib/std/sort.zig
@@ -616,7 +616,7 @@ pub fn upperBound(
     var right: usize = items.len;
 
     while (left < right) {
-        const mid = (right + left) / 2;
+        const mid = left + (right - left) / 2;
         if (!lessThan(context, key, items[mid])) {
             left = mid + 1;
         } else {
diff --git a/lib/std/tar.zig b/lib/std/tar.zig
index 9dc5bb4a53..364dc35989 100644
--- a/lib/std/tar.zig
+++ b/lib/std/tar.zig
@@ -29,7 +29,7 @@ pub const Diagnostics = struct {
     allocator: std.mem.Allocator,
     errors: std.ArrayListUnmanaged(Error) = .{},
 
-    root_entries: usize = 0,
+    entries: usize = 0,
     root_dir: []const u8 = "",
 
     pub const Error = union(enum) {
@@ -48,41 +48,40 @@ pub const Diagnostics = struct {
         },
     };
 
-    fn findRoot(d: *Diagnostics, path: []const u8, kind: FileKind) !void {
-        if (rootDir(path)) |root_dir| {
-            d.root_entries += 1;
-            if (kind == .directory and d.root_entries == 1) {
-                d.root_dir = try d.allocator.dupe(u8, root_dir);
-                return;
-            }
-            d.allocator.free(d.root_dir);
-            d.root_dir = "";
+    fn findRoot(d: *Diagnostics, path: []const u8) !void {
+        if (path.len == 0) return;
+
+        d.entries += 1;
+        const root_dir = rootDir(path);
+        if (d.entries == 1) {
+            d.root_dir = try d.allocator.dupe(u8, root_dir);
+            return;
         }
+        if (d.root_dir.len == 0 or std.mem.eql(u8, root_dir, d.root_dir))
+            return;
+        d.allocator.free(d.root_dir);
+        d.root_dir = "";
     }
 
-    // If path is package root returns root_dir name, otherwise null.
-    fn rootDir(path: []const u8) ?[]const u8 {
-        if (path.len == 0) return null;
-
+    // Returns root dir of the path, assumes non empty path.
+    fn rootDir(path: []const u8) []const u8 {
         const start_index: usize = if (path[0] == '/') 1 else 0;
         const end_index: usize = if (path[path.len - 1] == '/') path.len - 1 else path.len;
         const buf = path[start_index..end_index];
-        return if (std.mem.indexOfScalarPos(u8, buf, 0, '/') == null)
-            buf
-        else
-            null;
+        if (std.mem.indexOfScalarPos(u8, buf, 0, '/')) |idx| {
+            return buf[0..idx];
+        }
+        return buf;
     }
 
     test rootDir {
         const expectEqualStrings = testing.expectEqualStrings;
-        const expect = testing.expect;
-
-        try expectEqualStrings("a", rootDir("a").?);
-        try expectEqualStrings("b", rootDir("b").?);
-        try expectEqualStrings("c", rootDir("/c").?);
-        try expectEqualStrings("d", rootDir("/d/").?);
-        try expect(rootDir("a/b") == null);
-        try expect(rootDir("") == null);
+        try expectEqualStrings("a", rootDir("a"));
+        try expectEqualStrings("b", rootDir("b"));
+        try expectEqualStrings("c", rootDir("/c"));
+        try expectEqualStrings("d", rootDir("/d/"));
+        try expectEqualStrings("a", rootDir("a/b"));
+        try expectEqualStrings("a", rootDir("a/b/c"));
     }
 
     pub fn deinit(d: *Diagnostics) void {
@@ -625,7 +624,7 @@ pub fn pipeToFileSystem(dir: std.fs.Dir, reader: anytype, options: PipeOptions)
     while (try iter.next()) |file| {
         const file_name = stripComponents(file.name, options.strip_components);
         if (options.diagnostics) |d| {
-            try d.findRoot(file_name, file.kind);
+            try d.findRoot(file_name);
         }
 
         switch (file.kind) {
@@ -1056,7 +1055,7 @@ test "pipeToFileSystem root_dir" {
 
         // there is no root_dir
         try testing.expectEqual(0, diagnostics.root_dir.len);
-        try testing.expectEqual(3, diagnostics.root_entries);
+        try testing.expectEqual(5, diagnostics.entries);
     }
 
     // with strip_components = 0
@@ -1078,10 +1077,25 @@ test "pipeToFileSystem root_dir" {
 
         // root_dir found
         try testing.expectEqualStrings("example", diagnostics.root_dir);
-        try testing.expectEqual(1, diagnostics.root_entries);
+        try testing.expectEqual(6, diagnostics.entries);
     }
 }
 
+test "findRoot without explicit root dir" {
+    const data = @embedFile("tar/testdata/19820.tar");
+    var fbs = std.io.fixedBufferStream(data);
+    const reader = fbs.reader();
+
+    var tmp = testing.tmpDir(.{});
+    defer tmp.cleanup();
+
+    var diagnostics: Diagnostics = .{ .allocator = testing.allocator };
+    defer diagnostics.deinit();
+    try pipeToFileSystem(tmp.dir, reader, .{ .diagnostics = &diagnostics });
+
+    try testing.expectEqualStrings("root", diagnostics.root_dir);
+}
+
 fn normalizePath(bytes: []u8) []u8 {
     const canonical_sep = std.fs.path.sep_posix;
     if (std.fs.path.sep == canonical_sep) return bytes;
diff --git a/lib/std/tar/testdata/19820.tar b/lib/std/tar/testdata/19820.tar
new file mode 100644
index 0000000000..6ded61f6b7
Binary files /dev/null and b/lib/std/tar/testdata/19820.tar differ
diff --git a/lib/std/unicode.zig b/lib/std/unicode.zig
index 9d1f52fb2d..327c485fd7 100644
--- a/lib/std/unicode.zig
+++ b/lib/std/unicode.zig
@@ -934,7 +934,7 @@ fn utf16LeToUtf8ArrayListImpl(
     .cannot_encode_surrogate_half => Utf16LeToUtf8AllocError,
     .can_encode_surrogate_half => mem.Allocator.Error,
 })!void {
-    assert(result.capacity >= utf16le.len);
+    assert(result.unusedCapacitySlice().len >= utf16le.len);
 
     var remaining = utf16le;
     vectorized: {
@@ -979,7 +979,7 @@ fn utf16LeToUtf8ArrayListImpl(
 pub const Utf16LeToUtf8AllocError = mem.Allocator.Error || Utf16LeToUtf8Error;
 
 pub fn utf16LeToUtf8ArrayList(result: *std.ArrayList(u8), utf16le: []const u16) Utf16LeToUtf8AllocError!void {
-    try result.ensureTotalCapacityPrecise(utf16le.len);
+    try result.ensureUnusedCapacity(utf16le.len);
     return utf16LeToUtf8ArrayListImpl(result, utf16le, .cannot_encode_surrogate_half);
 }
 
@@ -1138,7 +1138,7 @@ test utf16LeToUtf8 {
 }
 
 fn utf8ToUtf16LeArrayListImpl(result: *std.ArrayList(u16), utf8: []const u8, comptime surrogates: Surrogates) !void {
-    assert(result.capacity >= utf8.len);
+    assert(result.unusedCapacitySlice().len >= utf8.len);
 
     var remaining = utf8;
     vectorized: {
@@ -1176,7 +1176,7 @@ fn utf8ToUtf16LeArrayListImpl(result: *std.ArrayList(u16), utf8: []const u8, com
 }
 
 pub fn utf8ToUtf16LeArrayList(result: *std.ArrayList(u16), utf8: []const u8) error{ InvalidUtf8, OutOfMemory }!void {
-    try result.ensureTotalCapacityPrecise(utf8.len);
+    try result.ensureUnusedCapacity(utf8.len);
     return utf8ToUtf16LeArrayListImpl(result, utf8, .cannot_encode_surrogate_half);
 }
 
@@ -1351,6 +1351,64 @@ test utf8ToUtf16LeAllocZ {
     }
 }
 
+test "ArrayList functions on a re-used list" {
+    // utf8ToUtf16LeArrayList
+    {
+        var list = std.ArrayList(u16).init(testing.allocator);
+        defer list.deinit();
+
+        const init_slice = utf8ToUtf16LeStringLiteral("abcdefg");
+        try list.ensureTotalCapacityPrecise(init_slice.len);
+        list.appendSliceAssumeCapacity(init_slice);
+
+        try utf8ToUtf16LeArrayList(&list, "hijklmnopqrstuvwyxz");
+
+        try testing.expectEqualSlices(u16, utf8ToUtf16LeStringLiteral("abcdefghijklmnopqrstuvwyxz"), list.items);
+    }
+
+    // utf16LeToUtf8ArrayList
+    {
+        var list = std.ArrayList(u8).init(testing.allocator);
+        defer list.deinit();
+
+        const init_slice = "abcdefg";
+        try list.ensureTotalCapacityPrecise(init_slice.len);
+        list.appendSliceAssumeCapacity(init_slice);
+
+        try utf16LeToUtf8ArrayList(&list, utf8ToUtf16LeStringLiteral("hijklmnopqrstuvwyxz"));
+
+        try testing.expectEqualStrings("abcdefghijklmnopqrstuvwyxz", list.items);
+    }
+
+    // wtf8ToWtf16LeArrayList
+    {
+        var list = std.ArrayList(u16).init(testing.allocator);
+        defer list.deinit();
+
+        const init_slice = utf8ToUtf16LeStringLiteral("abcdefg");
+        try list.ensureTotalCapacityPrecise(init_slice.len);
+        list.appendSliceAssumeCapacity(init_slice);
+
+        try wtf8ToWtf16LeArrayList(&list, "hijklmnopqrstuvwyxz");
+
+        try testing.expectEqualSlices(u16, utf8ToUtf16LeStringLiteral("abcdefghijklmnopqrstuvwyxz"), list.items);
+    }
+
+    // wtf16LeToWtf8ArrayList
+    {
+        var list = std.ArrayList(u8).init(testing.allocator);
+        defer list.deinit();
+
+        const init_slice = "abcdefg";
+        try list.ensureTotalCapacityPrecise(init_slice.len);
+        list.appendSliceAssumeCapacity(init_slice);
+
+        try wtf16LeToWtf8ArrayList(&list, utf8ToUtf16LeStringLiteral("hijklmnopqrstuvwyxz"));
+
+        try testing.expectEqualStrings("abcdefghijklmnopqrstuvwyxz", list.items);
+    }
+}
+
 /// Converts a UTF-8 string literal into a UTF-16LE string literal.
 pub fn utf8ToUtf16LeStringLiteral(comptime utf8: []const u8) *const [calcUtf16LeLen(utf8) catch |err| @compileError(err):0]u16 {
     return comptime blk: {
@@ -1685,7 +1743,7 @@ pub const Wtf8Iterator = struct {
 };
 
 pub fn wtf16LeToWtf8ArrayList(result: *std.ArrayList(u8), utf16le: []const u16) mem.Allocator.Error!void {
-    try result.ensureTotalCapacityPrecise(utf16le.len);
+    try result.ensureUnusedCapacity(utf16le.len);
     return utf16LeToUtf8ArrayListImpl(result, utf16le, .can_encode_surrogate_half);
 }
 
@@ -1714,7 +1772,7 @@ pub fn wtf16LeToWtf8(wtf8: []u8, wtf16le: []const u16) usize {
 }
 
 pub fn wtf8ToWtf16LeArrayList(result: *std.ArrayList(u16), wtf8: []const u8) error{ InvalidWtf8, OutOfMemory }!void {
-    try result.ensureTotalCapacityPrecise(wtf8.len);
+    try result.ensureUnusedCapacity(wtf8.len);
     return utf8ToUtf16LeArrayListImpl(result, wtf8, .can_encode_surrogate_half);
 }
 
diff --git a/lib/std/zig/AstGen.zig b/lib/std/zig/AstGen.zig
index a52007eabf..45a6e0fcb2 100644
--- a/lib/std/zig/AstGen.zig
+++ b/lib/std/zig/AstGen.zig
@@ -7071,8 +7071,10 @@ fn switchExprErrUnion(
         .ctx = ri.ctx,
     };
 
-    const payload_is_ref = node_ty == .@"if" and
-        if_full.payload_token != null and token_tags[if_full.payload_token.?] == .asterisk;
+    const payload_is_ref = switch (node_ty) {
+        .@"if" => if_full.payload_token != null and token_tags[if_full.payload_token.?] == .asterisk,
+        .@"catch" => ri.rl == .ref or ri.rl == .ref_coerced_ty,
+    };
 
     // We need to call `rvalue` to write through to the pointer only if we had a
     // result pointer and aren't forwarding it.
@@ -9459,7 +9461,7 @@ fn builtinCall(
         },
         .wasm_memory_grow => {
             const index_arg = try comptimeExpr(gz, scope, .{ .rl = .{ .coerced_ty = .u32_type } }, params[0]);
-            const delta_arg = try expr(gz, scope, .{ .rl = .{ .coerced_ty = .u32_type } }, params[1]);
+            const delta_arg = try expr(gz, scope, .{ .rl = .{ .coerced_ty = .usize_type } }, params[1]);
             const result = try gz.addExtendedPayload(.wasm_memory_grow, Zir.Inst.BinNode{
                 .node = gz.nodeIndexToRelative(node),
                 .lhs = index_arg,
diff --git a/lib/std/zig/WindowsSdk.zig b/lib/std/zig/WindowsSdk.zig
index bebb0fc5a1..01a2e7d263 100644
--- a/lib/std/zig/WindowsSdk.zig
+++ b/lib/std/zig/WindowsSdk.zig
@@ -23,7 +23,7 @@ pub fn find(allocator: std.mem.Allocator) error{ OutOfMemory, NotFound, PathTooL
     if (builtin.os.tag != .windows) return error.NotFound;
 
     //note(dimenus): If this key doesn't exist, neither the Win 8 SDK nor the Win 10 SDK is installed
-    const roots_key = RegistryWtf8.openKey(windows.HKEY_LOCAL_MACHINE, windows_kits_reg_key) catch |err| switch (err) {
+    const roots_key = RegistryWtf8.openKey(windows.HKEY_LOCAL_MACHINE, windows_kits_reg_key, .{ .wow64_32 = true }) catch |err| switch (err) {
         error.KeyNotFound => return error.NotFound,
     };
     defer roots_key.closeKey();
@@ -137,11 +137,17 @@ fn iterateAndFilterByVersion(
     return dirs.toOwnedSlice();
 }
 
+const OpenOptions = struct {
+    /// Sets the KEY_WOW64_32KEY access flag.
+    /// https://learn.microsoft.com/en-us/windows/win32/winprog64/accessing-an-alternate-registry-view
+    wow64_32: bool = false,
+};
+
 const RegistryWtf8 = struct {
     key: windows.HKEY,
 
     /// Assert that `key` is valid WTF-8 string
-    pub fn openKey(hkey: windows.HKEY, key: []const u8) error{KeyNotFound}!RegistryWtf8 {
+    pub fn openKey(hkey: windows.HKEY, key: []const u8, options: OpenOptions) error{KeyNotFound}!RegistryWtf8 {
         const key_wtf16le: [:0]const u16 = key_wtf16le: {
             var key_wtf16le_buf: [RegistryWtf16Le.key_name_max_len]u16 = undefined;
             const key_wtf16le_len: usize = std.unicode.wtf8ToWtf16Le(key_wtf16le_buf[0..], key) catch |err| switch (err) {
@@ -151,7 +157,7 @@ const RegistryWtf8 = struct {
             break :key_wtf16le key_wtf16le_buf[0..key_wtf16le_len :0];
         };
 
-        const registry_wtf16le = try RegistryWtf16Le.openKey(hkey, key_wtf16le);
+        const registry_wtf16le = try RegistryWtf16Le.openKey(hkey, key_wtf16le, options);
         return .{ .key = registry_wtf16le.key };
     }
 
@@ -239,15 +245,17 @@ const RegistryWtf16Le = struct {
     pub const value_name_max_len = 16_383;
 
     /// Under HKEY_LOCAL_MACHINE with flags:
-    /// KEY_QUERY_VALUE, KEY_WOW64_32KEY, and KEY_ENUMERATE_SUB_KEYS.
+    /// KEY_QUERY_VALUE, KEY_ENUMERATE_SUB_KEYS, optionally KEY_WOW64_32KEY.
     /// After finishing work, call `closeKey`.
-    fn openKey(hkey: windows.HKEY, key_wtf16le: [:0]const u16) error{KeyNotFound}!RegistryWtf16Le {
+    fn openKey(hkey: windows.HKEY, key_wtf16le: [:0]const u16, options: OpenOptions) error{KeyNotFound}!RegistryWtf16Le {
         var key: windows.HKEY = undefined;
+        var access: windows.REGSAM = windows.KEY_QUERY_VALUE | windows.KEY_ENUMERATE_SUB_KEYS;
+        if (options.wow64_32) access |= windows.KEY_WOW64_32KEY;
         const return_code_int: windows.HRESULT = windows.advapi32.RegOpenKeyExW(
             hkey,
             key_wtf16le,
             0,
-            windows.KEY_QUERY_VALUE | windows.KEY_WOW64_32KEY | windows.KEY_ENUMERATE_SUB_KEYS,
+            access,
             &key,
         );
         const return_code: windows.Win32Error = @enumFromInt(return_code_int);
@@ -484,13 +492,14 @@ pub const Installation = struct {
         version_key_name: []const u8,
     ) error{ OutOfMemory, InstallationNotFound, PathTooLong, VersionTooLong }!Installation {
         var key_name_buf: [RegistryWtf16Le.key_name_max_len]u8 = undefined;
-        const key = key: for ([_][]const u8{ "\\Wow6432Node", "" }) |wow6432node| {
+        const key_name = std.fmt.bufPrint(
+            &key_name_buf,
+            "SOFTWARE\\Microsoft\\Microsoft SDKs\\Windows\\{s}",
+            .{version_key_name},
+        ) catch unreachable;
+        const key = key: for ([_]bool{ true, false }) |wow6432node| {
             for ([_]windows.HKEY{ windows.HKEY_LOCAL_MACHINE, windows.HKEY_CURRENT_USER }) |hkey| {
-                break :key RegistryWtf8.openKey(hkey, std.fmt.bufPrint(
-                    &key_name_buf,
-                    "SOFTWARE{s}\\Microsoft\\Microsoft SDKs\\Windows\\{s}",
-                    .{ wow6432node, version_key_name },
-                ) catch unreachable) catch |err| switch (err) {
+                break :key RegistryWtf8.openKey(hkey, key_name, .{ .wow64_32 = wow6432node }) catch |err| switch (err) {
                     error.KeyNotFound => return error.InstallationNotFound,
                 };
             }
@@ -563,6 +572,7 @@ pub const Installation = struct {
         const options_key = RegistryWtf8.openKey(
             windows.HKEY_LOCAL_MACHINE,
             reg_query_as_wtf8,
+            .{ .wow64_32 = true },
         ) catch |err| switch (err) {
             error.KeyNotFound => return false,
         };
@@ -587,9 +597,34 @@ pub const Installation = struct {
 };
 
 const MsvcLibDir = struct {
+    fn findInstancesDirViaSetup(allocator: std.mem.Allocator) error{ OutOfMemory, PathNotFound }!std.fs.Dir {
+        const vs_setup_key_path = "SOFTWARE\\Microsoft\\VisualStudio\\Setup";
+        const vs_setup_key = RegistryWtf8.openKey(windows.HKEY_LOCAL_MACHINE, vs_setup_key_path, .{}) catch |err| switch (err) {
+            error.KeyNotFound => return error.PathNotFound,
+        };
+        defer vs_setup_key.closeKey();
+
+        const packages_path = vs_setup_key.getString(allocator, "", "CachePath") catch |err| switch (err) {
+            error.NotAString,
+            error.ValueNameNotFound,
+            error.StringNotFound,
+            => return error.PathNotFound,
+
+            error.OutOfMemory => return error.OutOfMemory,
+        };
+        defer allocator.free(packages_path);
+
+        if (!std.fs.path.isAbsolute(packages_path)) return error.PathNotFound;
+
+        const instances_path = try std.fs.path.join(allocator, &.{ packages_path, "_Instances" });
+        defer allocator.free(instances_path);
+
+        return std.fs.openDirAbsolute(instances_path, .{ .iterate = true }) catch return error.PathNotFound;
+    }
+
     fn findInstancesDirViaCLSID(allocator: std.mem.Allocator) error{ OutOfMemory, PathNotFound }!std.fs.Dir {
         const setup_configuration_clsid = "{177f0c4a-1cd3-4de7-a32c-71dbbb9fa36d}";
-        const setup_config_key = RegistryWtf8.openKey(windows.HKEY_CLASSES_ROOT, "CLSID\\" ++ setup_configuration_clsid) catch |err| switch (err) {
+        const setup_config_key = RegistryWtf8.openKey(windows.HKEY_CLASSES_ROOT, "CLSID\\" ++ setup_configuration_clsid, .{}) catch |err| switch (err) {
             error.KeyNotFound => return error.PathNotFound,
         };
         defer setup_config_key.closeKey();
@@ -604,6 +639,8 @@ const MsvcLibDir = struct {
         };
         defer allocator.free(dll_path);
 
+        if (!std.fs.path.isAbsolute(dll_path)) return error.PathNotFound;
+
         var path_it = std.fs.path.componentIterator(dll_path) catch return error.PathNotFound;
         // the .dll filename
         _ = path_it.last();
@@ -622,22 +659,40 @@ const MsvcLibDir = struct {
     }
 
     fn findInstancesDir(allocator: std.mem.Allocator) error{ OutOfMemory, PathNotFound }!std.fs.Dir {
-        // First try to get the path from the .dll that would have been
+        // First, try getting the packages cache path from the registry.
+        // This only seems to exist when the path is different from the default.
+        method1: {
+            return findInstancesDirViaSetup(allocator) catch |err| switch (err) {
+                error.OutOfMemory => |e| return e,
+                error.PathNotFound => break :method1,
+            };
+        }
+        // Otherwise, try to get the path from the .dll that would have been
         // loaded via COM for SetupConfiguration.
-        return findInstancesDirViaCLSID(allocator) catch |orig_err| {
-            // If that can't be found, fall back to manually appending
-            // `Microsoft\VisualStudio\Packages\_Instances` to %PROGRAMDATA%
+        method2: {
+            return findInstancesDirViaCLSID(allocator) catch |err| switch (err) {
+                error.OutOfMemory => |e| return e,
+                error.PathNotFound => break :method2,
+            };
+        }
+        // If that can't be found, fall back to manually appending
+        // `Microsoft\VisualStudio\Packages\_Instances` to %PROGRAMDATA%
+        method3: {
             const program_data = std.process.getEnvVarOwned(allocator, "PROGRAMDATA") catch |err| switch (err) {
                 error.OutOfMemory => |e| return e,
-                else => return orig_err,
+                error.InvalidWtf8 => unreachable,
+                error.EnvironmentVariableNotFound => break :method3,
             };
             defer allocator.free(program_data);
 
+            if (!std.fs.path.isAbsolute(program_data)) break :method3;
+
             const instances_path = try std.fs.path.join(allocator, &.{ program_data, "Microsoft", "VisualStudio", "Packages", "_Instances" });
             defer allocator.free(instances_path);
 
-            return std.fs.openDirAbsolute(instances_path, .{ .iterate = true }) catch return orig_err;
-        };
+            return std.fs.openDirAbsolute(instances_path, .{ .iterate = true }) catch break :method3;
+        }
+        return error.PathNotFound;
     }
 
     /// Intended to be equivalent to `ISetupHelper.ParseVersion`
@@ -896,7 +951,7 @@ const MsvcLibDir = struct {
                 }
             }
 
-            const vs7_key = RegistryWtf8.openKey(windows.HKEY_LOCAL_MACHINE, "SOFTWARE\\Microsoft\\VisualStudio\\SxS\\VS7") catch return error.PathNotFound;
+            const vs7_key = RegistryWtf8.openKey(windows.HKEY_LOCAL_MACHINE, "SOFTWARE\\Microsoft\\VisualStudio\\SxS\\VS7", .{ .wow64_32 = true }) catch return error.PathNotFound;
             defer vs7_key.closeKey();
             try_vs7_key: {
                 const path_maybe_with_trailing_slash = vs7_key.getString(allocator, "", "14.0") catch |err| switch (err) {
diff --git a/lib/std/zig/Zir.zig b/lib/std/zig/Zir.zig
index 64e8a1c805..9453790fcf 100644
--- a/lib/std/zig/Zir.zig
+++ b/lib/std/zig/Zir.zig
@@ -2194,9 +2194,6 @@ pub const Inst = struct {
         empty_struct,
         generic_poison,
 
-        /// This tag is here to match Air and InternPool, however it is unused
-        /// for ZIR purposes.
-        var_args_param_type = std.math.maxInt(u32) - 1,
         /// This Ref does not correspond to any ZIR instruction or constant
         /// value and may instead be used as a sentinel to indicate null.
         none = std.math.maxInt(u32),
diff --git a/lib/std/zig/system.zig b/lib/std/zig/system.zig
index 8bd7f815fe..83c798c342 100644
--- a/lib/std/zig/system.zig
+++ b/lib/std/zig/system.zig
@@ -983,7 +983,7 @@ fn detectAbiAndDynamicLinker(
 
     // Best case scenario: the executable is dynamically linked, and we can iterate
     // over our own shared objects and find a dynamic linker.
-    const elf_file = blk: {
+    const elf_file = elf_file: {
         // This block looks for a shebang line in /usr/bin/env,
         // if it finds one, then instead of using /usr/bin/env as the ELF file to examine, it uses the file it references instead,
         // doing the same logic recursively in case it finds another shebang line.
@@ -995,9 +995,22 @@ fn detectAbiAndDynamicLinker(
             // Haiku does not have a /usr root directory.
             .haiku => "/bin/env",
         };
-        // #! (2) + 255 (max length of shebang line since Linux 5.1) + \n (1)
-        var buffer: [258]u8 = undefined;
+
+        // According to `man 2 execve`:
+        //
+        // The kernel imposes a maximum length on the text
+        // that follows the "#!" characters at the start of a script;
+        // characters beyond the limit are ignored.
+        // Before Linux 5.1, the limit is 127 characters.
+        // Since Linux 5.1, the limit is 255 characters.
+        //
+        // Tests show that bash and zsh consider 255 as total limit,
+        // *including* "#!" characters and ignoring newline.
+        // For safety, we set max length as 255 + \n (1).
+        var buffer: [255 + 1]u8 = undefined;
         while (true) {
+            // Interpreter path can be relative on Linux, but
+            // for simplicity we are asserting it is an absolute path.
             const file = fs.openFileAbsolute(file_name, .{}) catch |err| switch (err) {
                 error.NoSpaceLeft => unreachable,
                 error.NameTooLong => unreachable,
@@ -1027,27 +1040,55 @@ fn detectAbiAndDynamicLinker(
 
                 else => |e| return e,
             };
-            errdefer file.close();
+            var is_elf_file = false;
+            defer if (is_elf_file == false) file.close();
 
-            const len = preadAtLeast(file, &buffer, 0, buffer.len) catch |err| switch (err) {
+            // Shortest working interpreter path is "#!/i" (4)
+            // (interpreter is "/i", assuming all pathes are absolute, like in above comment).
+            // ELF magic number length is also 4.
+            //
+            // If file is shorter than that, it is definitely not ELF file
+            // nor file with "shebang" line.
+            const min_len: usize = 4;
+
+            const len = preadAtLeast(file, &buffer, 0, min_len) catch |err| switch (err) {
                 error.UnexpectedEndOfFile,
                 error.UnableToReadElfFile,
-                => break :blk file,
+                => return defaultAbiAndDynamicLinker(cpu, os, query),
 
                 else => |e| return e,
             };
-            const newline = mem.indexOfScalar(u8, buffer[0..len], '\n') orelse break :blk file;
-            const line = buffer[0..newline];
-            if (!mem.startsWith(u8, line, "#!")) break :blk file;
-            var it = mem.tokenizeScalar(u8, line[2..], ' ');
-            file_name = it.next() orelse return defaultAbiAndDynamicLinker(cpu, os, query);
-            file.close();
+            const content = buffer[0..len];
+
+            if (mem.eql(u8, content[0..4], std.elf.MAGIC)) {
+                // It is very likely ELF file!
+                is_elf_file = true;
+                break :elf_file file;
+            } else if (mem.eql(u8, content[0..2], "#!")) {
+                // We detected shebang, now parse entire line.
+
+                // Trim leading "#!", spaces and tabs.
+                const trimmed_line = mem.trimLeft(u8, content[2..], &.{ ' ', '\t' });
+
+                // This line can have:
+                // * Interpreter path only,
+                // * Interpreter path and arguments, all separated by space, tab or NUL character.
+                // And optionally newline at the end.
+                const path_maybe_args = mem.trimRight(u8, trimmed_line, "\n");
+
+                // Separate path and args.
+                const path_end = mem.indexOfAny(u8, path_maybe_args, &.{ ' ', '\t', 0 }) orelse path_maybe_args.len;
+
+                file_name = path_maybe_args[0..path_end];
+                continue;
+            } else {
+                // Not a ELF file, not a shell script with "shebang line", invalid duck.
+                return defaultAbiAndDynamicLinker(cpu, os, query);
+            }
         }
     };
     defer elf_file.close();
 
-    // If Zig is statically linked, such as via distributed binary static builds, the above
-    // trick (block self_exe) won't work. The next thing we fall back to is the same thing, but for elf_file.
     // TODO: inline this function and combine the buffer we already read above to find
     // the possible shebang line with the buffer we use for the ELF header.
     return abiAndDynamicLinkerFromFile(elf_file, cpu, os, ld_info_list, query) catch |err| switch (err) {
@@ -1075,7 +1116,7 @@ fn detectAbiAndDynamicLinker(
     };
 }
 
-fn defaultAbiAndDynamicLinker(cpu: Target.Cpu, os: Target.Os, query: Target.Query) !Target {
+fn defaultAbiAndDynamicLinker(cpu: Target.Cpu, os: Target.Os, query: Target.Query) Target {
     const abi = query.abi orelse Target.Abi.default(cpu.arch, os);
     return .{
         .cpu = cpu,
diff --git a/lib/zig.h b/lib/zig.h
index ec7508670d..1e9da15a3f 100644
--- a/lib/zig.h
+++ b/lib/zig.h
@@ -530,6 +530,10 @@ typedef ptrdiff_t intptr_t;
         return (val & UINT##w##_C(1) << (bits - UINT8_C(1))) != 0 \
             ? val | zig_minInt_i(w, bits) : val & zig_maxInt_i(w, bits); \
     } \
+\
+    static inline uint##w##_t zig_abs_i##w(int##w##_t val) { \
+        return (val < 0) ? -(uint##w##_t)val : (uint##w##_t)val; \
+    } \
 \
     zig_basic_operator(uint##w##_t, div_floor_u##w, /) \
 \
@@ -990,24 +994,6 @@ typedef unsigned long zig_Builtin64;
 typedef unsigned long long zig_Builtin64;
 #endif
 
-#define zig_builtin8_rev(name, val) __builtin_##name(val)
-
-#define zig_builtin16_rev(name, val) __builtin_##name(val)
-
-#if INT_MIN <= INT32_MIN
-#define zig_builtin32_rev(name, val) __builtin_##name(val)
-#elif LONG_MIN <= INT32_MIN
-#define zig_builtin32_rev(name, val) __builtin_l##name(val)
-#endif
-
-#if INT_MIN <= INT64_MIN
-#define zig_builtin64_rev(name, val) __builtin_##name(val)
-#elif LONG_MIN <= INT64_MIN
-#define zig_builtin64_rev(name, val) __builtin_l##name(val)
-#elif LLONG_MIN <= INT64_MIN
-#define zig_builtin64_rev(name, val) __builtin_ll##name(val)
-#endif
-
 static inline uint8_t zig_byte_swap_u8(uint8_t val, uint8_t bits) {
     return zig_wrap_u8(val >> (8 - bits), bits);
 }
@@ -1203,24 +1189,6 @@ zig_builtin_clz(16)
 zig_builtin_clz(32)
 zig_builtin_clz(64)
 
-#if zig_has_builtin(abs) || defined(zig_gnuc)
-#define zig_builtin_abs(w) \
-    static inline int##w##_t zig_abs_i##w(int##w##_t val) { \
-        return zig_builtin##w##_rev(abs, val); \
-    }
-#else
-#define zig_builtin_abs(w) \
-    static inline int##w##_t zig_abs_i##w(int##w##_t val) { \
-        if (val == INT##w##_MIN) return val; \
-        int##w##_t tmp = val >> (w - 1); \
-        return (val ^ tmp) - tmp; \
-    }
-#endif
-zig_builtin_abs(8)
-zig_builtin_abs(16)
-zig_builtin_abs(32)
-zig_builtin_abs(64)
-
 /* ======================== 128-bit Integer Support ========================= */
 
 #if !defined(zig_has_int128)
@@ -3375,31 +3343,31 @@ zig_float_negate_builtin(128, zig_make_u128, (UINT64_C(1) << 63, UINT64_C(0)))
     zig_expand_concat(zig_float_binary_builtin_,  zig_has_f##w)(f##w, sub, -) \
     zig_expand_concat(zig_float_binary_builtin_,  zig_has_f##w)(f##w, mul, *) \
     zig_expand_concat(zig_float_binary_builtin_,  zig_has_f##w)(f##w, div, /) \
-    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(sqrt)))(zig_f##w, zig_float_fn_f##w##_sqrt, zig_libc_name_f##w(sqrt), (zig_f##w x), (x)) \
-    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(sin)))(zig_f##w, zig_float_fn_f##w##_sin, zig_libc_name_f##w(sin), (zig_f##w x), (x)) \
-    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(cos)))(zig_f##w, zig_float_fn_f##w##_cos, zig_libc_name_f##w(cos), (zig_f##w x), (x)) \
-    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(tan)))(zig_f##w, zig_float_fn_f##w##_tan, zig_libc_name_f##w(tan), (zig_f##w x), (x)) \
-    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(exp)))(zig_f##w, zig_float_fn_f##w##_exp, zig_libc_name_f##w(exp), (zig_f##w x), (x)) \
-    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(exp2)))(zig_f##w, zig_float_fn_f##w##_exp2, zig_libc_name_f##w(exp2), (zig_f##w x), (x)) \
-    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(log)))(zig_f##w, zig_float_fn_f##w##_log, zig_libc_name_f##w(log), (zig_f##w x), (x)) \
-    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(log2)))(zig_f##w, zig_float_fn_f##w##_log2, zig_libc_name_f##w(log2), (zig_f##w x), (x)) \
-    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(log10)))(zig_f##w, zig_float_fn_f##w##_log10, zig_libc_name_f##w(log10), (zig_f##w x), (x)) \
-    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(fabs)))(zig_f##w, zig_float_fn_f##w##_fabs, zig_libc_name_f##w(fabs), (zig_f##w x), (x)) \
-    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(floor)))(zig_f##w, zig_float_fn_f##w##_floor, zig_libc_name_f##w(floor), (zig_f##w x), (x)) \
-    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(ceil)))(zig_f##w, zig_float_fn_f##w##_ceil, zig_libc_name_f##w(ceil), (zig_f##w x), (x)) \
-    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(round)))(zig_f##w, zig_float_fn_f##w##_round, zig_libc_name_f##w(round), (zig_f##w x), (x)) \
-    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(trunc)))(zig_f##w, zig_float_fn_f##w##_trunc, zig_libc_name_f##w(trunc), (zig_f##w x), (x)) \
-    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(fmod)))(zig_f##w, zig_float_fn_f##w##_fmod, zig_libc_name_f##w(fmod), (zig_f##w x, zig_f##w y), (x, y)) \
-    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(fmin)))(zig_f##w, zig_float_fn_f##w##_fmin, zig_libc_name_f##w(fmin), (zig_f##w x, zig_f##w y), (x, y)) \
-    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(fmax)))(zig_f##w, zig_float_fn_f##w##_fmax, zig_libc_name_f##w(fmax), (zig_f##w x, zig_f##w y), (x, y)) \
-    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(fma)))(zig_f##w, zig_float_fn_f##w##_fma, zig_libc_name_f##w(fma), (zig_f##w x, zig_f##w y, zig_f##w z), (x, y, z)) \
+    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(sqrt)))(zig_f##w, zig_sqrt_f##w, zig_libc_name_f##w(sqrt), (zig_f##w x), (x)) \
+    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(sin)))(zig_f##w, zig_sin_f##w, zig_libc_name_f##w(sin), (zig_f##w x), (x)) \
+    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(cos)))(zig_f##w, zig_cos_f##w, zig_libc_name_f##w(cos), (zig_f##w x), (x)) \
+    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(tan)))(zig_f##w, zig_tan_f##w, zig_libc_name_f##w(tan), (zig_f##w x), (x)) \
+    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(exp)))(zig_f##w, zig_exp_f##w, zig_libc_name_f##w(exp), (zig_f##w x), (x)) \
+    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(exp2)))(zig_f##w, zig_exp2_f##w, zig_libc_name_f##w(exp2), (zig_f##w x), (x)) \
+    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(log)))(zig_f##w, zig_log_f##w, zig_libc_name_f##w(log), (zig_f##w x), (x)) \
+    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(log2)))(zig_f##w, zig_log2_f##w, zig_libc_name_f##w(log2), (zig_f##w x), (x)) \
+    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(log10)))(zig_f##w, zig_log10_f##w, zig_libc_name_f##w(log10), (zig_f##w x), (x)) \
+    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(fabs)))(zig_f##w, zig_abs_f##w, zig_libc_name_f##w(fabs), (zig_f##w x), (x)) \
+    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(floor)))(zig_f##w, zig_floor_f##w, zig_libc_name_f##w(floor), (zig_f##w x), (x)) \
+    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(ceil)))(zig_f##w, zig_ceil_f##w, zig_libc_name_f##w(ceil), (zig_f##w x), (x)) \
+    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(round)))(zig_f##w, zig_round_f##w, zig_libc_name_f##w(round), (zig_f##w x), (x)) \
+    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(trunc)))(zig_f##w, zig_trunc_f##w, zig_libc_name_f##w(trunc), (zig_f##w x), (x)) \
+    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(fmod)))(zig_f##w, zig_fmod_f##w, zig_libc_name_f##w(fmod), (zig_f##w x, zig_f##w y), (x, y)) \
+    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(fmin)))(zig_f##w, zig_min_f##w, zig_libc_name_f##w(fmin), (zig_f##w x, zig_f##w y), (x, y)) \
+    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(fmax)))(zig_f##w, zig_max_f##w, zig_libc_name_f##w(fmax), (zig_f##w x, zig_f##w y), (x, y)) \
+    zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(fma)))(zig_f##w, zig_fma_f##w, zig_libc_name_f##w(fma), (zig_f##w x, zig_f##w y, zig_f##w z), (x, y, z)) \
 \
     static inline zig_f##w zig_div_trunc_f##w(zig_f##w lhs, zig_f##w rhs) { \
-        return zig_float_fn_f##w##_trunc(zig_div_f##w(lhs, rhs)); \
+        return zig_trunc_f##w(zig_div_f##w(lhs, rhs)); \
     } \
 \
     static inline zig_f##w zig_div_floor_f##w(zig_f##w lhs, zig_f##w rhs) { \
-        return zig_float_fn_f##w##_floor(zig_div_f##w(lhs, rhs)); \
+        return zig_floor_f##w(zig_div_f##w(lhs, rhs)); \
     } \
 \
     static inline zig_f##w zig_mod_f##w(zig_f##w lhs, zig_f##w rhs) { \
@@ -3503,7 +3471,7 @@ zig_float_builtins(64)
     zig_##Type zig_atomicrmw_desired; \
     zig_atomic_load(zig_atomicrmw_expected, obj, zig_memory_order_relaxed, Type, ReprType); \
     do { \
-        zig_atomicrmw_desired = zig_float_fn_##Type##_fmin(zig_atomicrmw_expected, arg); \
+        zig_atomicrmw_desired = zig_min_##Type(zig_atomicrmw_expected, arg); \
     } while (!zig_cmpxchg_weak(obj, zig_atomicrmw_expected, zig_atomicrmw_desired, order, zig_memory_order_relaxed, Type, ReprType)); \
     res = zig_atomicrmw_expected; \
 } while (0)
@@ -3512,7 +3480,7 @@ zig_float_builtins(64)
     zig_##Type zig_atomicrmw_desired; \
     zig_atomic_load(zig_atomicrmw_expected, obj, zig_memory_order_relaxed, Type, ReprType); \
     do { \
-        zig_atomicrmw_desired = zig_float_fn_##Type##_fmax(zig_atomicrmw_expected, arg); \
+        zig_atomicrmw_desired = zig_max_##Type(zig_atomicrmw_expected, arg); \
     } while (!zig_cmpxchg_weak(obj, zig_atomicrmw_expected, zig_atomicrmw_desired, order, zig_memory_order_relaxed, Type, ReprType)); \
     res = zig_atomicrmw_expected; \
 } while (0)
diff --git a/src/Air.zig b/src/Air.zig
index 9554c55561..9d7016155e 100644
--- a/src/Air.zig
+++ b/src/Air.zig
@@ -782,13 +782,13 @@ pub const Inst = struct {
         field_parent_ptr,
 
         /// Implements @wasmMemorySize builtin.
-        /// Result type is always `u32`,
+        /// Result type is always `usize`,
         /// Uses the `pl_op` field, payload represents the index of the target memory.
         /// The operand is unused and always set to `Ref.none`.
         wasm_memory_size,
 
         /// Implements @wasmMemoryGrow builtin.
-        /// Result type is always `i32`,
+        /// Result type is always `isize`,
         /// Uses the `pl_op` field, payload represents the index of the target memory.
         wasm_memory_grow,
 
@@ -891,8 +891,7 @@ pub const Inst = struct {
     /// The most-significant bit of the value is a tag bit. This bit is 1 if the value represents an
     /// instruction index and 0 if it represents an InternPool index.
     ///
-    /// The hardcoded refs `none` and `var_args_param_type` are exceptions to this rule: they have
-    /// their tag bit set but refer to the InternPool.
+    /// The ref `none` is an exception: it has the tag bit set but refers to the InternPool.
     pub const Ref = enum(u32) {
         u0_type = @intFromEnum(InternPool.Index.u0_type),
         i0_type = @intFromEnum(InternPool.Index.i0_type),
@@ -979,9 +978,6 @@ pub const Inst = struct {
         empty_struct = @intFromEnum(InternPool.Index.empty_struct),
         generic_poison = @intFromEnum(InternPool.Index.generic_poison),
 
-        /// This Ref does not correspond to any AIR instruction or constant
-        /// value. It is used to handle argument types of var args functions.
-        var_args_param_type = @intFromEnum(InternPool.Index.var_args_param_type),
         /// This Ref does not correspond to any AIR instruction or constant
         /// value and may instead be used as a sentinel to indicate null.
         none = @intFromEnum(InternPool.Index.none),
@@ -994,7 +990,6 @@ pub const Inst = struct {
 
         pub fn toInternedAllowNone(ref: Ref) ?InternPool.Index {
             return switch (ref) {
-                .var_args_param_type => .var_args_param_type,
                 .none => .none,
                 else => if (@intFromEnum(ref) >> 31 == 0)
                     @enumFromInt(@as(u31, @truncate(@intFromEnum(ref))))
@@ -1010,7 +1005,7 @@ pub const Inst = struct {
 
         pub fn toIndexAllowNone(ref: Ref) ?Index {
             return switch (ref) {
-                .var_args_param_type, .none => null,
+                .none => null,
                 else => if (@intFromEnum(ref) >> 31 != 0)
                     @enumFromInt(@as(u31, @truncate(@intFromEnum(ref))))
                 else
@@ -1476,8 +1471,8 @@ pub fn typeOfIndex(air: *const Air, inst: Air.Inst.Index, ip: *const InternPool)
         .save_err_return_trace_index,
         => return Type.usize,
 
-        .wasm_memory_grow => return Type.i32,
-        .wasm_memory_size => return Type.u32,
+        .wasm_memory_grow => return Type.isize,
+        .wasm_memory_size => return Type.usize,
 
         .int_from_bool => return Type.u1,
 
@@ -1557,7 +1552,6 @@ pub fn deinit(air: *Air, gpa: std.mem.Allocator) void {
 
 pub fn internedToRef(ip_index: InternPool.Index) Inst.Ref {
     return switch (ip_index) {
-        .var_args_param_type => .var_args_param_type,
         .none => .none,
         else => {
             assert(@intFromEnum(ip_index) >> 31 == 0);
diff --git a/src/Compilation.zig b/src/Compilation.zig
index 7af3d7bfd1..62545091ca 100644
--- a/src/Compilation.zig
+++ b/src/Compilation.zig
@@ -5091,7 +5091,7 @@ fn spawnZigRc(
     }
 }
 
-pub fn tmpFilePath(comp: *Compilation, ally: Allocator, suffix: []const u8) error{OutOfMemory}![]const u8 {
+pub fn tmpFilePath(comp: Compilation, ally: Allocator, suffix: []const u8) error{OutOfMemory}![]const u8 {
     const s = std.fs.path.sep_str;
     const rand_int = std.crypto.random.int(u64);
     if (comp.local_cache_directory.path) |p| {
@@ -5894,14 +5894,16 @@ pub fn lockAndSetMiscFailure(
     return setMiscFailure(comp, tag, format, args);
 }
 
-fn parseLldStderr(comp: *Compilation, comptime prefix: []const u8, stderr: []const u8) Allocator.Error!void {
+fn parseLldStderr(comp: *Compilation, prefix: []const u8, stderr: []const u8) Allocator.Error!void {
     var context_lines = std.ArrayList([]const u8).init(comp.gpa);
     defer context_lines.deinit();
 
     var current_err: ?*LldError = null;
     var lines = mem.splitSequence(u8, stderr, if (builtin.os.tag == .windows) "\r\n" else "\n");
     while (lines.next()) |line| {
-        if (mem.startsWith(u8, line, prefix ++ ":")) {
+        if (line.len > prefix.len + ":".len and
+            mem.eql(u8, line[0..prefix.len], prefix) and line[prefix.len] == ':')
+        {
             if (current_err) |err| {
                 err.context_lines = try context_lines.toOwnedSlice();
             }
@@ -5933,7 +5935,7 @@ fn parseLldStderr(comp: *Compilation, comptime prefix: []const u8, stderr: []con
     }
 }
 
-pub fn lockAndParseLldStderr(comp: *Compilation, comptime prefix: []const u8, stderr: []const u8) void {
+pub fn lockAndParseLldStderr(comp: *Compilation, prefix: []const u8, stderr: []const u8) void {
     comp.mutex.lock();
     defer comp.mutex.unlock();
 
diff --git a/src/InternPool.zig b/src/InternPool.zig
index e62bdc8499..b6d5e77f53 100644
--- a/src/InternPool.zig
+++ b/src/InternPool.zig
@@ -1921,7 +1921,7 @@ pub const LoadedUnionType = struct {
         return self.flagsPtr(ip).layout;
     }
 
-    pub fn fieldAlign(self: LoadedUnionType, ip: *const InternPool, field_index: u32) Alignment {
+    pub fn fieldAlign(self: LoadedUnionType, ip: *const InternPool, field_index: usize) Alignment {
         if (self.field_aligns.len == 0) return .none;
         return self.field_aligns.get(ip)[field_index];
     }
@@ -2087,41 +2087,41 @@ pub const LoadedStructType = struct {
 
     /// Returns the already-existing field with the same name, if any.
     pub fn addFieldName(
-        self: @This(),
+        self: LoadedStructType,
         ip: *InternPool,
         name: NullTerminatedString,
     ) ?u32 {
         return ip.addFieldName(self.names_map.unwrap().?, self.field_names.start, name);
     }
 
-    pub fn fieldAlign(s: @This(), ip: *const InternPool, i: usize) Alignment {
+    pub fn fieldAlign(s: LoadedStructType, ip: *const InternPool, i: usize) Alignment {
         if (s.field_aligns.len == 0) return .none;
         return s.field_aligns.get(ip)[i];
     }
 
-    pub fn fieldInit(s: @This(), ip: *const InternPool, i: usize) Index {
+    pub fn fieldInit(s: LoadedStructType, ip: *const InternPool, i: usize) Index {
         if (s.field_inits.len == 0) return .none;
         assert(s.haveFieldInits(ip));
         return s.field_inits.get(ip)[i];
     }
 
     /// Returns `none` in the case the struct is a tuple.
-    pub fn fieldName(s: @This(), ip: *const InternPool, i: usize) OptionalNullTerminatedString {
+    pub fn fieldName(s: LoadedStructType, ip: *const InternPool, i: usize) OptionalNullTerminatedString {
         if (s.field_names.len == 0) return .none;
         return s.field_names.get(ip)[i].toOptional();
     }
 
-    pub fn fieldIsComptime(s: @This(), ip: *const InternPool, i: usize) bool {
+    pub fn fieldIsComptime(s: LoadedStructType, ip: *const InternPool, i: usize) bool {
         return s.comptime_bits.getBit(ip, i);
     }
 
-    pub fn setFieldComptime(s: @This(), ip: *InternPool, i: usize) void {
+    pub fn setFieldComptime(s: LoadedStructType, ip: *InternPool, i: usize) void {
         s.comptime_bits.setBit(ip, i);
     }
 
     /// Reads the non-opv flag calculated during AstGen. Used to short-circuit more
     /// complicated logic.
-    pub fn knownNonOpv(s: @This(), ip: *InternPool) bool {
+    pub fn knownNonOpv(s: LoadedStructType, ip: *InternPool) bool {
         return switch (s.layout) {
             .@"packed" => false,
             .auto, .@"extern" => s.flagsPtr(ip).known_non_opv,
@@ -2130,7 +2130,7 @@ pub const LoadedStructType = struct {
 
     /// The returned pointer expires with any addition to the `InternPool`.
     /// Asserts the struct is not packed.
-    pub fn flagsPtr(self: @This(), ip: *const InternPool) *Tag.TypeStruct.Flags {
+    pub fn flagsPtr(self: LoadedStructType, ip: *const InternPool) *Tag.TypeStruct.Flags {
         assert(self.layout != .@"packed");
         const flags_field_index = std.meta.fieldIndex(Tag.TypeStruct, "flags").?;
         return @ptrCast(&ip.extra.items[self.extra_index + flags_field_index]);
@@ -2138,13 +2138,13 @@ pub const LoadedStructType = struct {
 
     /// The returned pointer expires with any addition to the `InternPool`.
     /// Asserts that the struct is packed.
-    pub fn packedFlagsPtr(self: @This(), ip: *const InternPool) *Tag.TypeStructPacked.Flags {
+    pub fn packedFlagsPtr(self: LoadedStructType, ip: *const InternPool) *Tag.TypeStructPacked.Flags {
         assert(self.layout == .@"packed");
         const flags_field_index = std.meta.fieldIndex(Tag.TypeStructPacked, "flags").?;
         return @ptrCast(&ip.extra.items[self.extra_index + flags_field_index]);
     }
 
-    pub fn assumeRuntimeBitsIfFieldTypesWip(s: @This(), ip: *InternPool) bool {
+    pub fn assumeRuntimeBitsIfFieldTypesWip(s: LoadedStructType, ip: *InternPool) bool {
         if (s.layout == .@"packed") return false;
         const flags_ptr = s.flagsPtr(ip);
         if (flags_ptr.field_types_wip) {
@@ -2154,7 +2154,7 @@ pub const LoadedStructType = struct {
         return false;
     }
 
-    pub fn setTypesWip(s: @This(), ip: *InternPool) bool {
+    pub fn setTypesWip(s: LoadedStructType, ip: *InternPool) bool {
         if (s.layout == .@"packed") return false;
         const flags_ptr = s.flagsPtr(ip);
         if (flags_ptr.field_types_wip) return true;
@@ -2162,12 +2162,12 @@ pub const LoadedStructType = struct {
         return false;
     }
 
-    pub fn clearTypesWip(s: @This(), ip: *InternPool) void {
+    pub fn clearTypesWip(s: LoadedStructType, ip: *InternPool) void {
         if (s.layout == .@"packed") return;
         s.flagsPtr(ip).field_types_wip = false;
     }
 
-    pub fn setLayoutWip(s: @This(), ip: *InternPool) bool {
+    pub fn setLayoutWip(s: LoadedStructType, ip: *InternPool) bool {
         if (s.layout == .@"packed") return false;
         const flags_ptr = s.flagsPtr(ip);
         if (flags_ptr.layout_wip) return true;
@@ -2175,12 +2175,12 @@ pub const LoadedStructType = struct {
         return false;
     }
 
-    pub fn clearLayoutWip(s: @This(), ip: *InternPool) void {
+    pub fn clearLayoutWip(s: LoadedStructType, ip: *InternPool) void {
         if (s.layout == .@"packed") return;
         s.flagsPtr(ip).layout_wip = false;
     }
 
-    pub fn setAlignmentWip(s: @This(), ip: *InternPool) bool {
+    pub fn setAlignmentWip(s: LoadedStructType, ip: *InternPool) bool {
         if (s.layout == .@"packed") return false;
         const flags_ptr = s.flagsPtr(ip);
         if (flags_ptr.alignment_wip) return true;
@@ -2188,12 +2188,12 @@ pub const LoadedStructType = struct {
         return false;
     }
 
-    pub fn clearAlignmentWip(s: @This(), ip: *InternPool) void {
+    pub fn clearAlignmentWip(s: LoadedStructType, ip: *InternPool) void {
         if (s.layout == .@"packed") return;
         s.flagsPtr(ip).alignment_wip = false;
     }
 
-    pub fn setInitsWip(s: @This(), ip: *InternPool) bool {
+    pub fn setInitsWip(s: LoadedStructType, ip: *InternPool) bool {
         switch (s.layout) {
             .@"packed" => {
                 const flag = &s.packedFlagsPtr(ip).field_inits_wip;
@@ -2210,14 +2210,14 @@ pub const LoadedStructType = struct {
         }
     }
 
-    pub fn clearInitsWip(s: @This(), ip: *InternPool) void {
+    pub fn clearInitsWip(s: LoadedStructType, ip: *InternPool) void {
         switch (s.layout) {
             .@"packed" => s.packedFlagsPtr(ip).field_inits_wip = false,
             .auto, .@"extern" => s.flagsPtr(ip).field_inits_wip = false,
         }
     }
 
-    pub fn setFullyResolved(s: @This(), ip: *InternPool) bool {
+    pub fn setFullyResolved(s: LoadedStructType, ip: *InternPool) bool {
         if (s.layout == .@"packed") return true;
         const flags_ptr = s.flagsPtr(ip);
         if (flags_ptr.fully_resolved) return true;
@@ -2225,13 +2225,13 @@ pub const LoadedStructType = struct {
         return false;
     }
 
-    pub fn clearFullyResolved(s: @This(), ip: *InternPool) void {
+    pub fn clearFullyResolved(s: LoadedStructType, ip: *InternPool) void {
         s.flagsPtr(ip).fully_resolved = false;
     }
 
     /// The returned pointer expires with any addition to the `InternPool`.
     /// Asserts the struct is not packed.
-    pub fn size(self: @This(), ip: *InternPool) *u32 {
+    pub fn size(self: LoadedStructType, ip: *InternPool) *u32 {
         assert(self.layout != .@"packed");
         const size_field_index = std.meta.fieldIndex(Tag.TypeStruct, "size").?;
         return @ptrCast(&ip.extra.items[self.extra_index + size_field_index]);
@@ -2241,50 +2241,50 @@ pub const LoadedStructType = struct {
     /// this type or the user specifies it, it is stored here. This will be
     /// set to `none` until the layout is resolved.
     /// Asserts the struct is packed.
-    pub fn backingIntType(s: @This(), ip: *const InternPool) *Index {
+    pub fn backingIntType(s: LoadedStructType, ip: *const InternPool) *Index {
         assert(s.layout == .@"packed");
         const field_index = std.meta.fieldIndex(Tag.TypeStructPacked, "backing_int_ty").?;
         return @ptrCast(&ip.extra.items[s.extra_index + field_index]);
     }
 
     /// Asserts the struct is not packed.
-    pub fn setZirIndex(s: @This(), ip: *InternPool, new_zir_index: TrackedInst.Index.Optional) void {
+    pub fn setZirIndex(s: LoadedStructType, ip: *InternPool, new_zir_index: TrackedInst.Index.Optional) void {
         assert(s.layout != .@"packed");
         const field_index = std.meta.fieldIndex(Tag.TypeStruct, "zir_index").?;
         ip.extra.items[s.extra_index + field_index] = @intFromEnum(new_zir_index);
     }
 
-    pub fn haveFieldTypes(s: @This(), ip: *const InternPool) bool {
+    pub fn haveFieldTypes(s: LoadedStructType, ip: *const InternPool) bool {
         const types = s.field_types.get(ip);
         return types.len == 0 or types[0] != .none;
     }
 
-    pub fn haveFieldInits(s: @This(), ip: *const InternPool) bool {
+    pub fn haveFieldInits(s: LoadedStructType, ip: *const InternPool) bool {
         return switch (s.layout) {
             .@"packed" => s.packedFlagsPtr(ip).inits_resolved,
             .auto, .@"extern" => s.flagsPtr(ip).inits_resolved,
         };
     }
 
-    pub fn setHaveFieldInits(s: @This(), ip: *InternPool) void {
+    pub fn setHaveFieldInits(s: LoadedStructType, ip: *InternPool) void {
         switch (s.layout) {
             .@"packed" => s.packedFlagsPtr(ip).inits_resolved = true,
             .auto, .@"extern" => s.flagsPtr(ip).inits_resolved = true,
         }
     }
 
-    pub fn haveLayout(s: @This(), ip: *InternPool) bool {
+    pub fn haveLayout(s: LoadedStructType, ip: *InternPool) bool {
         return switch (s.layout) {
             .@"packed" => s.backingIntType(ip).* != .none,
             .auto, .@"extern" => s.flagsPtr(ip).layout_resolved,
         };
     }
 
-    pub fn isTuple(s: @This(), ip: *InternPool) bool {
+    pub fn isTuple(s: LoadedStructType, ip: *InternPool) bool {
         return s.layout != .@"packed" and s.flagsPtr(ip).is_tuple;
     }
 
-    pub fn hasReorderedFields(s: @This()) bool {
+    pub fn hasReorderedFields(s: LoadedStructType) bool {
         return s.layout == .auto;
     }
 
@@ -2318,7 +2318,7 @@ pub const LoadedStructType = struct {
     /// Iterates over non-comptime fields in the order they are laid out in memory at runtime.
     /// May or may not include zero-bit fields.
     /// Asserts the struct is not packed.
-    pub fn iterateRuntimeOrder(s: @This(), ip: *InternPool) RuntimeOrderIterator {
+    pub fn iterateRuntimeOrder(s: LoadedStructType, ip: *InternPool) RuntimeOrderIterator {
         assert(s.layout != .@"packed");
         return .{
             .ip = ip,
@@ -2358,7 +2358,7 @@ pub const LoadedStructType = struct {
         }
     };
 
-    pub fn iterateRuntimeOrderReverse(s: @This(), ip: *InternPool) ReverseRuntimeOrderIterator {
+    pub fn iterateRuntimeOrderReverse(s: LoadedStructType, ip: *InternPool) ReverseRuntimeOrderIterator {
         assert(s.layout != .@"packed");
         return .{
             .ip = ip,
@@ -2818,7 +2818,6 @@ pub const Index = enum(u32) {
     generic_poison,
 
     /// Used by Air/Sema only.
-    var_args_param_type = std.math.maxInt(u32) - 1,
     none = std.math.maxInt(u32),
 
     _,
@@ -8938,7 +8937,6 @@ pub fn typeOf(ip: *const InternPool, index: Index) Index {
             .memoized_call => unreachable,
         },
 
-        .var_args_param_type => unreachable,
         .none => unreachable,
     };
 }
@@ -9153,8 +9151,6 @@ pub fn zigTypeTagOrPoison(ip: *const InternPool, index: Index) error{GenericPois
         .empty_struct => unreachable,
         .generic_poison => unreachable,
 
-        .var_args_param_type => unreachable, // special tag
-
         _ => switch (ip.items.items(.tag)[@intFromEnum(index)]) {
             .removed => unreachable,
 
diff --git a/src/Module.zig b/src/Module.zig
index 320627a129..004ee89e91 100644
--- a/src/Module.zig
+++ b/src/Module.zig
@@ -6140,18 +6140,18 @@ pub const UnionLayout = struct {
     padding: u32,
 };
 
-pub fn getUnionLayout(mod: *Module, u: InternPool.LoadedUnionType) UnionLayout {
+pub fn getUnionLayout(mod: *Module, loaded_union: InternPool.LoadedUnionType) UnionLayout {
     const ip = &mod.intern_pool;
-    assert(u.haveLayout(ip));
+    assert(loaded_union.haveLayout(ip));
     var most_aligned_field: u32 = undefined;
     var most_aligned_field_size: u64 = undefined;
     var biggest_field: u32 = undefined;
     var payload_size: u64 = 0;
     var payload_align: Alignment = .@"1";
-    for (u.field_types.get(ip), 0..) |field_ty, i| {
+    for (loaded_union.field_types.get(ip), 0..) |field_ty, field_index| {
         if (!Type.fromInterned(field_ty).hasRuntimeBitsIgnoreComptime(mod)) continue;
 
-        const explicit_align = u.fieldAlign(ip, @intCast(i));
+        const explicit_align = loaded_union.fieldAlign(ip, field_index);
         const field_align = if (explicit_align != .none)
             explicit_align
         else
@@ -6159,16 +6159,16 @@ pub fn getUnionLayout(mod: *Module, u: InternPool.LoadedUnionType) UnionLayout {
         const field_size = Type.fromInterned(field_ty).abiSize(mod);
         if (field_size > payload_size) {
             payload_size = field_size;
-            biggest_field = @intCast(i);
+            biggest_field = @intCast(field_index);
         }
         if (field_align.compare(.gte, payload_align)) {
             payload_align = field_align;
-            most_aligned_field = @intCast(i);
+            most_aligned_field = @intCast(field_index);
             most_aligned_field_size = field_size;
         }
     }
-    const have_tag = u.flagsPtr(ip).runtime_tag.hasTag();
-    if (!have_tag or !Type.fromInterned(u.enum_tag_ty).hasRuntimeBits(mod)) {
+    const have_tag = loaded_union.flagsPtr(ip).runtime_tag.hasTag();
+    if (!have_tag or !Type.fromInterned(loaded_union.enum_tag_ty).hasRuntimeBits(mod)) {
         return .{
             .abi_size = payload_align.forward(payload_size),
             .abi_align = payload_align,
@@ -6183,10 +6183,10 @@ pub fn getUnionLayout(mod: *Module, u: InternPool.LoadedUnionType) UnionLayout {
         };
     }
 
-    const tag_size = Type.fromInterned(u.enum_tag_ty).abiSize(mod);
-    const tag_align = Type.fromInterned(u.enum_tag_ty).abiAlignment(mod).max(.@"1");
+    const tag_size = Type.fromInterned(loaded_union.enum_tag_ty).abiSize(mod);
+    const tag_align = Type.fromInterned(loaded_union.enum_tag_ty).abiAlignment(mod).max(.@"1");
     return .{
-        .abi_size = u.size(ip).*,
+        .abi_size = loaded_union.size(ip).*,
         .abi_align = tag_align.max(payload_align),
         .most_aligned_field = most_aligned_field,
         .most_aligned_field_size = most_aligned_field_size,
@@ -6195,24 +6195,24 @@ pub fn getUnionLayout(mod: *Module, u: InternPool.LoadedUnionType) UnionLayout {
         .payload_align = payload_align,
         .tag_align = tag_align,
         .tag_size = tag_size,
-        .padding = u.padding(ip).*,
+        .padding = loaded_union.padding(ip).*,
     };
 }
 
-pub fn unionAbiSize(mod: *Module, u: InternPool.LoadedUnionType) u64 {
-    return mod.getUnionLayout(u).abi_size;
+pub fn unionAbiSize(mod: *Module, loaded_union: InternPool.LoadedUnionType) u64 {
+    return mod.getUnionLayout(loaded_union).abi_size;
 }
 
 /// Returns 0 if the union is represented with 0 bits at runtime.
-pub fn unionAbiAlignment(mod: *Module, u: InternPool.LoadedUnionType) Alignment {
+pub fn unionAbiAlignment(mod: *Module, loaded_union: InternPool.LoadedUnionType) Alignment {
     const ip = &mod.intern_pool;
-    const have_tag = u.flagsPtr(ip).runtime_tag.hasTag();
+    const have_tag = loaded_union.flagsPtr(ip).runtime_tag.hasTag();
     var max_align: Alignment = .none;
-    if (have_tag) max_align = Type.fromInterned(u.enum_tag_ty).abiAlignment(mod);
-    for (u.field_types.get(ip), 0..) |field_ty, field_index| {
+    if (have_tag) max_align = Type.fromInterned(loaded_union.enum_tag_ty).abiAlignment(mod);
+    for (loaded_union.field_types.get(ip), 0..) |field_ty, field_index| {
         if (!Type.fromInterned(field_ty).hasRuntimeBits(mod)) continue;
 
-        const field_align = mod.unionFieldNormalAlignment(u, @intCast(field_index));
+        const field_align = mod.unionFieldNormalAlignment(loaded_union, @intCast(field_index));
         max_align = max_align.max(field_align);
     }
     return max_align;
@@ -6221,20 +6221,20 @@ pub fn unionAbiAlignment(mod: *Module, u: InternPool.LoadedUnionType) Alignment
 /// Returns the field alignment, assuming the union is not packed.
 /// Keep implementation in sync with `Sema.unionFieldAlignment`.
 /// Prefer to call that function instead of this one during Sema.
-pub fn unionFieldNormalAlignment(mod: *Module, u: InternPool.LoadedUnionType, field_index: u32) Alignment {
+pub fn unionFieldNormalAlignment(mod: *Module, loaded_union: InternPool.LoadedUnionType, field_index: u32) Alignment {
     const ip = &mod.intern_pool;
-    const field_align = u.fieldAlign(ip, field_index);
+    const field_align = loaded_union.fieldAlign(ip, field_index);
     if (field_align != .none) return field_align;
-    const field_ty = Type.fromInterned(u.field_types.get(ip)[field_index]);
+    const field_ty = Type.fromInterned(loaded_union.field_types.get(ip)[field_index]);
     return field_ty.abiAlignment(mod);
 }
 
 /// Returns the index of the active field, given the current tag value
-pub fn unionTagFieldIndex(mod: *Module, u: InternPool.LoadedUnionType, enum_tag: Value) ?u32 {
+pub fn unionTagFieldIndex(mod: *Module, loaded_union: InternPool.LoadedUnionType, enum_tag: Value) ?u32 {
     const ip = &mod.intern_pool;
     if (enum_tag.toIntern() == .none) return null;
-    assert(ip.typeOf(enum_tag.toIntern()) == u.enum_tag_ty);
-    return u.loadTagType(ip).tagValueIndex(ip, enum_tag.toIntern());
+    assert(ip.typeOf(enum_tag.toIntern()) == loaded_union.enum_tag_ty);
+    return loaded_union.loadTagType(ip).tagValueIndex(ip, enum_tag.toIntern());
 }
 
 /// Returns the field alignment of a non-packed struct in byte units.
diff --git a/src/Sema.zig b/src/Sema.zig
index d80cf81888..e6c0f62b0a 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -1901,7 +1901,6 @@ pub fn resolveConstStringIntern(
 
 pub fn resolveType(sema: *Sema, block: *Block, src: LazySrcLoc, zir_ref: Zir.Inst.Ref) !Type {
     const air_inst = try sema.resolveInst(zir_ref);
-    assert(air_inst != .var_args_param_type);
     const ty = try sema.analyzeAsType(block, src, air_inst);
     if (ty.isGenericPoison()) return error.GenericPoison;
     return ty;
@@ -4572,12 +4571,10 @@ fn zirValidateRefTy(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileErr
     const src = un_tok.src();
     // In case of GenericPoison, we don't actually have a type, so this will be
     // treated as an untyped address-of operator.
-    if (un_tok.operand == .var_args_param_type) return;
     const operand_air_inst = sema.resolveInst(un_tok.operand) catch |err| switch (err) {
         error.GenericPoison => return,
         else => |e| return e,
     };
-    if (operand_air_inst == .var_args_param_type) return;
     const ty_operand = sema.analyzeAsType(block, src, operand_air_inst) catch |err| switch (err) {
         error.GenericPoison => return,
         else => |e| return e,
@@ -7363,7 +7360,7 @@ const CallArgsInfo = union(enum) {
     }
 
     /// Analyzes the arg at `arg_index` and coerces it to `param_ty`.
-    /// `param_ty` may be `generic_poison` or `var_args_param`.
+    /// `param_ty` may be `generic_poison`. A value of `null` indicates a varargs parameter.
     /// `func_ty_info` may be the type before instantiation, even if a generic
     /// instantiation has been partially completed.
     fn analyzeArg(
@@ -7371,16 +7368,16 @@ const CallArgsInfo = union(enum) {
         sema: *Sema,
         block: *Block,
         arg_index: usize,
-        param_ty: Type,
+        maybe_param_ty: ?Type,
         func_ty_info: InternPool.Key.FuncType,
         func_inst: Air.Inst.Ref,
     ) CompileError!Air.Inst.Ref {
         const mod = sema.mod;
         const param_count = func_ty_info.param_types.len;
-        switch (param_ty.toIntern()) {
-            .generic_poison_type, .var_args_param_type => {},
+        if (maybe_param_ty) |param_ty| switch (param_ty.toIntern()) {
+            .generic_poison_type => {},
             else => try sema.queueFullTypeResolution(param_ty),
-        }
+        };
         const uncoerced_arg: Air.Inst.Ref = switch (cai) {
             inline .resolved, .call_builtin => |resolved| resolved.args[arg_index],
             .zir_call => |zir_call| arg_val: {
@@ -7409,7 +7406,8 @@ const CallArgsInfo = union(enum) {
                     // TODO set comptime_reason
                 }
                 // Give the arg its result type
-                sema.inst_map.putAssumeCapacity(zir_call.call_inst, Air.internedToRef(param_ty.toIntern()));
+                const provide_param_ty = if (maybe_param_ty) |t| t else Type.generic_poison;
+                sema.inst_map.putAssumeCapacity(zir_call.call_inst, Air.internedToRef(provide_param_ty.toIntern()));
                 // Resolve the arg!
                 const uncoerced_arg = try sema.resolveInlineBody(block, arg_body, zir_call.call_inst);
 
@@ -7426,9 +7424,11 @@ const CallArgsInfo = union(enum) {
                 break :arg_val uncoerced_arg;
             },
         };
+        const param_ty = maybe_param_ty orelse {
+            return sema.coerceVarArgParam(block, uncoerced_arg, cai.argSrc(block, arg_index));
+        };
         switch (param_ty.toIntern()) {
             .generic_poison_type => return uncoerced_arg,
-            .var_args_param_type => return sema.coerceVarArgParam(block, uncoerced_arg, cai.argSrc(block, arg_index)),
             else => return sema.coerceExtra(
                 block,
                 param_ty,
@@ -7970,10 +7970,10 @@ fn analyzeCall(
         const args = try sema.arena.alloc(Air.Inst.Ref, args_info.count());
         for (args, 0..) |*arg_out, arg_idx| {
             // Non-generic, so param types are already resolved
-            const param_ty = if (arg_idx < func_ty_info.param_types.len) ty: {
+            const param_ty: ?Type = if (arg_idx < func_ty_info.param_types.len) ty: {
                 break :ty Type.fromInterned(func_ty_info.param_types.get(ip)[arg_idx]);
-            } else Type.fromInterned(InternPool.Index.var_args_param_type);
-            assert(!param_ty.isGenericPoison());
+            } else null;
+            if (param_ty) |t| assert(!t.isGenericPoison());
             arg_out.* = try args_info.analyzeArg(sema, block, arg_idx, param_ty, func_ty_info, func);
             try sema.validateRuntimeValue(block, args_info.argSrc(block, arg_idx), arg_out.*);
             if (sema.typeOf(arg_out.*).zigTypeTag(mod) == .NoReturn) {
@@ -9700,6 +9700,18 @@ fn funcCommon(
         {
             return sema.fail(block, param_src, "non-pointer parameter declared noalias", .{});
         }
+        switch (cc_resolved) {
+            .Interrupt => if (target.cpu.arch.isX86()) {
+                const err_code_size = target.ptrBitWidth();
+                switch (i) {
+                    0 => if (param_ty.zigTypeTag(mod) != .Pointer) return sema.fail(block, param_src, "first parameter of function with 'Interrupt' calling convention must be a pointer type", .{}),
+                    1 => if (param_ty.bitSize(mod) != err_code_size) return sema.fail(block, param_src, "second parameter of function with 'Interrupt' calling convention must be a {d}-bit integer", .{err_code_size}),
+                    else => return sema.fail(block, param_src, "'Interrupt' calling convention supports up to 2 parameters, found {d}", .{i + 1}),
+                }
+            } else return sema.fail(block, param_src, "parameters are not allowed with 'Interrupt' calling convention", .{}),
+            .Signal => return sema.fail(block, param_src, "parameters are not allowed with 'Signal' calling convention", .{}),
+            else => {},
+        }
     }
 
     var ret_ty_requires_comptime = false;
@@ -10005,6 +10017,16 @@ fn finishFunc(
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
+    switch (cc_resolved) {
+        .Interrupt, .Signal => if (return_type.zigTypeTag(mod) != .Void and return_type.zigTypeTag(mod) != .NoReturn) {
+            return sema.fail(block, ret_ty_src, "function with calling convention '{s}' must return 'void' or 'noreturn'", .{@tagName(cc_resolved)});
+        },
+        .Inline => if (is_noinline) {
+            return sema.fail(block, cc_src, "'noinline' function cannot have callconv 'Inline'", .{});
+        },
+        else => {},
+    }
+
     const arch = target.cpu.arch;
     if (@as(?[]const u8, switch (cc_resolved) {
         .Unspecified, .C, .Naked, .Async, .Inline => null,
@@ -10048,11 +10070,7 @@ fn finishFunc(
         });
     }
 
-    if (cc_resolved == .Inline and is_noinline) {
-        return sema.fail(block, cc_src, "'noinline' function cannot have callconv 'Inline'", .{});
-    }
     if (is_generic and sema.no_partial_func_ty) return error.GenericPoison;
-
     if (!final_is_generic and sema.wantErrorReturnTracing(return_type)) {
         // Make sure that StackTrace's fields are resolved so that the backend can
         // lower this fn type.
@@ -10205,12 +10223,10 @@ fn analyzeAs(
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const operand = try sema.resolveInst(zir_operand);
-    if (zir_dest_type == .var_args_param_type) return operand;
     const operand_air_inst = sema.resolveInst(zir_dest_type) catch |err| switch (err) {
         error.GenericPoison => return operand,
         else => |e| return e,
     };
-    if (operand_air_inst == .var_args_param_type) return operand;
     const dest_ty = sema.analyzeAsType(block, src, operand_air_inst) catch |err| switch (err) {
         error.GenericPoison => return operand,
         else => |e| return e,
@@ -22688,7 +22704,16 @@ fn zirPtrFromInt(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!
             .storage = .{ .elems = new_elems },
         } }));
     }
+    if (try sema.typeRequiresComptime(ptr_ty)) {
+        return sema.failWithOwnedErrorMsg(block, msg: {
+            const msg = try sema.errMsg(block, src, "pointer to comptime-only type '{}' must be comptime-known, but operand is runtime-known", .{ptr_ty.fmt(mod)});
+            errdefer msg.destroy(sema.gpa);
 
+            const src_decl = mod.declPtr(block.src_decl);
+            try sema.explainWhyTypeIsComptime(msg, src_decl.toSrcLoc(src, mod), ptr_ty);
+            break :msg msg;
+        });
+    }
     try sema.requireRuntimeBlock(block, src, operand_src);
     if (!is_vector) {
         if (block.wantSafety() and (try sema.typeHasRuntimeBits(elem_ty) or elem_ty.zigTypeTag(mod) == .Fn)) {
@@ -24274,6 +24299,14 @@ fn zirSplat(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.I
 
     if (!dest_ty.isVector(mod)) return sema.fail(block, src, "expected vector type, found '{}'", .{dest_ty.fmt(mod)});
 
+    if (!dest_ty.hasRuntimeBits(mod)) {
+        const empty_aggregate = try mod.intern(.{ .aggregate = .{
+            .ty = dest_ty.toIntern(),
+            .storage = .{ .elems = &[_]InternPool.Index{} },
+        } });
+        return Air.internedToRef(empty_aggregate);
+    }
+
     const operand = try sema.resolveInst(extra.rhs);
     const scalar_ty = dest_ty.childType(mod);
     const scalar = try sema.coerce(block, scalar_ty, operand, scalar_src);
@@ -26211,7 +26244,7 @@ fn zirWasmMemoryGrow(
     const index: u32 = @intCast(try sema.resolveInt(block, index_src, extra.lhs, Type.u32, .{
         .needed_comptime_reason = "wasm memory size index must be comptime-known",
     }));
-    const delta = try sema.coerce(block, Type.u32, try sema.resolveInst(extra.rhs), delta_src);
+    const delta = try sema.coerce(block, Type.usize, try sema.resolveInst(extra.rhs), delta_src);
 
     try sema.requireRuntimeBlock(block, builtin_src, null);
     return block.addInst(.{
@@ -32507,7 +32540,7 @@ fn analyzeSlice(
                     const uncasted_end = try sema.analyzeArithmetic(block, .add, start, len, src, start_src, end_src, false);
                     break :end try sema.coerce(block, Type.usize, uncasted_end, end_src);
                 } else try sema.coerce(block, Type.usize, uncasted_end_opt, end_src);
-                if (try sema.resolveValue(end)) |end_val| {
+                if (try sema.resolveDefinedValue(block, end_src, end)) |end_val| {
                     const len_s_val = try mod.intValue(
                         Type.usize,
                         array_ty.arrayLenIncludingSentinel(mod),
@@ -35405,7 +35438,7 @@ pub fn resolveUnionAlignment(
         const field_ty = Type.fromInterned(union_type.field_types.get(ip)[field_index]);
         if (!(try sema.typeHasRuntimeBits(field_ty))) continue;
 
-        const explicit_align = union_type.fieldAlign(ip, @intCast(field_index));
+        const explicit_align = union_type.fieldAlign(ip, field_index);
         const field_align = if (explicit_align != .none)
             explicit_align
         else
@@ -35465,7 +35498,7 @@ fn resolveUnionLayout(sema: *Sema, ty: Type) CompileError!void {
             else => return err,
         });
 
-        const explicit_align = union_type.fieldAlign(ip, @intCast(field_index));
+        const explicit_align = union_type.fieldAlign(ip, field_index);
         const field_align = if (explicit_align != .none)
             explicit_align
         else
@@ -35635,8 +35668,6 @@ pub fn resolveTypeFields(sema: *Sema, ty: Type) CompileError!void {
     const ty_ip = ty.toIntern();
 
     switch (ty_ip) {
-        .var_args_param_type => unreachable,
-
         .none => unreachable,
 
         .u0_type,
@@ -37155,7 +37186,6 @@ pub fn typeHasOnePossibleValue(sema: *Sema, ty: Type) CompileError!?Value {
         .empty_struct,
         .generic_poison,
         // invalid
-        .var_args_param_type,
         .none,
         => unreachable,
 
diff --git a/src/arch/x86_64/CodeGen.zig b/src/arch/x86_64/CodeGen.zig
index 0681bc975d..7faf3d6d50 100644
--- a/src/arch/x86_64/CodeGen.zig
+++ b/src/arch/x86_64/CodeGen.zig
@@ -14316,7 +14316,7 @@ fn moveStrategy(self: *Self, ty: Type, class: Register.Class, aligned: bool) !Mo
         .mmx => {},
         .sse => switch (ty.zigTypeTag(mod)) {
             else => {
-                const classes = mem.sliceTo(&abi.classifySystemV(ty, mod, .other), .none);
+                const classes = mem.sliceTo(&abi.classifySystemV(ty, mod, self.target.*, .other), .none);
                 assert(std.mem.indexOfNone(abi.Class, classes, &.{
                     .integer, .sse, .memory, .float, .float_combine,
                 }) == null);
@@ -18450,7 +18450,7 @@ fn airVaArg(self: *Self, inst: Air.Inst.Index) !void {
             const overflow_arg_area: MCValue = .{ .indirect = .{ .reg = ptr_arg_list_reg, .off = 8 } };
             const reg_save_area: MCValue = .{ .indirect = .{ .reg = ptr_arg_list_reg, .off = 16 } };
 
-            const classes = mem.sliceTo(&abi.classifySystemV(promote_ty, mod, .arg), .none);
+            const classes = mem.sliceTo(&abi.classifySystemV(promote_ty, mod, self.target.*, .arg), .none);
             switch (classes[0]) {
                 .integer => {
                     assert(classes.len == 1);
@@ -18800,7 +18800,7 @@ fn resolveCallingConventionValues(
                 var ret_tracking_i: usize = 0;
 
                 const classes = switch (resolved_cc) {
-                    .SysV => mem.sliceTo(&abi.classifySystemV(ret_ty, mod, .ret), .none),
+                    .SysV => mem.sliceTo(&abi.classifySystemV(ret_ty, mod, self.target.*, .ret), .none),
                     .Win64 => &.{abi.classifyWindows(ret_ty, mod)},
                     else => unreachable,
                 };
@@ -18875,7 +18875,7 @@ fn resolveCallingConventionValues(
                 var arg_mcv_i: usize = 0;
 
                 const classes = switch (resolved_cc) {
-                    .SysV => mem.sliceTo(&abi.classifySystemV(ty, mod, .arg), .none),
+                    .SysV => mem.sliceTo(&abi.classifySystemV(ty, mod, self.target.*, .arg), .none),
                     .Win64 => &.{abi.classifyWindows(ty, mod)},
                     else => unreachable,
                 };
@@ -19090,7 +19090,7 @@ fn memSize(self: *Self, ty: Type) Memory.Size {
 
 fn splitType(self: *Self, ty: Type) ![2]Type {
     const mod = self.bin_file.comp.module.?;
-    const classes = mem.sliceTo(&abi.classifySystemV(ty, mod, .other), .none);
+    const classes = mem.sliceTo(&abi.classifySystemV(ty, mod, self.target.*, .other), .none);
     var parts: [2]Type = undefined;
     if (classes.len == 2) for (&parts, classes, 0..) |*part, class, part_i| {
         part.* = switch (class) {
diff --git a/src/arch/x86_64/abi.zig b/src/arch/x86_64/abi.zig
index c3ab91af8d..8c81ad9ed2 100644
--- a/src/arch/x86_64/abi.zig
+++ b/src/arch/x86_64/abi.zig
@@ -11,6 +11,37 @@ pub const Class = enum {
     float,
     float_combine,
     integer_per_element,
+
+    fn isX87(class: Class) bool {
+        return switch (class) {
+            .x87, .x87up, .complex_x87 => true,
+            else => false,
+        };
+    }
+
+    /// Combine a field class with the prev one.
+    fn combineSystemV(prev_class: Class, next_class: Class) Class {
+        // "If both classes are equal, this is the resulting class."
+        if (prev_class == next_class)
+            return if (prev_class == .float) .float_combine else prev_class;
+
+        // "If one of the classes is NO_CLASS, the resulting class
+        // is the other class."
+        if (prev_class == .none) return next_class;
+
+        // "If one of the classes is MEMORY, the result is the MEMORY class."
+        if (prev_class == .memory or next_class == .memory) return .memory;
+
+        // "If one of the classes is INTEGER, the result is the INTEGER."
+        if (prev_class == .integer or next_class == .integer) return .integer;
+
+        // "If one of the classes is X87, X87UP, COMPLEX_X87 class,
+        // MEMORY is used as class."
+        if (prev_class.isX87() or next_class.isX87()) return .memory;
+
+        // "Otherwise class SSE is used."
+        return .sse;
+    }
 };
 
 pub fn classifyWindows(ty: Type, zcu: *Zcu) Class {
@@ -69,9 +100,7 @@ pub const Context = enum { ret, arg, field, other };
 
 /// There are a maximum of 8 possible return slots. Returned values are in
 /// the beginning of the array; unused slots are filled with .none.
-pub fn classifySystemV(ty: Type, zcu: *Zcu, ctx: Context) [8]Class {
-    const ip = &zcu.intern_pool;
-    const target = zcu.getTarget();
+pub fn classifySystemV(ty: Type, zcu: *Zcu, target: std.Target, ctx: Context) [8]Class {
     const memory_class = [_]Class{
         .memory, .none, .none, .none,
         .none,   .none, .none, .none,
@@ -231,121 +260,30 @@ pub fn classifySystemV(ty: Type, zcu: *Zcu, ctx: Context) [8]Class {
             }
             return memory_class;
         },
-        .Struct => {
+        .Struct, .Union => {
             // "If the size of an object is larger than eight eightbytes, or
             // it contains unaligned fields, it has class MEMORY"
             // "If the size of the aggregate exceeds a single eightbyte, each is classified
             // separately.".
-            const loaded_struct = ip.loadStructType(ty.toIntern());
             const ty_size = ty.abiSize(zcu);
-            if (loaded_struct.layout == .@"packed") {
-                assert(ty_size <= 16);
-                result[0] = .integer;
-                if (ty_size > 8) result[1] = .integer;
-                return result;
+            switch (ty.containerLayout(zcu)) {
+                .auto, .@"extern" => {},
+                .@"packed" => {
+                    assert(ty_size <= 16);
+                    result[0] = .integer;
+                    if (ty_size > 8) result[1] = .integer;
+                    return result;
+                },
             }
             if (ty_size > 64)
                 return memory_class;
 
-            var byte_offset: u64 = 0;
-            classifySystemVStruct(&result, &byte_offset, loaded_struct, zcu);
-
-            // Post-merger cleanup
-
-            // "If one of the classes is MEMORY, the whole argument is passed in memory"
-            // "If X87UP is not preceded by X87, the whole argument is passed in memory."
-            var found_sseup = false;
-            for (result, 0..) |item, i| switch (item) {
-                .memory => return memory_class,
-                .x87up => if (i == 0 or result[i - 1] != .x87) return memory_class,
-                .sseup => found_sseup = true,
-                else => continue,
-            };
-            // "If the size of the aggregate exceeds two eightbytes and the first eight-
-            // byte isn’t SSE or any other eightbyte isn’t SSEUP, the whole argument
-            // is passed in memory."
-            if (ty_size > 16 and (result[0] != .sse or !found_sseup)) return memory_class;
-
-            // "If SSEUP is not preceded by SSE or SSEUP, it is converted to SSE."
-            for (&result, 0..) |*item, i| {
-                if (item.* == .sseup) switch (result[i - 1]) {
-                    .sse, .sseup => continue,
-                    else => item.* = .sse,
-                };
-            }
-            return result;
-        },
-        .Union => {
-            // "If the size of an object is larger than eight eightbytes, or
-            // it contains unaligned fields, it has class MEMORY"
-            // "If the size of the aggregate exceeds a single eightbyte, each is classified
-            // separately.".
-            const union_obj = zcu.typeToUnion(ty).?;
-            const ty_size = zcu.unionAbiSize(union_obj);
-            if (union_obj.getLayout(ip) == .@"packed") {
-                assert(ty_size <= 16);
-                result[0] = .integer;
-                if (ty_size > 8) result[1] = .integer;
-                return result;
-            }
-            if (ty_size > 64)
-                return memory_class;
-
-            for (union_obj.field_types.get(ip), 0..) |field_ty, field_index| {
-                const field_align = union_obj.fieldAlign(ip, @intCast(field_index));
-                if (field_align != .none and
-                    field_align.compare(.lt, Type.fromInterned(field_ty).abiAlignment(zcu)))
-                {
-                    return memory_class;
-                }
-                // Combine this field with the previous one.
-                const field_class = classifySystemV(Type.fromInterned(field_ty), zcu, .field);
-                for (&result, 0..) |*result_item, i| {
-                    const field_item = field_class[i];
-                    // "If both classes are equal, this is the resulting class."
-                    if (result_item.* == field_item) {
-                        continue;
-                    }
-
-                    // "If one of the classes is NO_CLASS, the resulting class
-                    // is the other class."
-                    if (result_item.* == .none) {
-                        result_item.* = field_item;
-                        continue;
-                    }
-                    if (field_item == .none) {
-                        continue;
-                    }
-
-                    // "If one of the classes is MEMORY, the result is the MEMORY class."
-                    if (result_item.* == .memory or field_item == .memory) {
-                        result_item.* = .memory;
-                        continue;
-                    }
-
-                    // "If one of the classes is INTEGER, the result is the INTEGER."
-                    if (result_item.* == .integer or field_item == .integer) {
-                        result_item.* = .integer;
-                        continue;
-                    }
-
-                    // "If one of the classes is X87, X87UP, COMPLEX_X87 class,
-                    // MEMORY is used as class."
-                    if (result_item.* == .x87 or
-                        result_item.* == .x87up or
-                        result_item.* == .complex_x87 or
-                        field_item == .x87 or
-                        field_item == .x87up or
-                        field_item == .complex_x87)
-                    {
-                        result_item.* = .memory;
-                        continue;
-                    }
-
-                    // "Otherwise class SSE is used."
-                    result_item.* = .sse;
-                }
-            }
+            _ = if (zcu.typeToStruct(ty)) |loaded_struct|
+                classifySystemVStruct(&result, 0, loaded_struct, zcu, target)
+            else if (zcu.typeToUnion(ty)) |loaded_union|
+                classifySystemVUnion(&result, 0, loaded_union, zcu, target)
+            else
+                unreachable;
 
             // Post-merger cleanup
 
@@ -391,78 +329,85 @@ pub fn classifySystemV(ty: Type, zcu: *Zcu, ctx: Context) [8]Class {
 
 fn classifySystemVStruct(
     result: *[8]Class,
-    byte_offset: *u64,
+    starting_byte_offset: u64,
     loaded_struct: InternPool.LoadedStructType,
     zcu: *Zcu,
-) void {
+    target: std.Target,
+) u64 {
     const ip = &zcu.intern_pool;
+    var byte_offset = starting_byte_offset;
     var field_it = loaded_struct.iterateRuntimeOrder(ip);
     while (field_it.next()) |field_index| {
         const field_ty = Type.fromInterned(loaded_struct.field_types.get(ip)[field_index]);
         const field_align = loaded_struct.fieldAlign(ip, field_index);
-        byte_offset.* = std.mem.alignForward(
+        byte_offset = std.mem.alignForward(
             u64,
-            byte_offset.*,
+            byte_offset,
             field_align.toByteUnits() orelse field_ty.abiAlignment(zcu).toByteUnits().?,
         );
         if (zcu.typeToStruct(field_ty)) |field_loaded_struct| {
-            if (field_loaded_struct.layout != .@"packed") {
-                classifySystemVStruct(result, byte_offset, field_loaded_struct, zcu);
-                continue;
+            switch (field_loaded_struct.layout) {
+                .auto, .@"extern" => {
+                    byte_offset = classifySystemVStruct(result, byte_offset, field_loaded_struct, zcu, target);
+                    continue;
+                },
+                .@"packed" => {},
+            }
+        } else if (zcu.typeToUnion(field_ty)) |field_loaded_union| {
+            switch (field_loaded_union.getLayout(ip)) {
+                .auto, .@"extern" => {
+                    byte_offset = classifySystemVUnion(result, byte_offset, field_loaded_union, zcu, target);
+                    continue;
+                },
+                .@"packed" => {},
             }
         }
-        const field_class = std.mem.sliceTo(&classifySystemV(field_ty, zcu, .field), .none);
-        const field_size = field_ty.abiSize(zcu);
-        combine: {
-            // Combine this field with the previous one.
-            const result_class = &result[@intCast(byte_offset.* / 8)];
-            // "If both classes are equal, this is the resulting class."
-            if (result_class.* == field_class[0]) {
-                if (result_class.* == .float) {
-                    result_class.* = .float_combine;
-                }
-                break :combine;
-            }
-
-            // "If one of the classes is NO_CLASS, the resulting class
-            // is the other class."
-            if (result_class.* == .none) {
-                result_class.* = field_class[0];
-                break :combine;
-            }
-            assert(field_class[0] != .none);
-
-            // "If one of the classes is MEMORY, the result is the MEMORY class."
-            if (result_class.* == .memory or field_class[0] == .memory) {
-                result_class.* = .memory;
-                break :combine;
-            }
-
-            // "If one of the classes is INTEGER, the result is the INTEGER."
-            if (result_class.* == .integer or field_class[0] == .integer) {
-                result_class.* = .integer;
-                break :combine;
-            }
-
-            // "If one of the classes is X87, X87UP, COMPLEX_X87 class,
-            // MEMORY is used as class."
-            if (result_class.* == .x87 or
-                result_class.* == .x87up or
-                result_class.* == .complex_x87 or
-                field_class[0] == .x87 or
-                field_class[0] == .x87up or
-                field_class[0] == .complex_x87)
-            {
-                result_class.* = .memory;
-                break :combine;
-            }
-
-            // "Otherwise class SSE is used."
-            result_class.* = .sse;
-        }
-        @memcpy(result[@intCast(byte_offset.* / 8 + 1)..][0 .. field_class.len - 1], field_class[1..]);
-        byte_offset.* += field_size;
+        const field_classes = std.mem.sliceTo(&classifySystemV(field_ty, zcu, target, .field), .none);
+        for (result[@intCast(byte_offset / 8)..][0..field_classes.len], field_classes) |*result_class, field_class|
+            result_class.* = result_class.combineSystemV(field_class);
+        byte_offset += field_ty.abiSize(zcu);
     }
+    const final_byte_offset = starting_byte_offset + loaded_struct.size(ip).*;
+    std.debug.assert(final_byte_offset == std.mem.alignForward(
+        u64,
+        byte_offset,
+        loaded_struct.flagsPtr(ip).alignment.toByteUnits().?,
+    ));
+    return final_byte_offset;
+}
+
+fn classifySystemVUnion(
+    result: *[8]Class,
+    starting_byte_offset: u64,
+    loaded_union: InternPool.LoadedUnionType,
+    zcu: *Zcu,
+    target: std.Target,
+) u64 {
+    const ip = &zcu.intern_pool;
+    for (0..loaded_union.field_types.len) |field_index| {
+        const field_ty = Type.fromInterned(loaded_union.field_types.get(ip)[field_index]);
+        if (zcu.typeToStruct(field_ty)) |field_loaded_struct| {
+            switch (field_loaded_struct.layout) {
+                .auto, .@"extern" => {
+                    _ = classifySystemVStruct(result, starting_byte_offset, field_loaded_struct, zcu, target);
+                    continue;
+                },
+                .@"packed" => {},
+            }
+        } else if (zcu.typeToUnion(field_ty)) |field_loaded_union| {
+            switch (field_loaded_union.getLayout(ip)) {
+                .auto, .@"extern" => {
+                    _ = classifySystemVUnion(result, starting_byte_offset, field_loaded_union, zcu, target);
+                    continue;
+                },
+                .@"packed" => {},
+            }
+        }
+        const field_classes = std.mem.sliceTo(&classifySystemV(field_ty, zcu, target, .field), .none);
+        for (result[@intCast(starting_byte_offset / 8)..][0..field_classes.len], field_classes) |*result_class, field_class|
+            result_class.* = result_class.combineSystemV(field_class);
+    }
+    return starting_byte_offset + loaded_union.size(ip).*;
 }
 
 pub const SysV = struct {
diff --git a/src/codegen/c.zig b/src/codegen/c.zig
index 1725658a37..6a17cb3970 100644
--- a/src/codegen/c.zig
+++ b/src/codegen/c.zig
@@ -3176,6 +3176,7 @@ fn genBodyInner(f: *Function, body: []const Air.Inst.Index) error{ AnalysisFail,
     const zcu = f.object.dg.zcu;
     const ip = &zcu.intern_pool;
     const air_tags = f.air.instructions.items(.tag);
+    const air_datas = f.air.instructions.items(.data);
 
     for (body) |inst| {
         if (f.liveness.isUnused(inst) and !f.air.mustLower(inst, ip))
@@ -3203,23 +3204,23 @@ fn genBodyInner(f: *Function, body: []const Air.Inst.Index) error{ AnalysisFail,
             .sub => try airBinOp(f, inst, "-", "sub", .none),
             .mul => try airBinOp(f, inst, "*", "mul", .none),
 
-            .neg => try airFloatNeg(f, inst),
+            .neg => try airUnBuiltinCall(f, inst, air_datas[@intFromEnum(inst)].un_op, "neg", .none),
             .div_float => try airBinBuiltinCall(f, inst, "div", .none),
 
             .div_trunc, .div_exact => try airBinOp(f, inst, "/", "div_trunc", .none),
             .rem => blk: {
-                const bin_op = f.air.instructions.items(.data)[@intFromEnum(inst)].bin_op;
+                const bin_op = air_datas[@intFromEnum(inst)].bin_op;
                 const lhs_scalar_ty = f.typeOf(bin_op.lhs).scalarType(zcu);
                 // For binary operations @TypeOf(lhs)==@TypeOf(rhs),
                 // so we only check one.
                 break :blk if (lhs_scalar_ty.isInt(zcu))
                     try airBinOp(f, inst, "%", "rem", .none)
                 else
-                    try airBinFloatOp(f, inst, "fmod");
+                    try airBinBuiltinCall(f, inst, "fmod", .none);
             },
             .div_floor => try airBinBuiltinCall(f, inst, "div_floor", .none),
             .mod       => try airBinBuiltinCall(f, inst, "mod", .none),
-            .abs       => try airAbs(f, inst),
+            .abs       => try airUnBuiltinCall(f, inst, air_datas[@intFromEnum(inst)].ty_op.operand, "abs", .none),
 
             .add_wrap => try airBinBuiltinCall(f, inst, "addw", .bits),
             .sub_wrap => try airBinBuiltinCall(f, inst, "subw", .bits),
@@ -3230,19 +3231,19 @@ fn genBodyInner(f: *Function, body: []const Air.Inst.Index) error{ AnalysisFail,
             .mul_sat => try airBinBuiltinCall(f, inst, "muls", .bits),
             .shl_sat => try airBinBuiltinCall(f, inst, "shls", .bits),
 
-            .sqrt        => try airUnFloatOp(f, inst, "sqrt"),
-            .sin         => try airUnFloatOp(f, inst, "sin"),
-            .cos         => try airUnFloatOp(f, inst, "cos"),
-            .tan         => try airUnFloatOp(f, inst, "tan"),
-            .exp         => try airUnFloatOp(f, inst, "exp"),
-            .exp2        => try airUnFloatOp(f, inst, "exp2"),
-            .log         => try airUnFloatOp(f, inst, "log"),
-            .log2        => try airUnFloatOp(f, inst, "log2"),
-            .log10       => try airUnFloatOp(f, inst, "log10"),
-            .floor       => try airUnFloatOp(f, inst, "floor"),
-            .ceil        => try airUnFloatOp(f, inst, "ceil"),
-            .round       => try airUnFloatOp(f, inst, "round"),
-            .trunc_float => try airUnFloatOp(f, inst, "trunc"),
+            .sqrt        => try airUnBuiltinCall(f, inst, air_datas[@intFromEnum(inst)].un_op, "sqrt", .none),
+            .sin         => try airUnBuiltinCall(f, inst, air_datas[@intFromEnum(inst)].un_op, "sin", .none),
+            .cos         => try airUnBuiltinCall(f, inst, air_datas[@intFromEnum(inst)].un_op, "cos", .none),
+            .tan         => try airUnBuiltinCall(f, inst, air_datas[@intFromEnum(inst)].un_op, "tan", .none),
+            .exp         => try airUnBuiltinCall(f, inst, air_datas[@intFromEnum(inst)].un_op, "exp", .none),
+            .exp2        => try airUnBuiltinCall(f, inst, air_datas[@intFromEnum(inst)].un_op, "exp2", .none),
+            .log         => try airUnBuiltinCall(f, inst, air_datas[@intFromEnum(inst)].un_op, "log", .none),
+            .log2        => try airUnBuiltinCall(f, inst, air_datas[@intFromEnum(inst)].un_op, "log2", .none),
+            .log10       => try airUnBuiltinCall(f, inst, air_datas[@intFromEnum(inst)].un_op, "log10", .none),
+            .floor       => try airUnBuiltinCall(f, inst, air_datas[@intFromEnum(inst)].un_op, "floor", .none),
+            .ceil        => try airUnBuiltinCall(f, inst, air_datas[@intFromEnum(inst)].un_op, "ceil", .none),
+            .round       => try airUnBuiltinCall(f, inst, air_datas[@intFromEnum(inst)].un_op, "round", .none),
+            .trunc_float => try airUnBuiltinCall(f, inst, air_datas[@intFromEnum(inst)].un_op, "trunc", .none),
 
             .mul_add => try airMulAdd(f, inst),
 
@@ -3251,21 +3252,21 @@ fn genBodyInner(f: *Function, body: []const Air.Inst.Index) error{ AnalysisFail,
             .mul_with_overflow => try airOverflow(f, inst, "mul", .bits),
             .shl_with_overflow => try airOverflow(f, inst, "shl", .bits),
 
-            .min => try airMinMax(f, inst, '<', "fmin"),
-            .max => try airMinMax(f, inst, '>', "fmax"),
+            .min => try airMinMax(f, inst, '<', "min"),
+            .max => try airMinMax(f, inst, '>', "max"),
 
             .slice => try airSlice(f, inst),
 
-            .cmp_gt  => try airCmpOp(f, inst, f.air.instructions.items(.data)[@intFromEnum(inst)].bin_op, .gt),
-            .cmp_gte => try airCmpOp(f, inst, f.air.instructions.items(.data)[@intFromEnum(inst)].bin_op, .gte),
-            .cmp_lt  => try airCmpOp(f, inst, f.air.instructions.items(.data)[@intFromEnum(inst)].bin_op, .lt),
-            .cmp_lte => try airCmpOp(f, inst, f.air.instructions.items(.data)[@intFromEnum(inst)].bin_op, .lte),
+            .cmp_gt  => try airCmpOp(f, inst, air_datas[@intFromEnum(inst)].bin_op, .gt),
+            .cmp_gte => try airCmpOp(f, inst, air_datas[@intFromEnum(inst)].bin_op, .gte),
+            .cmp_lt  => try airCmpOp(f, inst, air_datas[@intFromEnum(inst)].bin_op, .lt),
+            .cmp_lte => try airCmpOp(f, inst, air_datas[@intFromEnum(inst)].bin_op, .lte),
 
             .cmp_eq  => try airEquality(f, inst, .eq),
             .cmp_neq => try airEquality(f, inst, .neq),
 
             .cmp_vector => blk: {
-                const ty_pl = f.air.instructions.items(.data)[@intFromEnum(inst)].ty_pl;
+                const ty_pl = air_datas[@intFromEnum(inst)].ty_pl;
                 const extra = f.air.extraData(Air.VectorCmp, ty_pl.payload).data;
                 break :blk try airCmpOp(f, inst, extra, extra.compareOperator());
             },
@@ -3324,11 +3325,11 @@ fn genBodyInner(f: *Function, body: []const Air.Inst.Index) error{ AnalysisFail,
             .memcpy           => try airMemcpy(f, inst),
             .set_union_tag    => try airSetUnionTag(f, inst),
             .get_union_tag    => try airGetUnionTag(f, inst),
-            .clz              => try airUnBuiltinCall(f, inst, "clz", .bits),
-            .ctz              => try airUnBuiltinCall(f, inst, "ctz", .bits),
-            .popcount         => try airUnBuiltinCall(f, inst, "popcount", .bits),
-            .byte_swap        => try airUnBuiltinCall(f, inst, "byte_swap", .bits),
-            .bit_reverse      => try airUnBuiltinCall(f, inst, "bit_reverse", .bits),
+            .clz              => try airUnBuiltinCall(f, inst, air_datas[@intFromEnum(inst)].ty_op.operand, "clz", .bits),
+            .ctz              => try airUnBuiltinCall(f, inst, air_datas[@intFromEnum(inst)].ty_op.operand, "ctz", .bits),
+            .popcount         => try airUnBuiltinCall(f, inst, air_datas[@intFromEnum(inst)].ty_op.operand, "popcount", .bits),
+            .byte_swap        => try airUnBuiltinCall(f, inst, air_datas[@intFromEnum(inst)].ty_op.operand, "byte_swap", .bits),
+            .bit_reverse      => try airUnBuiltinCall(f, inst, air_datas[@intFromEnum(inst)].ty_op.operand, "bit_reverse", .bits),
             .tag_name         => try airTagName(f, inst),
             .error_name       => try airErrorName(f, inst),
             .splat            => try airSplat(f, inst),
@@ -4139,7 +4140,7 @@ fn airNot(f: *Function, inst: Air.Inst.Index) !CValue {
     const ty_op = f.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
     const operand_ty = f.typeOf(ty_op.operand);
     const scalar_ty = operand_ty.scalarType(zcu);
-    if (scalar_ty.toIntern() != .bool_type) return try airUnBuiltinCall(f, inst, "not", .bits);
+    if (scalar_ty.toIntern() != .bool_type) return try airUnBuiltinCall(f, inst, ty_op.operand, "not", .bits);
 
     const op = try f.resolveInst(ty_op.operand);
     try reap(f, inst, &.{ty_op.operand});
@@ -4389,10 +4390,8 @@ fn airMinMax(f: *Function, inst: Air.Inst.Index, operator: u8, operation: []cons
     const inst_ty = f.typeOfIndex(inst);
     const inst_scalar_ty = inst_ty.scalarType(zcu);
 
-    if (inst_scalar_ty.isInt(zcu) and inst_scalar_ty.bitSize(zcu) > 64)
-        return try airBinBuiltinCall(f, inst, operation[1..], .none);
-    if (inst_scalar_ty.isRuntimeFloat())
-        return try airBinFloatOp(f, inst, operation);
+    if ((inst_scalar_ty.isInt(zcu) and inst_scalar_ty.bitSize(zcu) > 64) or inst_scalar_ty.isRuntimeFloat())
+        return try airBinBuiltinCall(f, inst, operation, .none);
 
     const lhs = try f.resolveInst(bin_op.lhs);
     const rhs = try f.resolveInst(bin_op.rhs);
@@ -6276,17 +6275,17 @@ fn airIntFromPtr(f: *Function, inst: Air.Inst.Index) !CValue {
 fn airUnBuiltinCall(
     f: *Function,
     inst: Air.Inst.Index,
+    operand_ref: Air.Inst.Ref,
     operation: []const u8,
     info: BuiltinInfo,
 ) !CValue {
     const zcu = f.object.dg.zcu;
-    const ty_op = f.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
 
-    const operand = try f.resolveInst(ty_op.operand);
-    try reap(f, inst, &.{ty_op.operand});
+    const operand = try f.resolveInst(operand_ref);
+    try reap(f, inst, &.{operand_ref});
     const inst_ty = f.typeOfIndex(inst);
     const inst_scalar_ty = inst_ty.scalarType(zcu);
-    const operand_ty = f.typeOf(ty_op.operand);
+    const operand_ty = f.typeOf(operand_ref);
     const scalar_ty = operand_ty.scalarType(zcu);
 
     const inst_scalar_ctype = try f.ctypeFromType(inst_scalar_ty, .complete);
@@ -6799,11 +6798,27 @@ fn airMemcpy(f: *Function, inst: Air.Inst.Index) !CValue {
     const src_ty = f.typeOf(bin_op.rhs);
     const writer = f.object.writer();
 
+    if (dest_ty.ptrSize(zcu) != .One) {
+        try writer.writeAll("if (");
+        try writeArrayLen(f, writer, dest_ptr, dest_ty);
+        try writer.writeAll(" != 0) ");
+    }
     try writer.writeAll("memcpy(");
     try writeSliceOrPtr(f, writer, dest_ptr, dest_ty);
     try writer.writeAll(", ");
     try writeSliceOrPtr(f, writer, src_ptr, src_ty);
     try writer.writeAll(", ");
+    try writeArrayLen(f, writer, dest_ptr, dest_ty);
+    try writer.writeAll(" * sizeof(");
+    try f.renderType(writer, dest_ty.elemType2(zcu));
+    try writer.writeAll("));\n");
+
+    try reap(f, inst, &.{ bin_op.lhs, bin_op.rhs });
+    return .none;
+}
+
+fn writeArrayLen(f: *Function, writer: ArrayListWriter, dest_ptr: CValue, dest_ty: Type) !void {
+    const zcu = f.object.dg.zcu;
     switch (dest_ty.ptrSize(zcu)) {
         .One => try writer.print("{}", .{
             try f.fmtIntLiteral(try zcu.intValue(Type.usize, dest_ty.childType(zcu).arrayLen(zcu))),
@@ -6811,12 +6826,6 @@ fn airMemcpy(f: *Function, inst: Air.Inst.Index) !CValue {
         .Many, .C => unreachable,
         .Slice => try f.writeCValueMember(writer, dest_ptr, .{ .identifier = "len" }),
     }
-    try writer.writeAll(" * sizeof(");
-    try f.renderType(writer, dest_ty.elemType2(zcu));
-    try writer.writeAll("));\n");
-
-    try reap(f, inst, &.{ bin_op.lhs, bin_op.rhs });
-    return .none;
 }
 
 fn airSetUnionTag(f: *Function, inst: Air.Inst.Index) !CValue {
@@ -6999,7 +7008,6 @@ fn airReduce(f: *Function, inst: Air.Inst.Index) !CValue {
     const use_operator = scalar_ty.bitSize(zcu) <= 64;
     const op: union(enum) {
         const Func = struct { operation: []const u8, info: BuiltinInfo = .none };
-        float_op: Func,
         builtin: Func,
         infix: []const u8,
         ternary: []const u8,
@@ -7008,30 +7016,22 @@ fn airReduce(f: *Function, inst: Air.Inst.Index) !CValue {
         .Or => if (use_operator) .{ .infix = " |= " } else .{ .builtin = .{ .operation = "or" } },
         .Xor => if (use_operator) .{ .infix = " ^= " } else .{ .builtin = .{ .operation = "xor" } },
         .Min => switch (scalar_ty.zigTypeTag(zcu)) {
-            .Int => if (use_operator) .{ .ternary = " < " } else .{
-                .builtin = .{ .operation = "min" },
-            },
-            .Float => .{ .float_op = .{ .operation = "fmin" } },
+            .Int => if (use_operator) .{ .ternary = " < " } else .{ .builtin = .{ .operation = "min" } },
+            .Float => .{ .builtin = .{ .operation = "min" } },
             else => unreachable,
         },
         .Max => switch (scalar_ty.zigTypeTag(zcu)) {
-            .Int => if (use_operator) .{ .ternary = " > " } else .{
-                .builtin = .{ .operation = "max" },
-            },
-            .Float => .{ .float_op = .{ .operation = "fmax" } },
+            .Int => if (use_operator) .{ .ternary = " > " } else .{ .builtin = .{ .operation = "max" } },
+            .Float => .{ .builtin = .{ .operation = "max" } },
             else => unreachable,
         },
         .Add => switch (scalar_ty.zigTypeTag(zcu)) {
-            .Int => if (use_operator) .{ .infix = " += " } else .{
-                .builtin = .{ .operation = "addw", .info = .bits },
-            },
+            .Int => if (use_operator) .{ .infix = " += " } else .{ .builtin = .{ .operation = "addw", .info = .bits } },
             .Float => .{ .builtin = .{ .operation = "add" } },
             else => unreachable,
         },
         .Mul => switch (scalar_ty.zigTypeTag(zcu)) {
-            .Int => if (use_operator) .{ .infix = " *= " } else .{
-                .builtin = .{ .operation = "mulw", .info = .bits },
-            },
+            .Int => if (use_operator) .{ .infix = " *= " } else .{ .builtin = .{ .operation = "mulw", .info = .bits } },
             .Float => .{ .builtin = .{ .operation = "mul" } },
             else => unreachable,
         },
@@ -7095,17 +7095,6 @@ fn airReduce(f: *Function, inst: Air.Inst.Index) !CValue {
     const v = try Vectorize.start(f, inst, writer, operand_ty);
     try f.writeCValue(writer, accum, .Other);
     switch (op) {
-        .float_op => |func| {
-            try writer.writeAll(" = zig_float_fn_");
-            try f.object.dg.renderTypeForBuiltinFnName(writer, scalar_ty);
-            try writer.print("_{s}(", .{func.operation});
-            try f.writeCValue(writer, accum, .FunctionArgument);
-            try writer.writeAll(", ");
-            try f.writeCValue(writer, operand, .Other);
-            try v.elem(f, writer);
-            try f.object.dg.renderBuiltinInfo(writer, scalar_ty, func.info);
-            try writer.writeByte(')');
-        },
         .builtin => |func| {
             try writer.print(" = zig_{s}_", .{func.operation});
             try f.object.dg.renderTypeForBuiltinFnName(writer, scalar_ty);
@@ -7386,110 +7375,6 @@ fn airWasmMemoryGrow(f: *Function, inst: Air.Inst.Index) !CValue {
     return local;
 }
 
-fn airFloatNeg(f: *Function, inst: Air.Inst.Index) !CValue {
-    const zcu = f.object.dg.zcu;
-    const un_op = f.air.instructions.items(.data)[@intFromEnum(inst)].un_op;
-
-    const operand = try f.resolveInst(un_op);
-    try reap(f, inst, &.{un_op});
-
-    const operand_ty = f.typeOf(un_op);
-    const scalar_ty = operand_ty.scalarType(zcu);
-
-    const writer = f.object.writer();
-    const local = try f.allocLocal(inst, operand_ty);
-    const v = try Vectorize.start(f, inst, writer, operand_ty);
-    try f.writeCValue(writer, local, .Other);
-    try v.elem(f, writer);
-    try writer.writeAll(" = zig_neg_");
-    try f.object.dg.renderTypeForBuiltinFnName(writer, scalar_ty);
-    try writer.writeByte('(');
-    try f.writeCValue(writer, operand, .FunctionArgument);
-    try v.elem(f, writer);
-    try writer.writeAll(");\n");
-    try v.end(f, inst, writer);
-
-    return local;
-}
-
-fn airAbs(f: *Function, inst: Air.Inst.Index) !CValue {
-    const zcu = f.object.dg.zcu;
-    const ty_op = f.air.instructions.items(.data)[@intFromEnum(inst)].ty_op;
-    const operand = try f.resolveInst(ty_op.operand);
-    const ty = f.typeOf(ty_op.operand);
-    const scalar_ty = ty.scalarType(zcu);
-
-    switch (scalar_ty.zigTypeTag(zcu)) {
-        .Int => if (ty.zigTypeTag(zcu) == .Vector) {
-            return f.fail("TODO implement airAbs for '{}'", .{ty.fmt(zcu)});
-        } else {
-            return airUnBuiltinCall(f, inst, "abs", .none);
-        },
-        .Float => return unFloatOp(f, inst, operand, ty, "fabs"),
-        else => unreachable,
-    }
-}
-
-fn unFloatOp(f: *Function, inst: Air.Inst.Index, operand: CValue, ty: Type, operation: []const u8) !CValue {
-    const zcu = f.object.dg.zcu;
-    const scalar_ty = ty.scalarType(zcu);
-
-    const writer = f.object.writer();
-    const local = try f.allocLocal(inst, ty);
-    const v = try Vectorize.start(f, inst, writer, ty);
-    try f.writeCValue(writer, local, .Other);
-    try v.elem(f, writer);
-    try writer.writeAll(" = zig_float_fn_");
-    try f.object.dg.renderTypeForBuiltinFnName(writer, scalar_ty);
-    try writer.print("_{s}(", .{operation});
-    try f.writeCValue(writer, operand, .FunctionArgument);
-    try v.elem(f, writer);
-    try writer.writeAll(");\n");
-    try v.end(f, inst, writer);
-
-    return local;
-}
-
-fn airUnFloatOp(f: *Function, inst: Air.Inst.Index, operation: []const u8) !CValue {
-    const un_op = f.air.instructions.items(.data)[@intFromEnum(inst)].un_op;
-
-    const operand = try f.resolveInst(un_op);
-    try reap(f, inst, &.{un_op});
-
-    const inst_ty = f.typeOfIndex(inst);
-    return unFloatOp(f, inst, operand, inst_ty, operation);
-}
-
-fn airBinFloatOp(f: *Function, inst: Air.Inst.Index, operation: []const u8) !CValue {
-    const zcu = f.object.dg.zcu;
-    const bin_op = f.air.instructions.items(.data)[@intFromEnum(inst)].bin_op;
-
-    const lhs = try f.resolveInst(bin_op.lhs);
-    const rhs = try f.resolveInst(bin_op.rhs);
-    try reap(f, inst, &.{ bin_op.lhs, bin_op.rhs });
-
-    const inst_ty = f.typeOfIndex(inst);
-    const inst_scalar_ty = inst_ty.scalarType(zcu);
-
-    const writer = f.object.writer();
-    const local = try f.allocLocal(inst, inst_ty);
-    const v = try Vectorize.start(f, inst, writer, inst_ty);
-    try f.writeCValue(writer, local, .Other);
-    try v.elem(f, writer);
-    try writer.writeAll(" = zig_float_fn_");
-    try f.object.dg.renderTypeForBuiltinFnName(writer, inst_scalar_ty);
-    try writer.print("_{s}(", .{operation});
-    try f.writeCValue(writer, lhs, .FunctionArgument);
-    try v.elem(f, writer);
-    try writer.writeAll(", ");
-    try f.writeCValue(writer, rhs, .FunctionArgument);
-    try v.elem(f, writer);
-    try writer.writeAll(");\n");
-    try v.end(f, inst, writer);
-
-    return local;
-}
-
 fn airMulAdd(f: *Function, inst: Air.Inst.Index) !CValue {
     const zcu = f.object.dg.zcu;
     const pl_op = f.air.instructions.items(.data)[@intFromEnum(inst)].pl_op;
@@ -7508,9 +7393,9 @@ fn airMulAdd(f: *Function, inst: Air.Inst.Index) !CValue {
     const v = try Vectorize.start(f, inst, writer, inst_ty);
     try f.writeCValue(writer, local, .Other);
     try v.elem(f, writer);
-    try writer.writeAll(" = zig_float_fn_");
+    try writer.writeAll(" = zig_fma_");
     try f.object.dg.renderTypeForBuiltinFnName(writer, inst_scalar_ty);
-    try writer.writeAll("_fma(");
+    try writer.writeByte('(');
     try f.writeCValue(writer, mulend1, .FunctionArgument);
     try v.elem(f, writer);
     try writer.writeAll(", ");
diff --git a/src/codegen/c/Type.zig b/src/codegen/c/Type.zig
index 357677522c..e6a9dc69a3 100644
--- a/src/codegen/c/Type.zig
+++ b/src/codegen/c/Type.zig
@@ -1468,7 +1468,6 @@ pub const Pool = struct {
             .bool_false,
             .empty_struct,
             .generic_poison,
-            .var_args_param_type,
             .none,
             => unreachable,
 
@@ -1858,7 +1857,7 @@ pub const Pool = struct {
                                     loaded_tag.names.get(ip)[field_index].toSlice(ip),
                                 );
                                 const field_alignas = AlignAs.fromAlignment(.{
-                                    .@"align" = loaded_union.fieldAlign(ip, @intCast(field_index)),
+                                    .@"align" = loaded_union.fieldAlign(ip, field_index),
                                     .abi = field_type.abiAlignment(zcu),
                                 });
                                 pool.addHashedExtraAssumeCapacityTo(scratch, &hasher, Field, .{
diff --git a/src/codegen/llvm.zig b/src/codegen/llvm.zig
index f8fce85c80..c904fc42c1 100644
--- a/src/codegen/llvm.zig
+++ b/src/codegen/llvm.zig
@@ -1384,7 +1384,7 @@ pub const Object = struct {
         const namespace = zcu.namespacePtr(decl.src_namespace);
         const owner_mod = namespace.file_scope.mod;
         const fn_info = zcu.typeToFunc(decl.typeOf(zcu)).?;
-        const target = zcu.getTarget();
+        const target = owner_mod.resolved_target.result;
         const ip = &zcu.intern_pool;
 
         var dg: DeclGen = .{
@@ -1456,7 +1456,7 @@ pub const Object = struct {
         var llvm_arg_i: u32 = 0;
 
         // This gets the LLVM values from the function and stores them in `dg.args`.
-        const sret = firstParamSRet(fn_info, zcu);
+        const sret = firstParamSRet(fn_info, zcu, target);
         const ret_ptr: Builder.Value = if (sret) param: {
             const param = wip.arg(llvm_arg_i);
             llvm_arg_i += 1;
@@ -2755,7 +2755,7 @@ pub const Object = struct {
 
                 // Return type goes first.
                 if (Type.fromInterned(fn_info.return_type).hasRuntimeBitsIgnoreComptime(mod)) {
-                    const sret = firstParamSRet(fn_info, mod);
+                    const sret = firstParamSRet(fn_info, mod, target);
                     const ret_ty = if (sret) Type.void else Type.fromInterned(fn_info.return_type);
                     debug_param_types.appendAssumeCapacity(try o.lowerDebugType(ret_ty));
 
@@ -2881,7 +2881,7 @@ pub const Object = struct {
         assert(decl.has_tv);
         const fn_info = zcu.typeToFunc(zig_fn_type).?;
         const target = owner_mod.resolved_target.result;
-        const sret = firstParamSRet(fn_info, zcu);
+        const sret = firstParamSRet(fn_info, zcu, target);
 
         const is_extern = decl.isExtern(zcu);
         const function_index = try o.builder.addFunction(
@@ -3235,7 +3235,6 @@ pub const Object = struct {
             .bool_false,
             .empty_struct,
             .generic_poison,
-            .var_args_param_type,
             .none,
             => unreachable,
             else => switch (ip.indexToKey(t.toIntern())) {
@@ -3604,7 +3603,7 @@ pub const Object = struct {
         var llvm_params = std.ArrayListUnmanaged(Builder.Type){};
         defer llvm_params.deinit(o.gpa);
 
-        if (firstParamSRet(fn_info, mod)) {
+        if (firstParamSRet(fn_info, mod, target)) {
             try llvm_params.append(o.gpa, .ptr);
         }
 
@@ -4434,6 +4433,10 @@ pub const Object = struct {
             if (!param_ty.isPtrLikeOptional(mod) and !ptr_info.flags.is_allowzero) {
                 try attributes.addParamAttr(llvm_arg_i, .nonnull, &o.builder);
             }
+            if (fn_info.cc == .Interrupt) {
+                const child_type = try lowerType(o, Type.fromInterned(ptr_info.child));
+                try attributes.addParamAttr(llvm_arg_i, .{ .byval = child_type }, &o.builder);
+            }
             if (ptr_info.flags.is_const) {
                 try attributes.addParamAttr(llvm_arg_i, .readonly, &o.builder);
             }
@@ -4646,8 +4649,8 @@ pub const DeclGen = struct {
                 debug_global_var,
                 debug_expression,
             );
-            if (!is_internal_linkage or decl.isExtern(zcu))
-                variable_index.setGlobalVariableExpression(debug_global_var_expression, &o.builder);
+
+            variable_index.setGlobalVariableExpression(debug_global_var_expression, &o.builder);
             try o.debug_globals.append(o.gpa, debug_global_var_expression);
         }
     }
@@ -5130,7 +5133,7 @@ pub const FuncGen = struct {
         const return_type = Type.fromInterned(fn_info.return_type);
         const llvm_fn = try self.resolveInst(pl_op.operand);
         const target = mod.getTarget();
-        const sret = firstParamSRet(fn_info, mod);
+        const sret = firstParamSRet(fn_info, mod, target);
 
         var llvm_args = std.ArrayList(Builder.Value).init(self.gpa);
         defer llvm_args.deinit();
@@ -7496,7 +7499,8 @@ pub const FuncGen = struct {
         const o = self.dg.object;
         const pl_op = self.air.instructions.items(.data)[@intFromEnum(inst)].pl_op;
         const index = pl_op.payload;
-        return self.wip.callIntrinsic(.normal, .none, .@"wasm.memory.size", &.{.i32}, &.{
+        const llvm_usize = try o.lowerType(Type.usize);
+        return self.wip.callIntrinsic(.normal, .none, .@"wasm.memory.size", &.{llvm_usize}, &.{
             try o.builder.intValue(.i32, index),
         }, "");
     }
@@ -7505,7 +7509,8 @@ pub const FuncGen = struct {
         const o = self.dg.object;
         const pl_op = self.air.instructions.items(.data)[@intFromEnum(inst)].pl_op;
         const index = pl_op.payload;
-        return self.wip.callIntrinsic(.normal, .none, .@"wasm.memory.grow", &.{.i32}, &.{
+        const llvm_isize = try o.lowerType(Type.isize);
+        return self.wip.callIntrinsic(.normal, .none, .@"wasm.memory.grow", &.{llvm_isize}, &.{
             try o.builder.intValue(.i32, index), try self.resolveInst(pl_op.operand),
         }, "");
     }
@@ -9993,20 +9998,21 @@ pub const FuncGen = struct {
             return self.wip.conv(.unsigned, small_int_val, int_llvm_ty, "");
         }
 
-        const tag_int = blk: {
+        const tag_int_val = blk: {
             const tag_ty = union_ty.unionTagTypeHypothetical(mod);
             const union_field_name = union_obj.loadTagType(ip).names.get(ip)[extra.field_index];
             const enum_field_index = tag_ty.enumFieldIndex(union_field_name, mod).?;
             const tag_val = try mod.enumValueFieldIndex(tag_ty, enum_field_index);
-            const tag_int_val = try tag_val.intFromEnum(tag_ty, mod);
-            break :blk tag_int_val.toUnsignedInt(mod);
+            break :blk try tag_val.intFromEnum(tag_ty, mod);
         };
         if (layout.payload_size == 0) {
             if (layout.tag_size == 0) {
                 return .none;
             }
             assert(!isByRef(union_ty, mod));
-            return o.builder.intValue(union_llvm_ty, tag_int);
+            var big_int_space: Value.BigIntSpace = undefined;
+            const tag_big_int = tag_int_val.toBigInt(&big_int_space, mod);
+            return try o.builder.bigIntValue(union_llvm_ty, tag_big_int);
         }
         assert(isByRef(union_ty, mod));
         // The llvm type of the alloca will be the named LLVM union type, and will not
@@ -10080,7 +10086,9 @@ pub const FuncGen = struct {
             const indices: [2]Builder.Value = .{ usize_zero, try o.builder.intValue(.i32, tag_index) };
             const field_ptr = try self.wip.gep(.inbounds, llvm_union_ty, result_ptr, &indices, "");
             const tag_ty = try o.lowerType(Type.fromInterned(union_obj.enum_tag_ty));
-            const llvm_tag = try o.builder.intValue(tag_ty, tag_int);
+            var big_int_space: Value.BigIntSpace = undefined;
+            const tag_big_int = tag_int_val.toBigInt(&big_int_space, mod);
+            const llvm_tag = try o.builder.bigIntValue(tag_ty, tag_big_int);
             const tag_alignment = Type.fromInterned(union_obj.enum_tag_ty).abiAlignment(mod).toLlvm();
             _ = try self.wip.store(.normal, llvm_tag, field_ptr, tag_alignment);
         }
@@ -10865,38 +10873,38 @@ fn toLlvmGlobalAddressSpace(wanted_address_space: std.builtin.AddressSpace, targ
     };
 }
 
-fn firstParamSRet(fn_info: InternPool.Key.FuncType, mod: *Module) bool {
+fn firstParamSRet(fn_info: InternPool.Key.FuncType, zcu: *Zcu, target: std.Target) bool {
     const return_type = Type.fromInterned(fn_info.return_type);
-    if (!return_type.hasRuntimeBitsIgnoreComptime(mod)) return false;
+    if (!return_type.hasRuntimeBitsIgnoreComptime(zcu)) return false;
 
-    const target = mod.getTarget();
-    switch (fn_info.cc) {
-        .Unspecified, .Inline => return isByRef(return_type, mod),
+    return switch (fn_info.cc) {
+        .Unspecified, .Inline => isByRef(return_type, zcu),
         .C => switch (target.cpu.arch) {
-            .mips, .mipsel => return false,
+            .mips, .mipsel => false,
+            .x86 => isByRef(return_type, zcu),
             .x86_64 => switch (target.os.tag) {
-                .windows => return x86_64_abi.classifyWindows(return_type, mod) == .memory,
-                else => return firstParamSRetSystemV(return_type, mod),
+                .windows => x86_64_abi.classifyWindows(return_type, zcu) == .memory,
+                else => firstParamSRetSystemV(return_type, zcu, target),
             },
-            .wasm32 => return wasm_c_abi.classifyType(return_type, mod)[0] == .indirect,
-            .aarch64, .aarch64_be => return aarch64_c_abi.classifyType(return_type, mod) == .memory,
-            .arm, .armeb => switch (arm_c_abi.classifyType(return_type, mod, .ret)) {
-                .memory, .i64_array => return true,
-                .i32_array => |size| return size != 1,
-                .byval => return false,
+            .wasm32 => wasm_c_abi.classifyType(return_type, zcu)[0] == .indirect,
+            .aarch64, .aarch64_be => aarch64_c_abi.classifyType(return_type, zcu) == .memory,
+            .arm, .armeb => switch (arm_c_abi.classifyType(return_type, zcu, .ret)) {
+                .memory, .i64_array => true,
+                .i32_array => |size| size != 1,
+                .byval => false,
             },
-            .riscv32, .riscv64 => return riscv_c_abi.classifyType(return_type, mod) == .memory,
-            else => return false, // TODO investigate C ABI for other architectures
+            .riscv32, .riscv64 => riscv_c_abi.classifyType(return_type, zcu) == .memory,
+            else => false, // TODO investigate C ABI for other architectures
         },
-        .SysV => return firstParamSRetSystemV(return_type, mod),
-        .Win64 => return x86_64_abi.classifyWindows(return_type, mod) == .memory,
-        .Stdcall => return !isScalar(mod, return_type),
-        else => return false,
-    }
+        .SysV => firstParamSRetSystemV(return_type, zcu, target),
+        .Win64 => x86_64_abi.classifyWindows(return_type, zcu) == .memory,
+        .Stdcall => !isScalar(zcu, return_type),
+        else => false,
+    };
 }
 
-fn firstParamSRetSystemV(ty: Type, mod: *Module) bool {
-    const class = x86_64_abi.classifySystemV(ty, mod, .ret);
+fn firstParamSRetSystemV(ty: Type, zcu: *Zcu, target: std.Target) bool {
+    const class = x86_64_abi.classifySystemV(ty, zcu, target, .ret);
     if (class[0] == .memory) return true;
     if (class[0] == .x87 and class[2] != .none) return true;
     return false;
@@ -10922,6 +10930,7 @@ fn lowerFnRetTy(o: *Object, fn_info: InternPool.Key.FuncType) Allocator.Error!Bu
         .C => {
             switch (target.cpu.arch) {
                 .mips, .mipsel => return o.lowerType(return_type),
+                .x86 => return if (isByRef(return_type, mod)) .void else o.lowerType(return_type),
                 .x86_64 => switch (target.os.tag) {
                     .windows => return lowerWin64FnRetTy(o, fn_info),
                     else => return lowerSystemVFnRetTy(o, fn_info),
@@ -11014,7 +11023,8 @@ fn lowerSystemVFnRetTy(o: *Object, fn_info: InternPool.Key.FuncType) Allocator.E
     if (isScalar(mod, return_type)) {
         return o.lowerType(return_type);
     }
-    const classes = x86_64_abi.classifySystemV(return_type, mod, .ret);
+    const target = mod.getTarget();
+    const classes = x86_64_abi.classifySystemV(return_type, mod, target, .ret);
     if (classes[0] == .memory) return .void;
     var types_index: u32 = 0;
     var types_buffer: [8]Builder.Type = undefined;
@@ -11098,8 +11108,8 @@ const ParamTypeIterator = struct {
 
     pub fn next(it: *ParamTypeIterator) Allocator.Error!?Lowering {
         if (it.zig_index >= it.fn_info.param_types.len) return null;
-        const mod = it.object.module;
-        const ip = &mod.intern_pool;
+        const zcu = it.object.module;
+        const ip = &zcu.intern_pool;
         const ty = it.fn_info.param_types.get(ip)[it.zig_index];
         it.byval_attr = false;
         return nextInner(it, Type.fromInterned(ty));
@@ -11107,8 +11117,8 @@ const ParamTypeIterator = struct {
 
     /// `airCall` uses this instead of `next` so that it can take into account variadic functions.
     pub fn nextCall(it: *ParamTypeIterator, fg: *FuncGen, args: []const Air.Inst.Ref) Allocator.Error!?Lowering {
-        const mod = it.object.module;
-        const ip = &mod.intern_pool;
+        const zcu = it.object.module;
+        const ip = &zcu.intern_pool;
         if (it.zig_index >= it.fn_info.param_types.len) {
             if (it.zig_index >= args.len) {
                 return null;
@@ -11121,10 +11131,10 @@ const ParamTypeIterator = struct {
     }
 
     fn nextInner(it: *ParamTypeIterator, ty: Type) Allocator.Error!?Lowering {
-        const mod = it.object.module;
-        const target = mod.getTarget();
+        const zcu = it.object.module;
+        const target = zcu.getTarget();
 
-        if (!ty.hasRuntimeBitsIgnoreComptime(mod)) {
+        if (!ty.hasRuntimeBitsIgnoreComptime(zcu)) {
             it.zig_index += 1;
             return .no_bits;
         }
@@ -11132,12 +11142,12 @@ const ParamTypeIterator = struct {
             .Unspecified, .Inline => {
                 it.zig_index += 1;
                 it.llvm_index += 1;
-                if (ty.isSlice(mod) or
-                    (ty.zigTypeTag(mod) == .Optional and ty.optionalChild(mod).isSlice(mod) and !ty.ptrAllowsZero(mod)))
+                if (ty.isSlice(zcu) or
+                    (ty.zigTypeTag(zcu) == .Optional and ty.optionalChild(zcu).isSlice(zcu) and !ty.ptrAllowsZero(zcu)))
                 {
                     it.llvm_index += 1;
                     return .slice;
-                } else if (isByRef(ty, mod)) {
+                } else if (isByRef(ty, zcu)) {
                     return .byref;
                 } else {
                     return .byval;
@@ -11146,87 +11156,85 @@ const ParamTypeIterator = struct {
             .Async => {
                 @panic("TODO implement async function lowering in the LLVM backend");
             },
-            .C => {
-                switch (target.cpu.arch) {
-                    .mips, .mipsel => {
-                        it.zig_index += 1;
-                        it.llvm_index += 1;
+            .C => switch (target.cpu.arch) {
+                .mips, .mipsel => {
+                    it.zig_index += 1;
+                    it.llvm_index += 1;
+                    return .byval;
+                },
+                .x86_64 => switch (target.os.tag) {
+                    .windows => return it.nextWin64(ty),
+                    else => return it.nextSystemV(ty),
+                },
+                .wasm32 => {
+                    it.zig_index += 1;
+                    it.llvm_index += 1;
+                    if (isScalar(zcu, ty)) {
                         return .byval;
-                    },
-                    .x86_64 => switch (target.os.tag) {
-                        .windows => return it.nextWin64(ty),
-                        else => return it.nextSystemV(ty),
-                    },
-                    .wasm32 => {
-                        it.zig_index += 1;
-                        it.llvm_index += 1;
-                        if (isScalar(mod, ty)) {
-                            return .byval;
-                        }
-                        const classes = wasm_c_abi.classifyType(ty, mod);
-                        if (classes[0] == .indirect) {
+                    }
+                    const classes = wasm_c_abi.classifyType(ty, zcu);
+                    if (classes[0] == .indirect) {
+                        return .byref;
+                    }
+                    return .abi_sized_int;
+                },
+                .aarch64, .aarch64_be => {
+                    it.zig_index += 1;
+                    it.llvm_index += 1;
+                    switch (aarch64_c_abi.classifyType(ty, zcu)) {
+                        .memory => return .byref_mut,
+                        .float_array => |len| return Lowering{ .float_array = len },
+                        .byval => return .byval,
+                        .integer => {
+                            it.types_len = 1;
+                            it.types_buffer[0] = .i64;
+                            return .multiple_llvm_types;
+                        },
+                        .double_integer => return Lowering{ .i64_array = 2 },
+                    }
+                },
+                .arm, .armeb => {
+                    it.zig_index += 1;
+                    it.llvm_index += 1;
+                    switch (arm_c_abi.classifyType(ty, zcu, .arg)) {
+                        .memory => {
+                            it.byval_attr = true;
                             return .byref;
-                        }
-                        return .abi_sized_int;
-                    },
-                    .aarch64, .aarch64_be => {
-                        it.zig_index += 1;
-                        it.llvm_index += 1;
-                        switch (aarch64_c_abi.classifyType(ty, mod)) {
-                            .memory => return .byref_mut,
-                            .float_array => |len| return Lowering{ .float_array = len },
-                            .byval => return .byval,
-                            .integer => {
-                                it.types_len = 1;
-                                it.types_buffer[0] = .i64;
-                                return .multiple_llvm_types;
-                            },
-                            .double_integer => return Lowering{ .i64_array = 2 },
-                        }
-                    },
-                    .arm, .armeb => {
-                        it.zig_index += 1;
-                        it.llvm_index += 1;
-                        switch (arm_c_abi.classifyType(ty, mod, .arg)) {
-                            .memory => {
-                                it.byval_attr = true;
-                                return .byref;
-                            },
-                            .byval => return .byval,
-                            .i32_array => |size| return Lowering{ .i32_array = size },
-                            .i64_array => |size| return Lowering{ .i64_array = size },
-                        }
-                    },
-                    .riscv32, .riscv64 => {
-                        it.zig_index += 1;
-                        it.llvm_index += 1;
-                        if (ty.toIntern() == .f16_type and
-                            !std.Target.riscv.featureSetHas(target.cpu.features, .d)) return .as_u16;
-                        switch (riscv_c_abi.classifyType(ty, mod)) {
-                            .memory => return .byref_mut,
-                            .byval => return .byval,
-                            .integer => return .abi_sized_int,
-                            .double_integer => return Lowering{ .i64_array = 2 },
-                            .fields => {
-                                it.types_len = 0;
-                                for (0..ty.structFieldCount(mod)) |field_index| {
-                                    const field_ty = ty.structFieldType(field_index, mod);
-                                    if (!field_ty.hasRuntimeBitsIgnoreComptime(mod)) continue;
-                                    it.types_buffer[it.types_len] = try it.object.lowerType(field_ty);
-                                    it.types_len += 1;
-                                }
-                                it.llvm_index += it.types_len - 1;
-                                return .multiple_llvm_types;
-                            },
-                        }
-                    },
-                    // TODO investigate C ABI for other architectures
-                    else => {
-                        it.zig_index += 1;
-                        it.llvm_index += 1;
-                        return .byval;
-                    },
-                }
+                        },
+                        .byval => return .byval,
+                        .i32_array => |size| return Lowering{ .i32_array = size },
+                        .i64_array => |size| return Lowering{ .i64_array = size },
+                    }
+                },
+                .riscv32, .riscv64 => {
+                    it.zig_index += 1;
+                    it.llvm_index += 1;
+                    if (ty.toIntern() == .f16_type and
+                        !std.Target.riscv.featureSetHas(target.cpu.features, .d)) return .as_u16;
+                    switch (riscv_c_abi.classifyType(ty, zcu)) {
+                        .memory => return .byref_mut,
+                        .byval => return .byval,
+                        .integer => return .abi_sized_int,
+                        .double_integer => return Lowering{ .i64_array = 2 },
+                        .fields => {
+                            it.types_len = 0;
+                            for (0..ty.structFieldCount(zcu)) |field_index| {
+                                const field_ty = ty.structFieldType(field_index, zcu);
+                                if (!field_ty.hasRuntimeBitsIgnoreComptime(zcu)) continue;
+                                it.types_buffer[it.types_len] = try it.object.lowerType(field_ty);
+                                it.types_len += 1;
+                            }
+                            it.llvm_index += it.types_len - 1;
+                            return .multiple_llvm_types;
+                        },
+                    }
+                },
+                // TODO investigate C ABI for other architectures
+                else => {
+                    it.zig_index += 1;
+                    it.llvm_index += 1;
+                    return .byval;
+                },
             },
             .Win64 => return it.nextWin64(ty),
             .SysV => return it.nextSystemV(ty),
@@ -11234,7 +11242,7 @@ const ParamTypeIterator = struct {
                 it.zig_index += 1;
                 it.llvm_index += 1;
 
-                if (isScalar(mod, ty)) {
+                if (isScalar(zcu, ty)) {
                     return .byval;
                 } else {
                     it.byval_attr = true;
@@ -11250,10 +11258,10 @@ const ParamTypeIterator = struct {
     }
 
     fn nextWin64(it: *ParamTypeIterator, ty: Type) ?Lowering {
-        const mod = it.object.module;
-        switch (x86_64_abi.classifyWindows(ty, mod)) {
+        const zcu = it.object.module;
+        switch (x86_64_abi.classifyWindows(ty, zcu)) {
             .integer => {
-                if (isScalar(mod, ty)) {
+                if (isScalar(zcu, ty)) {
                     it.zig_index += 1;
                     it.llvm_index += 1;
                     return .byval;
@@ -11283,16 +11291,17 @@ const ParamTypeIterator = struct {
     }
 
     fn nextSystemV(it: *ParamTypeIterator, ty: Type) Allocator.Error!?Lowering {
-        const mod = it.object.module;
-        const ip = &mod.intern_pool;
-        const classes = x86_64_abi.classifySystemV(ty, mod, .arg);
+        const zcu = it.object.module;
+        const ip = &zcu.intern_pool;
+        const target = zcu.getTarget();
+        const classes = x86_64_abi.classifySystemV(ty, zcu, target, .arg);
         if (classes[0] == .memory) {
             it.zig_index += 1;
             it.llvm_index += 1;
             it.byval_attr = true;
             return .byref;
         }
-        if (isScalar(mod, ty)) {
+        if (isScalar(zcu, ty)) {
             it.zig_index += 1;
             it.llvm_index += 1;
             return .byval;
diff --git a/src/link.zig b/src/link.zig
index 8b28a17b9d..8aec0799e2 100644
--- a/src/link.zig
+++ b/src/link.zig
@@ -19,6 +19,8 @@ const InternPool = @import("InternPool.zig");
 const Type = @import("type.zig").Type;
 const Value = @import("Value.zig");
 const LlvmObject = @import("codegen/llvm.zig").Object;
+const lldMain = @import("main.zig").lldMain;
+const Package = @import("Package.zig");
 
 /// When adding a new field, remember to update `hashAddSystemLibs`.
 /// These are *always* dynamically linked. Static libraries will be
@@ -982,3 +984,113 @@ pub const File = struct {
     pub const NvPtx = @import("link/NvPtx.zig");
     pub const Dwarf = @import("link/Dwarf.zig");
 };
+
+pub fn spawnLld(
+    comp: *Compilation,
+    arena: Allocator,
+    argv: []const []const u8,
+) !void {
+    if (comp.verbose_link) {
+        // Skip over our own name so that the LLD linker name is the first argv item.
+        Compilation.dump_argv(argv[1..]);
+    }
+
+    // If possible, we run LLD as a child process because it does not always
+    // behave properly as a library, unfortunately.
+    // https://github.com/ziglang/zig/issues/3825
+    if (!std.process.can_spawn) {
+        const exit_code = try lldMain(arena, argv, false);
+        if (exit_code == 0) return;
+        if (comp.clang_passthrough_mode) std.process.exit(exit_code);
+        return error.LLDReportedFailure;
+    }
+
+    var stderr: []u8 = &.{};
+    defer comp.gpa.free(stderr);
+
+    var child = std.process.Child.init(argv, arena);
+    const term = (if (comp.clang_passthrough_mode) term: {
+        child.stdin_behavior = .Inherit;
+        child.stdout_behavior = .Inherit;
+        child.stderr_behavior = .Inherit;
+
+        break :term child.spawnAndWait();
+    } else term: {
+        child.stdin_behavior = .Ignore;
+        child.stdout_behavior = .Ignore;
+        child.stderr_behavior = .Pipe;
+
+        child.spawn() catch |err| break :term err;
+        stderr = try child.stderr.?.reader().readAllAlloc(comp.gpa, std.math.maxInt(usize));
+        break :term child.wait();
+    }) catch |first_err| term: {
+        const err = switch (first_err) {
+            error.NameTooLong => err: {
+                const s = fs.path.sep_str;
+                const rand_int = std.crypto.random.int(u64);
+                const rsp_path = "tmp" ++ s ++ Package.Manifest.hex64(rand_int) ++ ".rsp";
+
+                const rsp_file = try comp.local_cache_directory.handle.createFileZ(rsp_path, .{});
+                defer comp.local_cache_directory.handle.deleteFileZ(rsp_path) catch |err|
+                    log.warn("failed to delete response file {s}: {s}", .{ rsp_path, @errorName(err) });
+                {
+                    defer rsp_file.close();
+                    var rsp_buf = std.io.bufferedWriter(rsp_file.writer());
+                    const rsp_writer = rsp_buf.writer();
+                    for (argv[2..]) |arg| {
+                        try rsp_writer.writeByte('"');
+                        for (arg) |c| {
+                            switch (c) {
+                                '\"', '\\' => try rsp_writer.writeByte('\\'),
+                                else => {},
+                            }
+                            try rsp_writer.writeByte(c);
+                        }
+                        try rsp_writer.writeByte('"');
+                        try rsp_writer.writeByte('\n');
+                    }
+                    try rsp_buf.flush();
+                }
+
+                var rsp_child = std.process.Child.init(&.{ argv[0], argv[1], try std.fmt.allocPrint(
+                    arena,
+                    "@{s}",
+                    .{try comp.local_cache_directory.join(arena, &.{rsp_path})},
+                ) }, arena);
+                if (comp.clang_passthrough_mode) {
+                    rsp_child.stdin_behavior = .Inherit;
+                    rsp_child.stdout_behavior = .Inherit;
+                    rsp_child.stderr_behavior = .Inherit;
+
+                    break :term rsp_child.spawnAndWait() catch |err| break :err err;
+                } else {
+                    rsp_child.stdin_behavior = .Ignore;
+                    rsp_child.stdout_behavior = .Ignore;
+                    rsp_child.stderr_behavior = .Pipe;
+
+                    rsp_child.spawn() catch |err| break :err err;
+                    stderr = try rsp_child.stderr.?.reader().readAllAlloc(comp.gpa, std.math.maxInt(usize));
+                    break :term rsp_child.wait() catch |err| break :err err;
+                }
+            },
+            else => first_err,
+        };
+        log.err("unable to spawn {s}: {s}", .{ argv[0], @errorName(err) });
+        return error.UnableToSpawnSelf;
+    };
+
+    switch (term) {
+        .Exited => |code| if (code != 0) {
+            if (comp.clang_passthrough_mode) std.process.exit(code);
+            comp.lockAndParseLldStderr(argv[1], stderr);
+            return error.LLDReportedFailure;
+        },
+        else => {
+            if (comp.clang_passthrough_mode) std.process.abort();
+            log.err("{s} terminated with stderr:\n{s}", .{ argv[0], stderr });
+            return error.LLDCrashed;
+        },
+    }
+
+    if (stderr.len > 0) log.warn("unexpected LLD stderr:\n{s}", .{stderr});
+}
diff --git a/src/link/Coff/lld.zig b/src/link/Coff/lld.zig
index cf9c06a70f..47753cbf01 100644
--- a/src/link/Coff/lld.zig
+++ b/src/link/Coff/lld.zig
@@ -9,7 +9,6 @@ const Cache = std.Build.Cache;
 
 const mingw = @import("../../mingw.zig");
 const link = @import("../../link.zig");
-const lldMain = @import("../../main.zig").lldMain;
 const trace = @import("../../tracy.zig").trace;
 
 const Allocator = mem.Allocator;
@@ -502,74 +501,7 @@ pub fn linkWithLLD(self: *Coff, arena: Allocator, prog_node: *std.Progress.Node)
             return error.DllImportLibraryNotFound;
         }
 
-        if (comp.verbose_link) {
-            // Skip over our own name so that the LLD linker name is the first argv item.
-            Compilation.dump_argv(argv.items[1..]);
-        }
-
-        if (std.process.can_spawn) {
-            // If possible, we run LLD as a child process because it does not always
-            // behave properly as a library, unfortunately.
-            // https://github.com/ziglang/zig/issues/3825
-            var child = std.ChildProcess.init(argv.items, arena);
-            if (comp.clang_passthrough_mode) {
-                child.stdin_behavior = .Inherit;
-                child.stdout_behavior = .Inherit;
-                child.stderr_behavior = .Inherit;
-
-                const term = child.spawnAndWait() catch |err| {
-                    log.err("unable to spawn {s}: {s}", .{ argv.items[0], @errorName(err) });
-                    return error.UnableToSpawnSelf;
-                };
-                switch (term) {
-                    .Exited => |code| {
-                        if (code != 0) {
-                            std.process.exit(code);
-                        }
-                    },
-                    else => std.process.abort(),
-                }
-            } else {
-                child.stdin_behavior = .Ignore;
-                child.stdout_behavior = .Ignore;
-                child.stderr_behavior = .Pipe;
-
-                try child.spawn();
-
-                const stderr = try child.stderr.?.reader().readAllAlloc(arena, std.math.maxInt(usize));
-
-                const term = child.wait() catch |err| {
-                    log.err("unable to spawn {s}: {s}", .{ argv.items[0], @errorName(err) });
-                    return error.UnableToSpawnSelf;
-                };
-
-                switch (term) {
-                    .Exited => |code| {
-                        if (code != 0) {
-                            comp.lockAndParseLldStderr(linker_command, stderr);
-                            return error.LLDReportedFailure;
-                        }
-                    },
-                    else => {
-                        log.err("{s} terminated with stderr:\n{s}", .{ argv.items[0], stderr });
-                        return error.LLDCrashed;
-                    },
-                }
-
-                if (stderr.len != 0) {
-                    log.warn("unexpected LLD stderr:\n{s}", .{stderr});
-                }
-            }
-        } else {
-            const exit_code = try lldMain(arena, argv.items, false);
-            if (exit_code != 0) {
-                if (comp.clang_passthrough_mode) {
-                    std.process.exit(exit_code);
-                } else {
-                    return error.LLDReportedFailure;
-                }
-            }
-        }
+        try link.spawnLld(comp, arena, argv.items);
     }
 
     if (!self.base.disable_lld_caching) {
diff --git a/src/link/Elf.zig b/src/link/Elf.zig
index 03451d140e..83a3d91346 100644
--- a/src/link/Elf.zig
+++ b/src/link/Elf.zig
@@ -205,10 +205,19 @@ num_ifunc_dynrelocs: usize = 0,
 
 /// List of atoms that are owned directly by the linker.
 atoms: std.ArrayListUnmanaged(Atom) = .{},
+atoms_extra: std.ArrayListUnmanaged(u32) = .{},
 
 /// List of range extension thunks.
 thunks: std.ArrayListUnmanaged(Thunk) = .{},
 
+/// List of output merge sections with deduped contents.
+merge_sections: std.ArrayListUnmanaged(MergeSection) = .{},
+/// List of output merge subsections.
+/// Each subsection is akin to Atom but belongs to a MergeSection.
+merge_subsections: std.ArrayListUnmanaged(MergeSubsection) = .{},
+/// List of input merge sections as parsed from input relocatables.
+merge_input_sections: std.ArrayListUnmanaged(InputMergeSection) = .{},
+
 /// Table of last atom index in a section and matching atom free list if any.
 last_atom_and_free_list_table: LastAtomAndFreeListTable = .{},
 
@@ -369,6 +378,7 @@ pub fn createEmpty(
     try self.symbols_extra.append(gpa, 0);
     // Allocate atom index 0 to null atom
     try self.atoms.append(gpa, .{});
+    try self.atoms_extra.append(gpa, 0);
     // Append null file at index 0
     try self.files.append(gpa, .null);
     // Append null byte to string tables
@@ -378,6 +388,8 @@ pub fn createEmpty(
     _ = try self.addSection(.{ .name = "" });
     // Append null symbol in output symtab
     try self.symtab.append(gpa, null_sym);
+    // Append null input merge section.
+    try self.merge_input_sections.append(gpa, .{});
 
     if (!is_obj_or_ar) {
         try self.dynstrtab.append(gpa, 0);
@@ -491,7 +503,20 @@ pub fn deinit(self: *Elf) void {
     self.start_stop_indexes.deinit(gpa);
 
     self.atoms.deinit(gpa);
+    self.atoms_extra.deinit(gpa);
+    for (self.thunks.items) |*th| {
+        th.deinit(gpa);
+    }
     self.thunks.deinit(gpa);
+    for (self.merge_sections.items) |*sect| {
+        sect.deinit(gpa);
+    }
+    self.merge_sections.deinit(gpa);
+    self.merge_subsections.deinit(gpa);
+    for (self.merge_input_sections.items) |*sect| {
+        sect.deinit(gpa);
+    }
+    self.merge_input_sections.deinit(gpa);
     for (self.last_atom_and_free_list_table.values()) |*value| {
         value.free_list.deinit(gpa);
     }
@@ -623,7 +648,6 @@ pub fn initMetadata(self: *Elf, options: InitMetadataOptions) !void {
     const ptr_size = self.ptrWidthBytes();
     const target = self.base.comp.root_mod.resolved_target.result;
     const ptr_bit_width = target.ptrBitWidth();
-    const is_linux = target.os.tag == .linux;
     const zig_object = self.zigObjectPtr().?;
 
     const fillSection = struct {
@@ -659,9 +683,7 @@ pub fn initMetadata(self: *Elf, options: InitMetadataOptions) !void {
         }
 
         if (self.phdr_zig_got_index == null) {
-            // We really only need ptr alignment but since we are using PROGBITS, linux requires
-            // page align.
-            const alignment = if (is_linux) self.page_size else @as(u16, ptr_size);
+            const alignment = self.page_size;
             const filesz = @as(u64, ptr_size) * options.symbol_count_hint;
             const off = self.findFreeSpace(filesz, alignment);
             self.phdr_zig_got_index = try self.addPhdr(.{
@@ -676,7 +698,7 @@ pub fn initMetadata(self: *Elf, options: InitMetadataOptions) !void {
         }
 
         if (self.phdr_zig_load_ro_index == null) {
-            const alignment = if (is_linux) self.page_size else @as(u16, ptr_size);
+            const alignment = self.page_size;
             const filesz: u64 = 1024;
             const off = self.findFreeSpace(filesz, alignment);
             self.phdr_zig_load_ro_index = try self.addPhdr(.{
@@ -691,7 +713,7 @@ pub fn initMetadata(self: *Elf, options: InitMetadataOptions) !void {
         }
 
         if (self.phdr_zig_load_rw_index == null) {
-            const alignment = if (is_linux) self.page_size else @as(u16, ptr_size);
+            const alignment = self.page_size;
             const filesz: u64 = 1024;
             const off = self.findFreeSpace(filesz, alignment);
             self.phdr_zig_load_rw_index = try self.addPhdr(.{
@@ -706,7 +728,7 @@ pub fn initMetadata(self: *Elf, options: InitMetadataOptions) !void {
         }
 
         if (self.phdr_zig_load_zerofill_index == null) {
-            const alignment = if (is_linux) self.page_size else @as(u16, ptr_size);
+            const alignment = self.page_size;
             self.phdr_zig_load_zerofill_index = try self.addPhdr(.{
                 .type = elf.PT_LOAD,
                 .addr = if (ptr_bit_width >= 32) 0x14000000 else 0xf000,
@@ -1289,6 +1311,7 @@ pub fn flushModule(self: *Elf, arena: Allocator, prog_node: *std.Progress.Node)
     // symbol for potential resolution at load-time.
     self.resolveSymbols();
     self.markEhFrameAtomsDead();
+    try self.resolveMergeSections();
 
     try self.convertCommonSymbols();
     self.markImportsExports();
@@ -1313,7 +1336,10 @@ pub fn flushModule(self: *Elf, arena: Allocator, prog_node: *std.Progress.Node)
         else => |e| return e,
     };
 
+    try self.addCommentString();
+    try self.finalizeMergeSections();
     try self.initOutputSections();
+    try self.initMergeSections();
     try self.addLinkerDefinedSymbols();
     self.claimUnresolved();
 
@@ -1332,6 +1358,7 @@ pub fn flushModule(self: *Elf, arena: Allocator, prog_node: *std.Progress.Node)
     self.sortDynamicSymtab();
     try self.setHashSections();
     try self.setVersionSymtab();
+    try self.updateMergeSectionSizes();
     try self.updateSectionSizes();
 
     try self.allocatePhdrTable();
@@ -1359,7 +1386,7 @@ pub fn flushModule(self: *Elf, arena: Allocator, prog_node: *std.Progress.Node)
             if (shdr.sh_type == elf.SHT_NOBITS) continue;
             const code = try zig_object.codeAlloc(self, atom_index);
             defer gpa.free(code);
-            const file_offset = shdr.sh_offset + atom_ptr.value;
+            const file_offset = shdr.sh_offset + @as(u64, @intCast(atom_ptr.value));
             atom_ptr.resolveRelocsAlloc(self, code) catch |err| switch (err) {
                 error.RelocFailure, error.RelaxFailure => has_reloc_errors = true,
                 error.UnsupportedCpuArch => {
@@ -1377,6 +1404,7 @@ pub fn flushModule(self: *Elf, arena: Allocator, prog_node: *std.Progress.Node)
     try self.writePhdrTable();
     try self.writeShdrTable();
     try self.writeAtoms();
+    try self.writeMergeSections();
     self.writeSyntheticSections() catch |err| switch (err) {
         error.RelocFailure => return error.FlushFailure,
         error.UnsupportedCpuArch => {
@@ -2480,7 +2508,7 @@ fn linkWithLLD(self: *Elf, arena: Allocator, prog_node: *std.Progress.Node) !voi
             try argv.append("-pie");
         }
 
-        if (is_dyn_lib and target.os.tag == .netbsd) {
+        if (is_exe_or_dyn_lib and target.os.tag == .netbsd) {
             // Add options to produce shared objects with only 2 PT_LOAD segments.
             // NetBSD expects 2 PT_LOAD segments in a shared object, otherwise
             // ld.elf_so fails loading dynamic libraries with "not found" error.
@@ -2698,74 +2726,7 @@ fn linkWithLLD(self: *Elf, arena: Allocator, prog_node: *std.Progress.Node) !voi
             try argv.append("-Bsymbolic");
         }
 
-        if (comp.verbose_link) {
-            // Skip over our own name so that the LLD linker name is the first argv item.
-            Compilation.dump_argv(argv.items[1..]);
-        }
-
-        if (std.process.can_spawn) {
-            // If possible, we run LLD as a child process because it does not always
-            // behave properly as a library, unfortunately.
-            // https://github.com/ziglang/zig/issues/3825
-            var child = std.ChildProcess.init(argv.items, arena);
-            if (comp.clang_passthrough_mode) {
-                child.stdin_behavior = .Inherit;
-                child.stdout_behavior = .Inherit;
-                child.stderr_behavior = .Inherit;
-
-                const term = child.spawnAndWait() catch |err| {
-                    log.err("unable to spawn {s}: {s}", .{ argv.items[0], @errorName(err) });
-                    return error.UnableToSpawnSelf;
-                };
-                switch (term) {
-                    .Exited => |code| {
-                        if (code != 0) {
-                            std.process.exit(code);
-                        }
-                    },
-                    else => std.process.abort(),
-                }
-            } else {
-                child.stdin_behavior = .Ignore;
-                child.stdout_behavior = .Ignore;
-                child.stderr_behavior = .Pipe;
-
-                try child.spawn();
-
-                const stderr = try child.stderr.?.reader().readAllAlloc(arena, std.math.maxInt(usize));
-
-                const term = child.wait() catch |err| {
-                    log.err("unable to spawn {s}: {s}", .{ argv.items[0], @errorName(err) });
-                    return error.UnableToSpawnSelf;
-                };
-
-                switch (term) {
-                    .Exited => |code| {
-                        if (code != 0) {
-                            comp.lockAndParseLldStderr(linker_command, stderr);
-                            return error.LLDReportedFailure;
-                        }
-                    },
-                    else => {
-                        log.err("{s} terminated with stderr:\n{s}", .{ argv.items[0], stderr });
-                        return error.LLDCrashed;
-                    },
-                }
-
-                if (stderr.len != 0) {
-                    log.warn("unexpected LLD stderr:\n{s}", .{stderr});
-                }
-            }
-        } else {
-            const exit_code = try lldMain(arena, argv.items, false);
-            if (exit_code != 0) {
-                if (comp.clang_passthrough_mode) {
-                    std.process.exit(exit_code);
-                } else {
-                    return error.LLDReportedFailure;
-                }
-            }
-        }
+        try link.spawnLld(comp, arena, argv.items);
     }
 
     if (!self.base.disable_lld_caching) {
@@ -2946,7 +2907,10 @@ pub fn writeElfHeader(self: *Elf) !void {
     mem.writeInt(u32, hdr_buf[index..][0..4], 1, endian);
     index += 4;
 
-    const e_entry = if (self.entry_index) |entry_index| self.symbol(entry_index).address(.{}, self) else 0;
+    const e_entry = if (self.entry_index) |entry_index|
+        @as(u64, @intCast(self.symbol(entry_index).address(.{}, self)))
+    else
+        0;
     const phdr_table_offset = if (self.phdr_table_index) |phndx| self.phdrs.items[phndx].p_offset else 0;
     switch (self.ptr_width) {
         .p32 => {
@@ -3132,14 +3096,14 @@ fn allocateLinkerDefinedSymbols(self: *Elf) void {
     if (self.dynamic_section_index) |shndx| {
         const shdr = &self.shdrs.items[shndx];
         const symbol_ptr = self.symbol(self.dynamic_index.?);
-        symbol_ptr.value = shdr.sh_addr;
+        symbol_ptr.value = @intCast(shdr.sh_addr);
         symbol_ptr.output_section_index = shndx;
     }
 
     // __ehdr_start
     {
         const symbol_ptr = self.symbol(self.ehdr_start_index.?);
-        symbol_ptr.value = self.image_base;
+        symbol_ptr.value = @intCast(self.image_base);
         symbol_ptr.output_section_index = 1;
     }
 
@@ -3149,9 +3113,9 @@ fn allocateLinkerDefinedSymbols(self: *Elf) void {
         const end_sym = self.symbol(self.init_array_end_index.?);
         const shdr = &self.shdrs.items[shndx];
         start_sym.output_section_index = shndx;
-        start_sym.value = shdr.sh_addr;
+        start_sym.value = @intCast(shdr.sh_addr);
         end_sym.output_section_index = shndx;
-        end_sym.value = shdr.sh_addr + shdr.sh_size;
+        end_sym.value = @intCast(shdr.sh_addr + shdr.sh_size);
     }
 
     // __fini_array_start, __fini_array_end
@@ -3160,9 +3124,9 @@ fn allocateLinkerDefinedSymbols(self: *Elf) void {
         const end_sym = self.symbol(self.fini_array_end_index.?);
         const shdr = &self.shdrs.items[shndx];
         start_sym.output_section_index = shndx;
-        start_sym.value = shdr.sh_addr;
+        start_sym.value = @intCast(shdr.sh_addr);
         end_sym.output_section_index = shndx;
-        end_sym.value = shdr.sh_addr + shdr.sh_size;
+        end_sym.value = @intCast(shdr.sh_addr + shdr.sh_size);
     }
 
     // __preinit_array_start, __preinit_array_end
@@ -3171,9 +3135,9 @@ fn allocateLinkerDefinedSymbols(self: *Elf) void {
         const end_sym = self.symbol(self.preinit_array_end_index.?);
         const shdr = &self.shdrs.items[shndx];
         start_sym.output_section_index = shndx;
-        start_sym.value = shdr.sh_addr;
+        start_sym.value = @intCast(shdr.sh_addr);
         end_sym.output_section_index = shndx;
-        end_sym.value = shdr.sh_addr + shdr.sh_size;
+        end_sym.value = @intCast(shdr.sh_addr + shdr.sh_size);
     }
 
     // _GLOBAL_OFFSET_TABLE_
@@ -3181,14 +3145,14 @@ fn allocateLinkerDefinedSymbols(self: *Elf) void {
         if (self.got_plt_section_index) |shndx| {
             const shdr = self.shdrs.items[shndx];
             const sym = self.symbol(self.got_index.?);
-            sym.value = shdr.sh_addr;
+            sym.value = @intCast(shdr.sh_addr);
             sym.output_section_index = shndx;
         }
     } else {
         if (self.got_section_index) |shndx| {
             const shdr = self.shdrs.items[shndx];
             const sym = self.symbol(self.got_index.?);
-            sym.value = shdr.sh_addr;
+            sym.value = @intCast(shdr.sh_addr);
             sym.output_section_index = shndx;
         }
     }
@@ -3197,7 +3161,7 @@ fn allocateLinkerDefinedSymbols(self: *Elf) void {
     if (self.plt_section_index) |shndx| {
         const shdr = &self.shdrs.items[shndx];
         const symbol_ptr = self.symbol(self.plt_index.?);
-        symbol_ptr.value = shdr.sh_addr;
+        symbol_ptr.value = @intCast(shdr.sh_addr);
         symbol_ptr.output_section_index = shndx;
     }
 
@@ -3205,7 +3169,7 @@ fn allocateLinkerDefinedSymbols(self: *Elf) void {
     if (self.dso_handle_index) |index| {
         const shdr = &self.shdrs.items[1];
         const symbol_ptr = self.symbol(index);
-        symbol_ptr.value = shdr.sh_addr;
+        symbol_ptr.value = @intCast(shdr.sh_addr);
         symbol_ptr.output_section_index = 0;
     }
 
@@ -3213,7 +3177,7 @@ fn allocateLinkerDefinedSymbols(self: *Elf) void {
     if (self.eh_frame_hdr_section_index) |shndx| {
         const shdr = &self.shdrs.items[shndx];
         const symbol_ptr = self.symbol(self.gnu_eh_frame_hdr_index.?);
-        symbol_ptr.value = shdr.sh_addr;
+        symbol_ptr.value = @intCast(shdr.sh_addr);
         symbol_ptr.output_section_index = shndx;
     }
 
@@ -3225,9 +3189,9 @@ fn allocateLinkerDefinedSymbols(self: *Elf) void {
         const start_addr = end_addr - self.calcNumIRelativeRelocs() * @sizeOf(elf.Elf64_Rela);
         const start_sym = self.symbol(self.rela_iplt_start_index.?);
         const end_sym = self.symbol(self.rela_iplt_end_index.?);
-        start_sym.value = start_addr;
+        start_sym.value = @intCast(start_addr);
         start_sym.output_section_index = shndx;
-        end_sym.value = end_addr;
+        end_sym.value = @intCast(end_addr);
         end_sym.output_section_index = shndx;
     }
 
@@ -3236,7 +3200,7 @@ fn allocateLinkerDefinedSymbols(self: *Elf) void {
         const end_symbol = self.symbol(self.end_index.?);
         for (self.shdrs.items, 0..) |shdr, shndx| {
             if (shdr.sh_flags & elf.SHF_ALLOC != 0) {
-                end_symbol.value = shdr.sh_addr + shdr.sh_size;
+                end_symbol.value = @intCast(shdr.sh_addr + shdr.sh_size);
                 end_symbol.output_section_index = @intCast(shndx);
             }
         }
@@ -3251,9 +3215,9 @@ fn allocateLinkerDefinedSymbols(self: *Elf) void {
             const stop = self.symbol(self.start_stop_indexes.items[index + 1]);
             const shndx = self.sectionByName(name["__start_".len..]).?;
             const shdr = &self.shdrs.items[shndx];
-            start.value = shdr.sh_addr;
+            start.value = @intCast(shdr.sh_addr);
             start.output_section_index = shndx;
-            stop.value = shdr.sh_addr + shdr.sh_size;
+            stop.value = @intCast(shdr.sh_addr + shdr.sh_size);
             stop.output_section_index = shndx;
         }
     }
@@ -3263,7 +3227,7 @@ fn allocateLinkerDefinedSymbols(self: *Elf) void {
         const sym = self.symbol(index);
         if (self.sectionByName(".sdata")) |shndx| {
             const shdr = self.shdrs.items[shndx];
-            sym.value = shdr.sh_addr + 0x800;
+            sym.value = @intCast(shdr.sh_addr + 0x800);
             sym.output_section_index = shndx;
         } else {
             sym.value = 0;
@@ -3293,12 +3257,122 @@ fn checkDuplicates(self: *Elf) !void {
     try self.reportDuplicates(dupes);
 }
 
+pub fn addCommentString(self: *Elf) !void {
+    const msec_index = try self.getOrCreateMergeSection(".comment", elf.SHF_MERGE | elf.SHF_STRINGS, elf.SHT_PROGBITS);
+    const msec = self.mergeSection(msec_index);
+    const res = try msec.insertZ(self.base.comp.gpa, "zig " ++ builtin.zig_version_string);
+    if (res.found_existing) return;
+    const msub_index = try self.addMergeSubsection();
+    const msub = self.mergeSubsection(msub_index);
+    msub.merge_section_index = msec_index;
+    msub.string_index = res.key.pos;
+    msub.alignment = .@"1";
+    msub.size = res.key.len;
+    msub.entsize = 1;
+    msub.alive = true;
+    res.sub.* = msub_index;
+}
+
+pub fn resolveMergeSections(self: *Elf) !void {
+    const tracy = trace(@src());
+    defer tracy.end();
+
+    var has_errors = false;
+    for (self.objects.items) |index| {
+        const file_ptr = self.file(index).?;
+        if (!file_ptr.isAlive()) continue;
+        file_ptr.object.initMergeSections(self) catch |err| switch (err) {
+            error.MalformedObject => has_errors = true,
+            else => |e| return e,
+        };
+    }
+
+    if (has_errors) return error.FlushFailure;
+
+    for (self.objects.items) |index| {
+        const file_ptr = self.file(index).?;
+        if (!file_ptr.isAlive()) continue;
+        file_ptr.object.resolveMergeSubsections(self) catch |err| switch (err) {
+            error.MalformedObject => has_errors = true,
+            else => |e| return e,
+        };
+    }
+
+    if (has_errors) return error.FlushFailure;
+}
+
+pub fn finalizeMergeSections(self: *Elf) !void {
+    for (self.merge_sections.items) |*msec| {
+        try msec.finalize(self);
+    }
+}
+
+pub fn updateMergeSectionSizes(self: *Elf) !void {
+    for (self.merge_sections.items) |*msec| {
+        const shdr = &self.shdrs.items[msec.output_section_index];
+        for (msec.subsections.items) |msub_index| {
+            const msub = self.mergeSubsection(msub_index);
+            assert(msub.alive);
+            const offset = msub.alignment.forward(shdr.sh_size);
+            const padding = offset - shdr.sh_size;
+            msub.value = @intCast(offset);
+            shdr.sh_size += padding + msub.size;
+            shdr.sh_addralign = @max(shdr.sh_addralign, msub.alignment.toByteUnits() orelse 1);
+        }
+    }
+}
+
+pub fn writeMergeSections(self: *Elf) !void {
+    const gpa = self.base.comp.gpa;
+    var buffer = std.ArrayList(u8).init(gpa);
+    defer buffer.deinit();
+
+    for (self.merge_sections.items) |msec| {
+        const shdr = self.shdrs.items[msec.output_section_index];
+        const size = math.cast(usize, shdr.sh_size) orelse return error.Overflow;
+        try buffer.ensureTotalCapacity(size);
+        buffer.appendNTimesAssumeCapacity(0, size);
+
+        for (msec.subsections.items) |msub_index| {
+            const msub = self.mergeSubsection(msub_index);
+            assert(msub.alive);
+            const string = msub.getString(self);
+            const off = math.cast(usize, msub.value) orelse return error.Overflow;
+            @memcpy(buffer.items[off..][0..string.len], string);
+        }
+
+        try self.base.file.?.pwriteAll(buffer.items, shdr.sh_offset);
+        buffer.clearRetainingCapacity();
+    }
+}
+
 fn initOutputSections(self: *Elf) !void {
     for (self.objects.items) |index| {
         try self.file(index).?.object.initOutputSections(self);
     }
 }
 
+pub fn initMergeSections(self: *Elf) !void {
+    for (self.merge_sections.items) |*msec| {
+        if (msec.subsections.items.len == 0) continue;
+        const name = msec.name(self);
+        const shndx = self.sectionByName(name) orelse try self.addSection(.{
+            .name = name,
+            .type = msec.type,
+            .flags = msec.flags,
+        });
+        msec.output_section_index = shndx;
+
+        var entsize = self.mergeSubsection(msec.subsections.items[0]).entsize;
+        for (msec.subsections.items) |index| {
+            const msub = self.mergeSubsection(index);
+            entsize = @min(entsize, msub.entsize);
+        }
+        const shdr = &self.shdrs.items[shndx];
+        shdr.sh_entsize = entsize;
+    }
+}
+
 fn initSyntheticSections(self: *Elf) !void {
     const comp = self.base.comp;
     const target = comp.root_mod.resolved_target.result;
@@ -3965,6 +4039,10 @@ fn resetShdrIndexes(self: *Elf, backlinks: []const u32) !void {
         }
     }
 
+    for (self.merge_sections.items) |*msec| {
+        msec.output_section_index = backlinks[msec.output_section_index];
+    }
+
     {
         var output_rela_sections = try self.output_rela_sections.clone(gpa);
         defer output_rela_sections.deinit(gpa);
@@ -4052,7 +4130,7 @@ fn updateSectionSizes(self: *Elf) !void {
             if (!atom_ptr.flags.alive) continue;
             const offset = atom_ptr.alignment.forward(shdr.sh_size);
             const padding = offset - shdr.sh_size;
-            atom_ptr.value = offset;
+            atom_ptr.value = @intCast(offset);
             shdr.sh_size += padding + atom_ptr.size;
             shdr.sh_addralign = @max(shdr.sh_addralign, atom_ptr.alignment.toByteUnits() orelse 1);
         }
@@ -4535,7 +4613,7 @@ fn writeAtoms(self: *Elf) !void {
             const atom_ptr = self.atom(atom_index).?;
             assert(atom_ptr.flags.alive);
 
-            const offset = math.cast(usize, atom_ptr.value - base_offset) orelse
+            const offset = math.cast(usize, atom_ptr.value - @as(i64, @intCast(base_offset))) orelse
                 return error.Overflow;
             const size = math.cast(usize, atom_ptr.size) orelse return error.Overflow;
 
@@ -4576,7 +4654,7 @@ fn writeAtoms(self: *Elf) !void {
             const thunk_size = th.size(self);
             try buffer.ensureUnusedCapacity(thunk_size);
             const shdr = self.shdrs.items[th.output_section_index];
-            const offset = th.value + shdr.sh_offset;
+            const offset = @as(u64, @intCast(th.value)) + shdr.sh_offset;
             try th.write(self, buffer.writer());
             assert(buffer.items.len == thunk_size);
             try self.base.file.?.pwriteAll(buffer.items, offset);
@@ -4611,6 +4689,7 @@ pub fn updateSymtabSize(self: *Elf) !void {
     if (self.eh_frame_section_index) |_| {
         nlocals += 1;
     }
+    nlocals += @intCast(self.merge_sections.items.len);
 
     if (self.requiresThunks()) for (self.thunks.items) |*th| {
         th.output_symtab_ctx.ilocal = nlocals + 1;
@@ -4947,12 +5026,30 @@ fn writeSectionSymbols(self: *Elf) void {
         };
         ilocal += 1;
     }
+
+    for (self.merge_sections.items) |msec| {
+        const shdr = self.shdrs.items[msec.output_section_index];
+        const out_sym = &self.symtab.items[ilocal];
+        out_sym.* = .{
+            .st_name = 0,
+            .st_value = shdr.sh_addr,
+            .st_info = elf.STT_SECTION,
+            .st_shndx = @intCast(msec.output_section_index),
+            .st_size = 0,
+            .st_other = 0,
+        };
+        ilocal += 1;
+    }
 }
 
 pub fn sectionSymbolOutputSymtabIndex(self: Elf, shndx: u32) u32 {
     if (self.eh_frame_section_index) |index| {
         if (index == shndx) return @intCast(self.output_sections.keys().len + 1);
     }
+    const base: usize = if (self.eh_frame_section_index == null) 0 else 1;
+    for (self.merge_sections.items, 0..) |msec, index| {
+        if (msec.output_section_index == shndx) return @intCast(self.output_sections.keys().len + 1 + index + base);
+    }
     return @intCast(self.output_sections.getIndex(shndx).? + 1);
 }
 
@@ -5003,9 +5100,9 @@ fn getLDMOption(target: std.Target) ?[]const u8 {
     switch (target.cpu.arch) {
         .x86 => return "elf_i386",
         .aarch64 => return "aarch64linux",
-        .aarch64_be => return "aarch64_be_linux",
+        .aarch64_be => return "aarch64linuxb",
         .arm, .thumb => return "armelf_linux_eabi",
-        .armeb, .thumbeb => return "armebelf_linux_eabi",
+        .armeb, .thumbeb => return "armelfb_linux_eabi",
         .powerpc => return "elf32ppclinux",
         .powerpc64 => return "elf64ppc",
         .powerpc64le => return "elf64lppc",
@@ -5458,6 +5555,50 @@ pub fn addAtom(self: *Elf) !Atom.Index {
     return index;
 }
 
+pub fn addAtomExtra(self: *Elf, extra: Atom.Extra) !u32 {
+    const fields = @typeInfo(Atom.Extra).Struct.fields;
+    try self.atoms_extra.ensureUnusedCapacity(self.base.comp.gpa, fields.len);
+    return self.addAtomExtraAssumeCapacity(extra);
+}
+
+pub fn addAtomExtraAssumeCapacity(self: *Elf, extra: Atom.Extra) u32 {
+    const index = @as(u32, @intCast(self.atoms_extra.items.len));
+    const fields = @typeInfo(Atom.Extra).Struct.fields;
+    inline for (fields) |field| {
+        self.atoms_extra.appendAssumeCapacity(switch (field.type) {
+            u32 => @field(extra, field.name),
+            else => @compileError("bad field type"),
+        });
+    }
+    return index;
+}
+
+pub fn atomExtra(self: *Elf, index: u32) ?Atom.Extra {
+    if (index == 0) return null;
+    const fields = @typeInfo(Atom.Extra).Struct.fields;
+    var i: usize = index;
+    var result: Atom.Extra = undefined;
+    inline for (fields) |field| {
+        @field(result, field.name) = switch (field.type) {
+            u32 => self.atoms_extra.items[i],
+            else => @compileError("bad field type"),
+        };
+        i += 1;
+    }
+    return result;
+}
+
+pub fn setAtomExtra(self: *Elf, index: u32, extra: Atom.Extra) void {
+    assert(index > 0);
+    const fields = @typeInfo(Atom.Extra).Struct.fields;
+    inline for (fields, 0..) |field, i| {
+        self.atoms_extra.items[index + i] = switch (field.type) {
+            u32 => @field(extra, field.name),
+            else => @compileError("bad field type"),
+        };
+    }
+}
+
 pub fn addThunk(self: *Elf) !Thunk.Index {
     const index = @as(Thunk.Index, @intCast(self.thunks.items.len));
     const th = try self.thunks.addOne(self.base.comp.gpa);
@@ -5637,35 +5778,88 @@ pub fn comdatGroupOwner(self: *Elf, index: ComdatGroupOwner.Index) *ComdatGroupO
     return &self.comdat_groups_owners.items[index];
 }
 
-pub fn gotAddress(self: *Elf) u64 {
+pub fn addInputMergeSection(self: *Elf) !InputMergeSection.Index {
+    const index: InputMergeSection.Index = @intCast(self.merge_input_sections.items.len);
+    const msec = try self.merge_input_sections.addOne(self.base.comp.gpa);
+    msec.* = .{};
+    return index;
+}
+
+pub fn inputMergeSection(self: *Elf, index: InputMergeSection.Index) ?*InputMergeSection {
+    if (index == 0) return null;
+    return &self.merge_input_sections.items[index];
+}
+
+pub fn addMergeSubsection(self: *Elf) !MergeSubsection.Index {
+    const index: MergeSubsection.Index = @intCast(self.merge_subsections.items.len);
+    const msec = try self.merge_subsections.addOne(self.base.comp.gpa);
+    msec.* = .{};
+    return index;
+}
+
+pub fn mergeSubsection(self: *Elf, index: MergeSubsection.Index) *MergeSubsection {
+    assert(index < self.merge_subsections.items.len);
+    return &self.merge_subsections.items[index];
+}
+
+pub fn getOrCreateMergeSection(self: *Elf, name: []const u8, flags: u64, @"type": u32) !MergeSection.Index {
+    const gpa = self.base.comp.gpa;
+    const out_name = name: {
+        if (self.base.isRelocatable()) break :name name;
+        if (mem.eql(u8, name, ".rodata") or mem.startsWith(u8, name, ".rodata"))
+            break :name if (flags & elf.SHF_STRINGS != 0) ".rodata.str" else ".rodata.cst";
+        break :name name;
+    };
+    const out_off = try self.strings.insert(gpa, out_name);
+    const out_flags = flags & ~@as(u64, elf.SHF_COMPRESSED | elf.SHF_GROUP);
+    for (self.merge_sections.items, 0..) |msec, index| {
+        if (msec.name_offset == out_off) return @intCast(index);
+    }
+    const index = @as(MergeSection.Index, @intCast(self.merge_sections.items.len));
+    const msec = try self.merge_sections.addOne(gpa);
+    msec.* = .{
+        .name_offset = out_off,
+        .flags = out_flags,
+        .type = @"type",
+    };
+    return index;
+}
+
+pub fn mergeSection(self: *Elf, index: MergeSection.Index) *MergeSection {
+    assert(index < self.merge_sections.items.len);
+    return &self.merge_sections.items[index];
+}
+
+pub fn gotAddress(self: *Elf) i64 {
     const shndx = blk: {
         if (self.getTarget().cpu.arch == .x86_64 and self.got_plt_section_index != null)
             break :blk self.got_plt_section_index.?;
         break :blk if (self.got_section_index) |shndx| shndx else null;
     };
-    return if (shndx) |index| self.shdrs.items[index].sh_addr else 0;
+    return if (shndx) |index| @intCast(self.shdrs.items[index].sh_addr) else 0;
 }
 
-pub fn tpAddress(self: *Elf) u64 {
+pub fn tpAddress(self: *Elf) i64 {
     const index = self.phdr_tls_index orelse return 0;
     const phdr = self.phdrs.items[index];
-    return switch (self.getTarget().cpu.arch) {
+    const addr = switch (self.getTarget().cpu.arch) {
         .x86_64 => mem.alignForward(u64, phdr.p_vaddr + phdr.p_memsz, phdr.p_align),
         .aarch64 => mem.alignBackward(u64, phdr.p_vaddr - 16, phdr.p_align),
         else => @panic("TODO implement getTpAddress for this arch"),
     };
+    return @intCast(addr);
 }
 
-pub fn dtpAddress(self: *Elf) u64 {
+pub fn dtpAddress(self: *Elf) i64 {
     const index = self.phdr_tls_index orelse return 0;
     const phdr = self.phdrs.items[index];
-    return phdr.p_vaddr;
+    return @intCast(phdr.p_vaddr);
 }
 
-pub fn tlsAddress(self: *Elf) u64 {
+pub fn tlsAddress(self: *Elf) i64 {
     const index = self.phdr_tls_index orelse return 0;
     const phdr = self.phdrs.items[index];
-    return phdr.p_vaddr;
+    return @intCast(phdr.p_vaddr);
 }
 
 const ErrorWithNotes = struct {
@@ -6043,6 +6237,11 @@ fn fmtDumpState(
         try writer.print("  shdr({d}) : COMDAT({d})\n", .{ cg.shndx, cg.cg_index });
     }
 
+    try writer.writeAll("\nOutput merge sections\n");
+    for (self.merge_sections.items) |msec| {
+        try writer.print("  shdr({d}) : {}\n", .{ msec.output_section_index, msec.fmt(self) });
+    }
+
     try writer.writeAll("\nOutput shdrs\n");
     for (self.shdrs.items, 0..) |shdr, shndx| {
         try writer.print("  shdr({d}) : phdr({?d}) : {}\n", .{
@@ -6234,7 +6433,7 @@ const eh_frame = @import("Elf/eh_frame.zig");
 const gc = @import("Elf/gc.zig");
 const glibc = @import("../glibc.zig");
 const link = @import("../link.zig");
-const lldMain = @import("../main.zig").lldMain;
+const merge_section = @import("Elf/merge_section.zig");
 const musl = @import("../musl.zig");
 const relocatable = @import("Elf/relocatable.zig");
 const relocation = @import("Elf/relocation.zig");
@@ -6260,10 +6459,13 @@ const GnuHashSection = synthetic_sections.GnuHashSection;
 const GotSection = synthetic_sections.GotSection;
 const GotPltSection = synthetic_sections.GotPltSection;
 const HashSection = synthetic_sections.HashSection;
+const InputMergeSection = merge_section.InputMergeSection;
 const LdScript = @import("Elf/LdScript.zig");
 const LinkerDefined = @import("Elf/LinkerDefined.zig");
 const Liveness = @import("../Liveness.zig");
 const LlvmObject = @import("../codegen/llvm.zig").Object;
+const MergeSection = merge_section.MergeSection;
+const MergeSubsection = merge_section.MergeSubsection;
 const Module = @import("../Module.zig");
 const Object = @import("Elf/Object.zig");
 const InternPool = @import("../InternPool.zig");
diff --git a/src/link/Elf/Archive.zig b/src/link/Elf/Archive.zig
index 76ab157bab..030ddc13c6 100644
--- a/src/link/Elf/Archive.zig
+++ b/src/link/Elf/Archive.zig
@@ -64,6 +64,7 @@ pub fn parse(self: *Archive, elf_file: *Elf, path: []const u8, handle_index: Fil
             .archive = .{
                 .path = try gpa.dupe(u8, path),
                 .offset = pos,
+                .size = obj_size,
             },
             .path = try gpa.dupe(u8, name),
             .file_handle = handle_index,
diff --git a/src/link/Elf/Atom.zig b/src/link/Elf/Atom.zig
index b5ceeb24b8..90056cc4c5 100644
--- a/src/link/Elf/Atom.zig
+++ b/src/link/Elf/Atom.zig
@@ -1,5 +1,5 @@
 /// Address allocated for this Atom.
-value: u64 = 0,
+value: i64 = 0,
 
 /// Name of this Atom.
 name_offset: u32 = 0,
@@ -22,32 +22,19 @@ output_section_index: u32 = 0,
 /// Index of the input section containing this atom's relocs.
 relocs_section_index: u32 = 0,
 
-/// Start index of the relocations belonging to this atom.
-rel_index: u32 = 0,
-
-/// Number of relocations belonging to this atom.
-rel_num: u32 = 0,
-
 /// Index of this atom in the linker's atoms table.
 atom_index: Index = 0,
 
-/// Index of the thunk for this atom.
-thunk_index: Thunk.Index = 0,
-
-/// Flags we use for state tracking.
-flags: Flags = .{},
-
-/// Start index of FDEs referencing this atom.
-fde_start: u32 = 0,
-
-/// End index of FDEs referencing this atom.
-fde_end: u32 = 0,
-
 /// Points to the previous and next neighbors, based on the `text_offset`.
 /// This can be used to find, for example, the capacity of this `TextBlock`.
 prev_index: Index = 0,
 next_index: Index = 0,
 
+/// Flags we use for state tracking.
+flags: Flags = .{},
+
+extra_index: u32 = 0,
+
 pub const Alignment = @import("../../InternPool.zig").Alignment;
 
 pub fn name(self: Atom, elf_file: *Elf) []const u8 {
@@ -57,10 +44,22 @@ pub fn name(self: Atom, elf_file: *Elf) []const u8 {
     };
 }
 
-pub fn address(self: Atom, elf_file: *Elf) u64 {
+pub fn address(self: Atom, elf_file: *Elf) i64 {
     const shndx = self.outputShndx() orelse return self.value;
     const shdr = elf_file.shdrs.items[shndx];
-    return shdr.sh_addr + self.value;
+    return @as(i64, @intCast(shdr.sh_addr)) + self.value;
+}
+
+pub fn debugTombstoneValue(self: Atom, target: Symbol, elf_file: *Elf) ?u64 {
+    if (target.mergeSubsection(elf_file)) |msub| {
+        if (msub.alive) return null;
+    }
+    if (target.atom(elf_file)) |atom_ptr| {
+        if (atom_ptr.flags.alive) return null;
+    }
+    const atom_name = self.name(elf_file);
+    if (!mem.startsWith(u8, atom_name, ".debug")) return null;
+    return if (mem.eql(u8, atom_name, ".debug_loc") or mem.eql(u8, atom_name, ".debug_ranges")) 1 else 0;
 }
 
 pub fn file(self: Atom, elf_file: *Elf) ?File {
@@ -68,7 +67,9 @@ pub fn file(self: Atom, elf_file: *Elf) ?File {
 }
 
 pub fn thunk(self: Atom, elf_file: *Elf) *Thunk {
-    return elf_file.thunk(self.thunk_index);
+    assert(self.flags.thunk);
+    const extras = self.extra(elf_file).?;
+    return elf_file.thunk(extras.thunk);
 }
 
 pub fn inputShdr(self: Atom, elf_file: *Elf) elf.Elf64_Shdr {
@@ -102,13 +103,13 @@ pub fn capacity(self: Atom, elf_file: *Elf) u64 {
         next.address(elf_file)
     else
         std.math.maxInt(u32);
-    return next_addr - self.address(elf_file);
+    return @intCast(next_addr - self.address(elf_file));
 }
 
 pub fn freeListEligible(self: Atom, elf_file: *Elf) bool {
     // No need to keep a free list node for the last block.
     const next = elf_file.atom(self.next_index) orelse return false;
-    const cap = next.address(elf_file) - self.address(elf_file);
+    const cap: u64 = @intCast(next.address(elf_file) - self.address(elf_file));
     const ideal_cap = Elf.padToIdeal(self.size);
     if (cap <= ideal_cap) return false;
     const surplus = cap - ideal_cap;
@@ -141,8 +142,8 @@ pub fn allocate(self: *Atom, elf_file: *Elf) !void {
             // Is it enough that we could fit this new atom?
             const cap = big_atom.capacity(elf_file);
             const ideal_capacity = Elf.padToIdeal(cap);
-            const ideal_capacity_end_vaddr = std.math.add(u64, big_atom.value, ideal_capacity) catch ideal_capacity;
-            const capacity_end_vaddr = big_atom.value + cap;
+            const ideal_capacity_end_vaddr = std.math.add(u64, @intCast(big_atom.value), ideal_capacity) catch ideal_capacity;
+            const capacity_end_vaddr = @as(u64, @intCast(big_atom.value)) + cap;
             const new_start_vaddr_unaligned = capacity_end_vaddr - new_atom_ideal_capacity;
             const new_start_vaddr = self.alignment.backward(new_start_vaddr_unaligned);
             if (new_start_vaddr < ideal_capacity_end_vaddr) {
@@ -167,14 +168,14 @@ pub fn allocate(self: *Atom, elf_file: *Elf) !void {
             if (!keep_free_list_node) {
                 free_list_removal = i;
             }
-            break :blk new_start_vaddr;
+            break :blk @intCast(new_start_vaddr);
         } else if (elf_file.atom(last_atom_index.*)) |last| {
             const ideal_capacity = Elf.padToIdeal(last.size);
-            const ideal_capacity_end_vaddr = last.value + ideal_capacity;
+            const ideal_capacity_end_vaddr = @as(u64, @intCast(last.value)) + ideal_capacity;
             const new_start_vaddr = self.alignment.forward(ideal_capacity_end_vaddr);
             // Set up the metadata to be updated, after errors are no longer possible.
             atom_placement = last.atom_index;
-            break :blk new_start_vaddr;
+            break :blk @intCast(new_start_vaddr);
         } else {
             break :blk 0;
         }
@@ -184,7 +185,7 @@ pub fn allocate(self: *Atom, elf_file: *Elf) !void {
         self.atom_index,
         self.name(elf_file),
         self.address(elf_file),
-        self.address(elf_file) + self.size,
+        self.address(elf_file) + @as(i64, @intCast(self.size)),
     });
 
     const expand_section = if (atom_placement) |placement_index|
@@ -192,7 +193,7 @@ pub fn allocate(self: *Atom, elf_file: *Elf) !void {
     else
         true;
     if (expand_section) {
-        const needed_size = self.value + self.size;
+        const needed_size: u64 = @intCast(self.value + @as(i64, @intCast(self.size)));
         try elf_file.growAllocSection(self.outputShndx().?, needed_size);
         last_atom_index.* = self.atom_index;
 
@@ -242,7 +243,7 @@ pub fn shrink(self: *Atom, elf_file: *Elf) void {
 }
 
 pub fn grow(self: *Atom, elf_file: *Elf) !void {
-    if (!self.alignment.check(self.value) or self.size > self.capacity(elf_file))
+    if (!self.alignment.check(@intCast(self.value)) or self.size > self.capacity(elf_file))
         try self.allocate(elf_file);
 }
 
@@ -309,11 +310,14 @@ pub fn free(self: *Atom, elf_file: *Elf) void {
 
 pub fn relocs(self: Atom, elf_file: *Elf) []const elf.Elf64_Rela {
     const shndx = self.relocsShndx() orelse return &[0]elf.Elf64_Rela{};
-    return switch (self.file(elf_file).?) {
-        .zig_object => |x| x.relocs.items[shndx].items,
-        .object => |x| x.relocs.items[self.rel_index..][0..self.rel_num],
+    switch (self.file(elf_file).?) {
+        .zig_object => |x| return x.relocs.items[shndx].items,
+        .object => |x| {
+            const extras = self.extra(elf_file).?;
+            return x.relocs.items[extras.rel_index..][0..extras.rel_count];
+        },
         else => unreachable,
-    };
+    }
 }
 
 pub fn writeRelocs(self: Atom, elf_file: *Elf, out_relocs: *std.ArrayList(elf.Elf64_Rela)) !void {
@@ -329,11 +333,14 @@ pub fn writeRelocs(self: Atom, elf_file: *Elf, out_relocs: *std.ArrayList(elf.El
         };
         const target = elf_file.symbol(target_index);
         const r_type = rel.r_type();
-        const r_offset = self.value + rel.r_offset;
+        const r_offset: u64 = @intCast(self.value + @as(i64, @intCast(rel.r_offset)));
         var r_addend = rel.r_addend;
         var r_sym: u32 = 0;
         switch (target.type(elf_file)) {
-            elf.STT_SECTION => {
+            elf.STT_SECTION => if (target.mergeSubsection(elf_file)) |msub| {
+                r_addend += @intCast(target.address(.{}, elf_file));
+                r_sym = elf_file.sectionSymbolOutputSymtabIndex(msub.mergeSection(elf_file).output_section_index);
+            } else {
                 r_addend += @intCast(target.address(.{}, elf_file));
                 r_sym = elf_file.sectionSymbolOutputSymtabIndex(target.outputShndx().?);
             },
@@ -359,9 +366,10 @@ pub fn writeRelocs(self: Atom, elf_file: *Elf, out_relocs: *std.ArrayList(elf.El
 }
 
 pub fn fdes(self: Atom, elf_file: *Elf) []Fde {
-    if (self.fde_start == self.fde_end) return &[0]Fde{};
+    if (!self.flags.fde) return &[0]Fde{};
+    const extras = self.extra(elf_file).?;
     const object = self.file(elf_file).?.object;
-    return object.fdes.items[self.fde_start..self.fde_end];
+    return object.fdes.items[extras.fde_start..][0..extras.fde_count];
 }
 
 pub fn markFdesDead(self: Atom, elf_file: *Elf) void {
@@ -419,6 +427,12 @@ pub fn scanRelocs(self: Atom, elf_file: *Elf, code: ?[]const u8, undefs: anytype
         };
         const symbol = elf_file.symbol(symbol_index);
 
+        const is_synthetic_symbol = switch (file_ptr) {
+            .zig_object => false, // TODO: implement this once we support merge sections in ZigObject
+            .object => |x| rel.r_sym() >= x.symtab.items.len,
+            else => unreachable,
+        };
+
         // Check for violation of One Definition Rule for COMDATs.
         if (symbol.file(elf_file) == null) {
             // TODO convert into an error
@@ -431,7 +445,8 @@ pub fn scanRelocs(self: Atom, elf_file: *Elf, code: ?[]const u8, undefs: anytype
         }
 
         // Report an undefined symbol.
-        if (try self.reportUndefined(elf_file, symbol, symbol_index, rel, undefs)) continue;
+        if (!is_synthetic_symbol and (try self.reportUndefined(elf_file, symbol, symbol_index, rel, undefs)))
+            continue;
 
         if (symbol.isIFunc(elf_file)) {
             symbol.flags.needs_got = true;
@@ -601,7 +616,10 @@ fn outputType(elf_file: *Elf) u2 {
     return switch (elf_file.base.comp.config.output_mode) {
         .Obj => unreachable,
         .Lib => 0,
-        .Exe => if (comp.config.pie) 1 else 2,
+        .Exe => switch (elf_file.getTarget().os.tag) {
+            .haiku => 0,
+            else => if (comp.config.pie) 1 else 2,
+        },
     };
 }
 
@@ -740,21 +758,21 @@ pub fn resolveRelocsAlloc(self: Atom, elf_file: *Elf, code: []u8) RelocError!voi
         // https://intezer.com/blog/malware-analysis/executable-and-linkable-format-101-part-3-relocations/
         //
         // Address of the source atom.
-        const P = @as(i64, @intCast(self.address(elf_file) + rel.r_offset));
+        const P = self.address(elf_file) + @as(i64, @intCast(rel.r_offset));
         // Addend from the relocation.
         const A = rel.r_addend;
         // Address of the target symbol - can be address of the symbol within an atom or address of PLT stub.
-        const S = @as(i64, @intCast(target.address(.{}, elf_file)));
+        const S = target.address(.{}, elf_file);
         // Address of the global offset table.
-        const GOT = @as(i64, @intCast(elf_file.gotAddress()));
+        const GOT = elf_file.gotAddress();
         // Address of the .zig.got table entry if any.
-        const ZIG_GOT = @as(i64, @intCast(target.zigGotAddress(elf_file)));
+        const ZIG_GOT = target.zigGotAddress(elf_file);
         // Relative offset to the start of the global offset table.
-        const G = @as(i64, @intCast(target.gotAddress(elf_file))) - GOT;
+        const G = target.gotAddress(elf_file) - GOT;
         // // Address of the thread pointer.
-        const TP = @as(i64, @intCast(elf_file.tpAddress()));
+        const TP = elf_file.tpAddress();
         // Address of the dynamic thread pointer.
-        const DTP = @as(i64, @intCast(elf_file.dtpAddress()));
+        const DTP = elf_file.dtpAddress();
 
         relocs_log.debug("  {s}: {x}: [{x} => {x}] G({x}) ZG({x}) ({s})", .{
             relocation.fmtRelocType(rel.r_type(), cpu_arch),
@@ -811,9 +829,9 @@ fn resolveDynAbsReloc(
     const comp = elf_file.base.comp;
     const gpa = comp.gpa;
     const cpu_arch = elf_file.getTarget().cpu.arch;
-    const P = self.address(elf_file) + rel.r_offset;
+    const P: u64 = @intCast(self.address(elf_file) + @as(i64, @intCast(rel.r_offset)));
     const A = rel.r_addend;
-    const S = @as(i64, @intCast(target.address(.{}, elf_file)));
+    const S = target.address(.{}, elf_file);
     const is_writeable = self.inputShdr(elf_file).sh_flags & elf.SHF_WRITE != 0;
 
     const num_dynrelocs = switch (self.file(elf_file).?) {
@@ -881,7 +899,7 @@ fn resolveDynAbsReloc(
         },
 
         .ifunc => {
-            const S_ = @as(i64, @intCast(target.address(.{ .plt = false }, elf_file)));
+            const S_ = target.address(.{ .plt = false }, elf_file);
             elf_file.addRelaDynAssumeCapacity(.{
                 .offset = P,
                 .type = relocation.encode(.irel, cpu_arch),
@@ -921,6 +939,11 @@ pub fn resolveRelocsNonAlloc(self: Atom, elf_file: *Elf, code: []u8, undefs: any
             else => unreachable,
         };
         const target = elf_file.symbol(target_index);
+        const is_synthetic_symbol = switch (file_ptr) {
+            .zig_object => false, // TODO: implement this once we support merge sections in ZigObject
+            .object => |x| rel.r_sym() >= x.symtab.items.len,
+            else => unreachable,
+        };
 
         // Check for violation of One Definition Rule for COMDATs.
         if (target.file(elf_file) == null) {
@@ -934,20 +957,21 @@ pub fn resolveRelocsNonAlloc(self: Atom, elf_file: *Elf, code: []u8, undefs: any
         }
 
         // Report an undefined symbol.
-        if (try self.reportUndefined(elf_file, target, target_index, rel, undefs)) continue;
+        if (!is_synthetic_symbol and (try self.reportUndefined(elf_file, target, target_index, rel, undefs)))
+            continue;
 
         // We will use equation format to resolve relocations:
         // https://intezer.com/blog/malware-analysis/executable-and-linkable-format-101-part-3-relocations/
         //
-        const P = @as(i64, @intCast(self.address(elf_file) + rel.r_offset));
+        const P = self.address(elf_file) + @as(i64, @intCast(rel.r_offset));
         // Addend from the relocation.
         const A = rel.r_addend;
         // Address of the target symbol - can be address of the symbol within an atom or address of PLT stub.
-        const S = @as(i64, @intCast(target.address(.{}, elf_file)));
+        const S = target.address(.{}, elf_file);
         // Address of the global offset table.
-        const GOT = @as(i64, @intCast(elf_file.gotAddress()));
+        const GOT = elf_file.gotAddress();
         // Address of the dynamic thread pointer.
-        const DTP = @as(i64, @intCast(elf_file.dtpAddress()));
+        const DTP = elf_file.dtpAddress();
 
         const args = ResolveArgs{ P, A, S, GOT, 0, 0, DTP, 0 };
 
@@ -981,6 +1005,35 @@ pub fn resolveRelocsNonAlloc(self: Atom, elf_file: *Elf, code: []u8, undefs: any
     if (has_reloc_errors) return error.RelocFailure;
 }
 
+const AddExtraOpts = struct {
+    thunk: ?u32 = null,
+    fde_start: ?u32 = null,
+    fde_count: ?u32 = null,
+    rel_index: ?u32 = null,
+    rel_count: ?u32 = null,
+};
+
+pub fn addExtra(atom: *Atom, opts: AddExtraOpts, elf_file: *Elf) !void {
+    if (atom.extra(elf_file) == null) {
+        atom.extra_index = try elf_file.addAtomExtra(.{});
+    }
+    var extras = atom.extra(elf_file).?;
+    inline for (@typeInfo(@TypeOf(opts)).Struct.fields) |field| {
+        if (@field(opts, field.name)) |x| {
+            @field(extras, field.name) = x;
+        }
+    }
+    atom.setExtra(extras, elf_file);
+}
+
+pub inline fn extra(atom: Atom, elf_file: *Elf) ?Extra {
+    return elf_file.atomExtra(atom.extra_index);
+}
+
+pub inline fn setExtra(atom: Atom, extras: Extra, elf_file: *Elf) void {
+    elf_file.setAtomExtra(atom.extra_index, extras);
+}
+
 pub fn format(
     atom: Atom,
     comptime unused_fmt_string: []const u8,
@@ -1020,12 +1073,13 @@ fn format2(
         atom.atom_index,           atom.name(elf_file), atom.address(elf_file),
         atom.output_section_index, atom.alignment,      atom.size,
     });
-    if (atom.fde_start != atom.fde_end) {
+    if (atom.flags.fde) {
         try writer.writeAll(" : fdes{ ");
-        for (atom.fdes(elf_file), atom.fde_start..) |fde, i| {
+        const extras = atom.extra(elf_file).?;
+        for (atom.fdes(elf_file), extras.fde_start..) |fde, i| {
             try writer.print("{d}", .{i});
             if (!fde.alive) try writer.writeAll("([*])");
-            if (i < atom.fde_end - 1) try writer.writeAll(", ");
+            if (i - extras.fde_start < extras.fde_count - 1) try writer.writeAll(", ");
         }
         try writer.writeAll(" }");
     }
@@ -1042,6 +1096,12 @@ pub const Flags = packed struct {
 
     /// Specifies if the atom has been visited during garbage collection.
     visited: bool = false,
+
+    /// Whether this atom has a range extension thunk.
+    thunk: bool = false,
+
+    /// Whether this atom has FDE records.
+    fde: bool = false,
 };
 
 const x86_64 = struct {
@@ -1232,10 +1292,10 @@ const x86_64 = struct {
 
             .TLSGD => {
                 if (target.flags.has_tlsgd) {
-                    const S_ = @as(i64, @intCast(target.tlsGdAddress(elf_file)));
+                    const S_ = target.tlsGdAddress(elf_file);
                     try cwriter.writeInt(i32, @as(i32, @intCast(S_ + A - P)), .little);
                 } else if (target.flags.has_gottp) {
-                    const S_ = @as(i64, @intCast(target.gotTpAddress(elf_file)));
+                    const S_ = target.gotTpAddress(elf_file);
                     try x86_64.relaxTlsGdToIe(atom, &.{ rel, it.next().? }, @intCast(S_ - P), elf_file, stream);
                 } else {
                     try x86_64.relaxTlsGdToLe(
@@ -1251,13 +1311,13 @@ const x86_64 = struct {
             .TLSLD => {
                 if (elf_file.got.tlsld_index) |entry_index| {
                     const tlsld_entry = elf_file.got.entries.items[entry_index];
-                    const S_ = @as(i64, @intCast(tlsld_entry.address(elf_file)));
+                    const S_ = tlsld_entry.address(elf_file);
                     try cwriter.writeInt(i32, @as(i32, @intCast(S_ + A - P)), .little);
                 } else {
                     try x86_64.relaxTlsLdToLe(
                         atom,
                         &.{ rel, it.next().? },
-                        @as(i32, @intCast(TP - @as(i64, @intCast(elf_file.tlsAddress())))),
+                        @as(i32, @intCast(TP - elf_file.tlsAddress())),
                         elf_file,
                         stream,
                     );
@@ -1266,7 +1326,7 @@ const x86_64 = struct {
 
             .GOTPC32_TLSDESC => {
                 if (target.flags.has_tlsdesc) {
-                    const S_ = @as(i64, @intCast(target.tlsDescAddress(elf_file)));
+                    const S_ = target.tlsDescAddress(elf_file);
                     try cwriter.writeInt(i32, @as(i32, @intCast(S_ + A - P)), .little);
                 } else {
                     x86_64.relaxGotPcTlsDesc(code[r_offset - 3 ..]) catch {
@@ -1290,7 +1350,7 @@ const x86_64 = struct {
 
             .GOTTPOFF => {
                 if (target.flags.has_gottp) {
-                    const S_ = @as(i64, @intCast(target.gotTpAddress(elf_file)));
+                    const S_ = target.gotTpAddress(elf_file);
                     try cwriter.writeInt(i32, @as(i32, @intCast(S_ + A - P)), .little);
                 } else {
                     x86_64.relaxGotTpOff(code[r_offset - 3 ..]);
@@ -1333,9 +1393,18 @@ const x86_64 = struct {
             .@"16" => try cwriter.writeInt(u16, @as(u16, @bitCast(@as(i16, @intCast(S + A)))), .little),
             .@"32" => try cwriter.writeInt(u32, @as(u32, @bitCast(@as(i32, @intCast(S + A)))), .little),
             .@"32S" => try cwriter.writeInt(i32, @as(i32, @intCast(S + A)), .little),
-            .@"64" => try cwriter.writeInt(i64, S + A, .little),
-            .DTPOFF32 => try cwriter.writeInt(i32, @as(i32, @intCast(S + A - DTP)), .little),
-            .DTPOFF64 => try cwriter.writeInt(i64, S + A - DTP, .little),
+            .@"64" => if (atom.debugTombstoneValue(target.*, elf_file)) |value|
+                try cwriter.writeInt(u64, value, .little)
+            else
+                try cwriter.writeInt(i64, S + A, .little),
+            .DTPOFF32 => if (atom.debugTombstoneValue(target.*, elf_file)) |value|
+                try cwriter.writeInt(u64, value, .little)
+            else
+                try cwriter.writeInt(i32, @as(i32, @intCast(S + A - DTP)), .little),
+            .DTPOFF64 => if (atom.debugTombstoneValue(target.*, elf_file)) |value|
+                try cwriter.writeInt(u64, value, .little)
+            else
+                try cwriter.writeInt(i64, S + A - DTP, .little),
             .GOTOFF64 => try cwriter.writeInt(i64, S + A - GOT, .little),
             .GOTPC64 => try cwriter.writeInt(i64, GOT + A, .little),
             .SIZE32 => {
@@ -1717,7 +1786,7 @@ const aarch64 = struct {
                         .object => |x| x.symbols.items[rel.r_sym()],
                         else => unreachable,
                     };
-                    const S_: i64 = @intCast(th.targetAddress(target_index, elf_file));
+                    const S_ = th.targetAddress(target_index, elf_file);
                     break :blk math.cast(i28, S_ + A - P) orelse return error.Overflow;
                 };
                 aarch64_util.writeBranchImm(disp, code);
@@ -1735,16 +1804,12 @@ const aarch64 = struct {
 
             .ADR_PREL_PG_HI21 => {
                 // TODO: check for relaxation of ADRP+ADD
-                const saddr = @as(u64, @intCast(P));
-                const taddr = @as(u64, @intCast(S + A));
-                const pages = @as(u21, @bitCast(try aarch64_util.calcNumberOfPages(saddr, taddr)));
+                const pages = @as(u21, @bitCast(try aarch64_util.calcNumberOfPages(P, S + A)));
                 aarch64_util.writeAdrpInst(pages, code);
             },
 
             .ADR_GOT_PAGE => if (target.flags.has_got) {
-                const saddr = @as(u64, @intCast(P));
-                const taddr = @as(u64, @intCast(G + GOT + A));
-                const pages = @as(u21, @bitCast(try aarch64_util.calcNumberOfPages(saddr, taddr)));
+                const pages = @as(u21, @bitCast(try aarch64_util.calcNumberOfPages(P, G + GOT + A)));
                 aarch64_util.writeAdrpInst(pages, code);
             } else {
                 // TODO: relax
@@ -1799,46 +1864,38 @@ const aarch64 = struct {
             },
 
             .TLSIE_ADR_GOTTPREL_PAGE21 => {
-                const S_: i64 = @intCast(target.gotTpAddress(elf_file));
-                const saddr: u64 = @intCast(P);
-                const taddr: u64 = @intCast(S_ + A);
-                relocs_log.debug("      [{x} => {x}]", .{ P, taddr });
-                const pages: u21 = @bitCast(try aarch64_util.calcNumberOfPages(saddr, taddr));
+                const S_ = target.gotTpAddress(elf_file);
+                relocs_log.debug("      [{x} => {x}]", .{ P, S_ + A });
+                const pages: u21 = @bitCast(try aarch64_util.calcNumberOfPages(P, S_ + A));
                 aarch64_util.writeAdrpInst(pages, code);
             },
 
             .TLSIE_LD64_GOTTPREL_LO12_NC => {
-                const S_: i64 = @intCast(target.gotTpAddress(elf_file));
-                const taddr: u64 = @intCast(S_ + A);
-                relocs_log.debug("      [{x} => {x}]", .{ P, taddr });
-                const offset: u12 = try math.divExact(u12, @truncate(taddr), 8);
+                const S_ = target.gotTpAddress(elf_file);
+                relocs_log.debug("      [{x} => {x}]", .{ P, S_ + A });
+                const offset: u12 = try math.divExact(u12, @truncate(@as(u64, @bitCast(S_ + A))), 8);
                 aarch64_util.writeLoadStoreRegInst(offset, code);
             },
 
             .TLSGD_ADR_PAGE21 => {
-                const S_: i64 = @intCast(target.tlsGdAddress(elf_file));
-                const saddr: u64 = @intCast(P);
-                const taddr: u64 = @intCast(S_ + A);
-                relocs_log.debug("      [{x} => {x}]", .{ P, taddr });
-                const pages: u21 = @bitCast(try aarch64_util.calcNumberOfPages(saddr, taddr));
+                const S_ = target.tlsGdAddress(elf_file);
+                relocs_log.debug("      [{x} => {x}]", .{ P, S_ + A });
+                const pages: u21 = @bitCast(try aarch64_util.calcNumberOfPages(P, S_ + A));
                 aarch64_util.writeAdrpInst(pages, code);
             },
 
             .TLSGD_ADD_LO12_NC => {
-                const S_: i64 = @intCast(target.tlsGdAddress(elf_file));
-                const taddr: u64 = @intCast(S_ + A);
-                relocs_log.debug("      [{x} => {x}]", .{ P, taddr });
-                const offset: u12 = @truncate(taddr);
+                const S_ = target.tlsGdAddress(elf_file);
+                relocs_log.debug("      [{x} => {x}]", .{ P, S_ + A });
+                const offset: u12 = @truncate(@as(u64, @bitCast(S_ + A)));
                 aarch64_util.writeAddImmInst(offset, code);
             },
 
             .TLSDESC_ADR_PAGE21 => {
                 if (target.flags.has_tlsdesc) {
-                    const S_: i64 = @intCast(target.tlsDescAddress(elf_file));
-                    const saddr: u64 = @intCast(P);
-                    const taddr: u64 = @intCast(S_ + A);
-                    relocs_log.debug("      [{x} => {x}]", .{ P, taddr });
-                    const pages: u21 = @bitCast(try aarch64_util.calcNumberOfPages(saddr, taddr));
+                    const S_ = target.tlsDescAddress(elf_file);
+                    relocs_log.debug("      [{x} => {x}]", .{ P, S_ + A });
+                    const pages: u21 = @bitCast(try aarch64_util.calcNumberOfPages(P, S_ + A));
                     aarch64_util.writeAdrpInst(pages, code);
                 } else {
                     relocs_log.debug("      relaxing adrp => nop", .{});
@@ -1848,10 +1905,9 @@ const aarch64 = struct {
 
             .TLSDESC_LD64_LO12 => {
                 if (target.flags.has_tlsdesc) {
-                    const S_: i64 = @intCast(target.tlsDescAddress(elf_file));
-                    const taddr: u64 = @intCast(S_ + A);
-                    relocs_log.debug("      [{x} => {x}]", .{ P, taddr });
-                    const offset: u12 = try math.divExact(u12, @truncate(taddr), 8);
+                    const S_ = target.tlsDescAddress(elf_file);
+                    relocs_log.debug("      [{x} => {x}]", .{ P, S_ + A });
+                    const offset: u12 = try math.divExact(u12, @truncate(@as(u64, @bitCast(S_ + A))), 8);
                     aarch64_util.writeLoadStoreRegInst(offset, code);
                 } else {
                     relocs_log.debug("      relaxing ldr => nop", .{});
@@ -1861,10 +1917,9 @@ const aarch64 = struct {
 
             .TLSDESC_ADD_LO12 => {
                 if (target.flags.has_tlsdesc) {
-                    const S_: i64 = @intCast(target.tlsDescAddress(elf_file));
-                    const taddr: u64 = @intCast(S_ + A);
-                    relocs_log.debug("      [{x} => {x}]", .{ P, taddr });
-                    const offset: u12 = @truncate(taddr);
+                    const S_ = target.tlsDescAddress(elf_file);
+                    relocs_log.debug("      [{x} => {x}]", .{ P, S_ + A });
+                    const offset: u12 = @truncate(@as(u64, @bitCast(S_ + A)));
                     aarch64_util.writeAddImmInst(offset, code);
                 } else {
                     const old_inst = Instruction{
@@ -1909,7 +1964,6 @@ const aarch64 = struct {
     ) !void {
         _ = it;
         _ = code;
-        _ = target;
 
         const r_type: elf.R_AARCH64 = @enumFromInt(rel.r_type());
         const cwriter = stream.writer();
@@ -1919,7 +1973,10 @@ const aarch64 = struct {
         switch (r_type) {
             .NONE => unreachable,
             .ABS32 => try cwriter.writeInt(i32, @as(i32, @intCast(S + A)), .little),
-            .ABS64 => try cwriter.writeInt(i64, S + A, .little),
+            .ABS64 => if (atom.debugTombstoneValue(target.*, elf_file)) |value|
+                try cwriter.writeInt(u64, value, .little)
+            else
+                try cwriter.writeInt(i64, S + A, .little),
             else => try atom.reportUnhandledRelocError(rel, elf_file),
         }
     }
@@ -2044,7 +2101,7 @@ const riscv = struct {
                 const atom_addr = atom.address(elf_file);
                 const pos = it.pos;
                 const pair = while (it.prev()) |pair| {
-                    if (S == atom_addr + pair.r_offset) break pair;
+                    if (S == atom_addr + @as(i64, @intCast(pair.r_offset))) break pair;
                 } else {
                     // TODO: implement searching forward
                     var err = try elf_file.addErrorWithNotes(1);
@@ -2062,10 +2119,10 @@ const riscv = struct {
                     .object => |x| elf_file.symbol(x.symbols.items[pair.r_sym()]),
                     else => unreachable,
                 };
-                const S_ = @as(i64, @intCast(target_.address(.{}, elf_file)));
+                const S_ = target_.address(.{}, elf_file);
                 const A_ = pair.r_addend;
-                const P_ = @as(i64, @intCast(atom_addr + pair.r_offset));
-                const G_ = @as(i64, @intCast(target_.gotAddress(elf_file))) - GOT;
+                const P_ = atom_addr + @as(i64, @intCast(pair.r_offset));
+                const G_ = target_.gotAddress(elf_file) - GOT;
                 const disp = switch (@as(elf.R_RISCV, @enumFromInt(pair.r_type()))) {
                     .PCREL_HI20 => math.cast(i32, S_ + A_ - P_) orelse return error.Overflow,
                     .GOT_HI20 => math.cast(i32, G_ + GOT + A_ - P_) orelse return error.Overflow,
@@ -2093,7 +2150,6 @@ const riscv = struct {
         code: []u8,
         stream: anytype,
     ) !void {
-        _ = target;
         _ = it;
 
         const r_type: elf.R_RISCV = @enumFromInt(rel.r_type());
@@ -2108,7 +2164,10 @@ const riscv = struct {
             .NONE => unreachable,
 
             .@"32" => try cwriter.writeInt(i32, @as(i32, @intCast(S + A)), .little),
-            .@"64" => try cwriter.writeInt(i64, S + A, .little),
+            .@"64" => if (atom.debugTombstoneValue(target.*, elf_file)) |value|
+                try cwriter.writeInt(u64, value, .little)
+            else
+                try cwriter.writeInt(i64, S + A, .little),
 
             .ADD8 => riscv_util.writeAddend(i8, .add, code[r_offset..][0..1], S + A),
             .SUB8 => riscv_util.writeAddend(i8, .sub, code[r_offset..][0..1], S + A),
@@ -2167,6 +2226,23 @@ const RelocsIterator = struct {
     }
 };
 
+pub const Extra = struct {
+    /// Index of the range extension thunk of this atom.
+    thunk: u32 = 0,
+
+    /// Start index of FDEs referencing this atom.
+    fde_start: u32 = 0,
+
+    /// Count of FDEs referencing this atom.
+    fde_count: u32 = 0,
+
+    /// Start index of relocations belonging to this atom.
+    rel_index: u32 = 0,
+
+    /// Count of relocations belonging to this atom.
+    rel_count: u32 = 0,
+};
+
 const std = @import("std");
 const assert = std.debug.assert;
 const elf = std.elf;
diff --git a/src/link/Elf/LinkerDefined.zig b/src/link/Elf/LinkerDefined.zig
index b9fffa1a4a..97edd34791 100644
--- a/src/link/Elf/LinkerDefined.zig
+++ b/src/link/Elf/LinkerDefined.zig
@@ -60,10 +60,10 @@ pub fn updateSymtabSize(self: *LinkerDefined, elf_file: *Elf) !void {
         if (file_ptr.index() != self.index) continue;
         global.flags.output_symtab = true;
         if (global.isLocal(elf_file)) {
-            try global.setOutputSymtabIndex(self.output_symtab_ctx.nlocals, elf_file);
+            try global.addExtra(.{ .symtab = self.output_symtab_ctx.nlocals }, elf_file);
             self.output_symtab_ctx.nlocals += 1;
         } else {
-            try global.setOutputSymtabIndex(self.output_symtab_ctx.nglobals, elf_file);
+            try global.addExtra(.{ .symtab = self.output_symtab_ctx.nglobals }, elf_file);
             self.output_symtab_ctx.nglobals += 1;
         }
         self.output_symtab_ctx.strsize += @as(u32, @intCast(global.name(elf_file).len)) + 1;
diff --git a/src/link/Elf/Object.zig b/src/link/Elf/Object.zig
index d483540aa6..c0e6266bb7 100644
--- a/src/link/Elf/Object.zig
+++ b/src/link/Elf/Object.zig
@@ -15,6 +15,8 @@ comdat_groups: std.ArrayListUnmanaged(Elf.ComdatGroup.Index) = .{},
 comdat_group_data: std.ArrayListUnmanaged(u32) = .{},
 relocs: std.ArrayListUnmanaged(elf.Elf64_Rela) = .{},
 
+merge_sections: std.ArrayListUnmanaged(InputMergeSection.Index) = .{},
+
 fdes: std.ArrayListUnmanaged(Fde) = .{},
 cies: std.ArrayListUnmanaged(Cie) = .{},
 eh_frame_data: std.ArrayListUnmanaged(u8) = .{},
@@ -51,6 +53,7 @@ pub fn deinit(self: *Object, allocator: Allocator) void {
     self.fdes.deinit(allocator);
     self.cies.deinit(allocator);
     self.eh_frame_data.deinit(allocator);
+    self.merge_sections.deinit(allocator);
 }
 
 pub fn parse(self: *Object, elf_file: *Elf) !void {
@@ -242,11 +245,12 @@ fn initAtoms(self: *Object, allocator: Allocator, handle: std.fs.File, elf_file:
                 const relocs = try self.preadRelocsAlloc(allocator, handle, @intCast(i));
                 defer allocator.free(relocs);
                 atom.relocs_section_index = @intCast(i);
-                atom.rel_index = @intCast(self.relocs.items.len);
-                atom.rel_num = @intCast(relocs.len);
+                const rel_index: u32 = @intCast(self.relocs.items.len);
+                const rel_count: u32 = @intCast(relocs.len);
+                try atom.addExtra(.{ .rel_index = rel_index, .rel_count = rel_count }, elf_file);
                 try self.relocs.appendUnalignedSlice(allocator, relocs);
                 if (elf_file.getTarget().cpu.arch == .riscv64) {
-                    sortRelocs(self.relocs.items[atom.rel_index..][0..atom.rel_num]);
+                    sortRelocs(self.relocs.items[rel_index..][0..rel_count]);
                 }
             }
         },
@@ -279,8 +283,7 @@ fn initOutputSection(self: Object, elf_file: *Elf, shdr: elf.Elf64_Shdr) error{O
     const name = blk: {
         const name = self.getString(shdr.sh_name);
         if (elf_file.base.isRelocatable()) break :blk name;
-        if (shdr.sh_flags & elf.SHF_MERGE != 0 and shdr.sh_flags & elf.SHF_STRINGS == 0)
-            break :blk name; // TODO: consider dropping SHF_STRINGS once ICF is implemented
+        if (shdr.sh_flags & elf.SHF_MERGE != 0) break :blk name;
         const sh_name_prefixes: []const [:0]const u8 = &.{
             ".text",       ".data.rel.ro", ".data", ".rodata", ".bss.rel.ro",       ".bss",
             ".init_array", ".fini_array",  ".tbss", ".tdata",  ".gcc_except_table", ".ctors",
@@ -334,7 +337,6 @@ fn skipShdr(self: *Object, index: u32, elf_file: *Elf) bool {
     const name = self.getString(shdr.sh_name);
     const ignore = blk: {
         if (mem.startsWith(u8, name, ".note")) break :blk true;
-        if (mem.startsWith(u8, name, ".comment")) break :blk true;
         if (mem.startsWith(u8, name, ".llvm_addrsig")) break :blk true;
         if (mem.startsWith(u8, name, ".riscv.attributes")) break :blk true; // TODO: riscv attributes
         if (comp.config.debug_format == .strip and shdr.sh_flags & elf.SHF_ALLOC == 0 and
@@ -353,7 +355,7 @@ fn initSymtab(self: *Object, allocator: Allocator, elf_file: *Elf) !void {
         const index = try elf_file.addSymbol();
         self.symbols.appendAssumeCapacity(index);
         const sym_ptr = elf_file.symbol(index);
-        sym_ptr.value = sym.st_value;
+        sym_ptr.value = @intCast(sym.st_value);
         sym_ptr.name_offset = sym.st_name;
         sym_ptr.esym_index = @as(u32, @intCast(i));
         sym_ptr.atom_index = if (sym.st_shndx == elf.SHN_ABS) 0 else self.atoms.items[sym.st_shndx];
@@ -445,13 +447,14 @@ fn parseEhFrame(self: *Object, allocator: Allocator, handle: std.fs.File, shndx:
     while (i < self.fdes.items.len) {
         const fde = self.fdes.items[i];
         const atom = fde.atom(elf_file);
-        atom.fde_start = i;
+        const start = i;
         i += 1;
         while (i < self.fdes.items.len) : (i += 1) {
             const next_fde = self.fdes.items[i];
             if (atom.atom_index != next_fde.atom(elf_file).atom_index) break;
         }
-        atom.fde_end = i;
+        try atom.addExtra(.{ .fde_start = start, .fde_count = i - start }, elf_file);
+        atom.flags.fde = true;
     }
 }
 
@@ -545,7 +548,7 @@ pub fn resolveSymbols(self: *Object, elf_file: *Elf) void {
                 elf.SHN_ABS, elf.SHN_COMMON => 0,
                 else => self.atoms.items[esym.st_shndx],
             };
-            global.value = esym.st_value;
+            global.value = @intCast(esym.st_value);
             global.atom_index = atom_index;
             global.esym_index = esym_index;
             global.file_index = self.index;
@@ -657,6 +660,178 @@ pub fn checkDuplicates(self: *Object, dupes: anytype, elf_file: *Elf) error{OutO
     }
 }
 
+pub fn initMergeSections(self: *Object, elf_file: *Elf) !void {
+    const gpa = elf_file.base.comp.gpa;
+
+    try self.merge_sections.resize(gpa, self.shdrs.items.len);
+    @memset(self.merge_sections.items, 0);
+
+    for (self.shdrs.items, 0..) |shdr, shndx| {
+        if (shdr.sh_flags & elf.SHF_MERGE == 0) continue;
+
+        const atom_index = self.atoms.items[shndx];
+        const atom_ptr = elf_file.atom(atom_index) orelse continue;
+        if (!atom_ptr.flags.alive) continue;
+        if (atom_ptr.relocs(elf_file).len > 0) continue;
+
+        const imsec_idx = try elf_file.addInputMergeSection();
+        const imsec = elf_file.inputMergeSection(imsec_idx).?;
+        self.merge_sections.items[shndx] = imsec_idx;
+
+        imsec.merge_section_index = try elf_file.getOrCreateMergeSection(atom_ptr.name(elf_file), shdr.sh_flags, shdr.sh_type);
+        imsec.atom_index = atom_index;
+
+        const data = try self.codeDecompressAlloc(elf_file, atom_index);
+        defer gpa.free(data);
+
+        if (shdr.sh_flags & elf.SHF_STRINGS != 0) {
+            const sh_entsize: u32 = switch (shdr.sh_entsize) {
+                // According to mold's source code, GHC emits MS sections with sh_entsize = 0.
+                // This actually can also happen for output created with `-r` mode.
+                0 => 1,
+                else => |x| @intCast(x),
+            };
+
+            const isNull = struct {
+                fn isNull(slice: []u8) bool {
+                    for (slice) |x| if (x != 0) return false;
+                    return true;
+                }
+            }.isNull;
+
+            var start: u32 = 0;
+            while (start < data.len) {
+                var end = start;
+                while (end < data.len - sh_entsize and !isNull(data[end .. end + sh_entsize])) : (end += sh_entsize) {}
+                if (!isNull(data[end .. end + sh_entsize])) {
+                    var err = try elf_file.addErrorWithNotes(1);
+                    try err.addMsg(elf_file, "string not null terminated", .{});
+                    try err.addNote(elf_file, "in {}:{s}", .{ self.fmtPath(), atom_ptr.name(elf_file) });
+                    return error.MalformedObject;
+                }
+                end += sh_entsize;
+                const string = data[start..end];
+                try imsec.insert(gpa, string);
+                try imsec.offsets.append(gpa, start);
+                start = end;
+            }
+        } else {
+            const sh_entsize: u32 = @intCast(shdr.sh_entsize);
+            if (sh_entsize == 0) continue; // Malformed, don't split but don't error out
+            if (shdr.sh_size % sh_entsize != 0) {
+                var err = try elf_file.addErrorWithNotes(1);
+                try err.addMsg(elf_file, "size not a multiple of sh_entsize", .{});
+                try err.addNote(elf_file, "in {}:{s}", .{ self.fmtPath(), atom_ptr.name(elf_file) });
+                return error.MalformedObject;
+            }
+
+            var pos: u32 = 0;
+            while (pos < data.len) : (pos += sh_entsize) {
+                const string = data.ptr[pos..][0..sh_entsize];
+                try imsec.insert(gpa, string);
+                try imsec.offsets.append(gpa, pos);
+            }
+        }
+
+        atom_ptr.flags.alive = false;
+    }
+}
+
+pub fn resolveMergeSubsections(self: *Object, elf_file: *Elf) !void {
+    const gpa = elf_file.base.comp.gpa;
+
+    for (self.merge_sections.items) |index| {
+        const imsec = elf_file.inputMergeSection(index) orelse continue;
+        if (imsec.offsets.items.len == 0) continue;
+        const msec = elf_file.mergeSection(imsec.merge_section_index);
+        const atom_ptr = elf_file.atom(imsec.atom_index).?;
+        const isec = atom_ptr.inputShdr(elf_file);
+
+        try imsec.subsections.resize(gpa, imsec.strings.items.len);
+
+        for (imsec.strings.items, imsec.subsections.items) |str, *imsec_msub| {
+            const string = imsec.bytes.items[str.pos..][0..str.len];
+            const res = try msec.insert(gpa, string);
+            if (!res.found_existing) {
+                const msub_index = try elf_file.addMergeSubsection();
+                const msub = elf_file.mergeSubsection(msub_index);
+                msub.merge_section_index = imsec.merge_section_index;
+                msub.string_index = res.key.pos;
+                msub.alignment = atom_ptr.alignment;
+                msub.size = res.key.len;
+                msub.entsize = math.cast(u32, isec.sh_entsize) orelse return error.Overflow;
+                msub.alive = !elf_file.base.gc_sections or isec.sh_flags & elf.SHF_ALLOC == 0;
+                res.sub.* = msub_index;
+            }
+            imsec_msub.* = res.sub.*;
+        }
+
+        imsec.clearAndFree(gpa);
+    }
+
+    for (self.symtab.items, 0..) |*esym, idx| {
+        const sym_index = self.symbols.items[idx];
+        const sym = elf_file.symbol(sym_index);
+
+        if (esym.st_shndx == elf.SHN_COMMON or esym.st_shndx == elf.SHN_UNDEF or esym.st_shndx == elf.SHN_ABS) continue;
+
+        const imsec_index = self.merge_sections.items[esym.st_shndx];
+        const imsec = elf_file.inputMergeSection(imsec_index) orelse continue;
+        if (imsec.offsets.items.len == 0) continue;
+        const msub_index, const offset = imsec.findSubsection(@intCast(esym.st_value)) orelse {
+            var err = try elf_file.addErrorWithNotes(2);
+            try err.addMsg(elf_file, "invalid symbol value: {x}", .{esym.st_value});
+            try err.addNote(elf_file, "for symbol {s}", .{sym.name(elf_file)});
+            try err.addNote(elf_file, "in {}", .{self.fmtPath()});
+            return error.MalformedObject;
+        };
+
+        try sym.addExtra(.{ .subsection = msub_index }, elf_file);
+        sym.flags.merge_subsection = true;
+        sym.value = offset;
+    }
+
+    for (self.atoms.items) |atom_index| {
+        const atom_ptr = elf_file.atom(atom_index) orelse continue;
+        if (!atom_ptr.flags.alive) continue;
+        const extras = atom_ptr.extra(elf_file) orelse continue;
+        const relocs = self.relocs.items[extras.rel_index..][0..extras.rel_count];
+        for (relocs) |*rel| {
+            const esym = self.symtab.items[rel.r_sym()];
+            if (esym.st_type() != elf.STT_SECTION) continue;
+
+            const imsec_index = self.merge_sections.items[esym.st_shndx];
+            const imsec = elf_file.inputMergeSection(imsec_index) orelse continue;
+            if (imsec.offsets.items.len == 0) continue;
+            const msub_index, const offset = imsec.findSubsection(@intCast(@as(i64, @intCast(esym.st_value)) + rel.r_addend)) orelse {
+                var err = try elf_file.addErrorWithNotes(1);
+                try err.addMsg(elf_file, "invalid relocation at offset 0x{x}", .{rel.r_offset});
+                try err.addNote(elf_file, "in {}:{s}", .{ self.fmtPath(), atom_ptr.name(elf_file) });
+                return error.MalformedObject;
+            };
+            const msub = elf_file.mergeSubsection(msub_index);
+            const msec = msub.mergeSection(elf_file);
+
+            const out_sym_idx: u64 = @intCast(self.symbols.items.len);
+            try self.symbols.ensureUnusedCapacity(gpa, 1);
+            const name = try std.fmt.allocPrint(gpa, "{s}$subsection{d}", .{ msec.name(elf_file), msub_index });
+            defer gpa.free(name);
+            const sym_index = try elf_file.addSymbol();
+            const sym = elf_file.symbol(sym_index);
+            sym.* = .{
+                .value = @bitCast(@as(i64, @intCast(offset)) - rel.r_addend),
+                .name_offset = try self.addString(gpa, name),
+                .esym_index = rel.r_sym(),
+                .file_index = self.index,
+            };
+            try sym.addExtra(.{ .subsection = msub_index }, elf_file);
+            sym.flags.merge_subsection = true;
+            self.symbols.addOneAssumeCapacity().* = sym_index;
+            rel.r_info = (out_sym_idx << 32) | rel.r_type();
+        }
+    }
+}
+
 /// We will create dummy shdrs per each resolved common symbols to make it
 /// play nicely with the rest of the system.
 pub fn convertCommonSymbols(self: *Object, elf_file: *Elf) !void {
@@ -747,6 +922,11 @@ pub fn addAtomsToOutputSections(self: *Object, elf_file: *Elf) !void {
 
     for (self.locals()) |local_index| {
         const local = elf_file.symbol(local_index);
+        if (local.mergeSubsection(elf_file)) |msub| {
+            if (!msub.alive) continue;
+            local.output_section_index = msub.mergeSection(elf_file).output_section_index;
+            continue;
+        }
         const atom = local.atom(elf_file) orelse continue;
         if (!atom.flags.alive) continue;
         local.output_section_index = atom.output_section_index;
@@ -754,11 +934,23 @@ pub fn addAtomsToOutputSections(self: *Object, elf_file: *Elf) !void {
 
     for (self.globals()) |global_index| {
         const global = elf_file.symbol(global_index);
+        if (global.file(elf_file).?.index() != self.index) continue;
+        if (global.mergeSubsection(elf_file)) |msub| {
+            if (!msub.alive) continue;
+            global.output_section_index = msub.mergeSection(elf_file).output_section_index;
+            continue;
+        }
         const atom = global.atom(elf_file) orelse continue;
         if (!atom.flags.alive) continue;
-        if (global.file(elf_file).?.index() != self.index) continue;
         global.output_section_index = atom.output_section_index;
     }
+
+    for (self.symbols.items[self.symtab.items.len..]) |local_index| {
+        const local = elf_file.symbol(local_index);
+        const msub = local.mergeSubsection(elf_file).?;
+        if (!msub.alive) continue;
+        local.output_section_index = msub.mergeSection(elf_file).output_section_index;
+    }
 }
 
 pub fn initRelaSections(self: Object, elf_file: *Elf) !void {
@@ -817,13 +1009,15 @@ pub fn updateArSymtab(self: Object, ar_symtab: *Archive.ArSymtab, elf_file: *Elf
 }
 
 pub fn updateArSize(self: *Object, elf_file: *Elf) !void {
-    const handle = elf_file.fileHandle(self.file_handle);
-    const size = (try handle.stat()).size;
-    self.output_ar_state.size = size;
+    self.output_ar_state.size = if (self.archive) |ar| ar.size else size: {
+        const handle = elf_file.fileHandle(self.file_handle);
+        break :size (try handle.stat()).size;
+    };
 }
 
 pub fn writeAr(self: Object, elf_file: *Elf, writer: anytype) !void {
     const size = std.math.cast(usize, self.output_ar_state.size) orelse return error.Overflow;
+    const offset: u64 = if (self.archive) |ar| ar.offset else 0;
     const name = self.path;
     const hdr = Archive.setArHdr(.{
         .name = if (name.len <= Archive.max_member_name_len)
@@ -837,15 +1031,23 @@ pub fn writeAr(self: Object, elf_file: *Elf, writer: anytype) !void {
     const gpa = elf_file.base.comp.gpa;
     const data = try gpa.alloc(u8, size);
     defer gpa.free(data);
-    const amt = try handle.preadAll(data, 0);
+    const amt = try handle.preadAll(data, offset);
     if (amt != size) return error.InputOutput;
     try writer.writeAll(data);
 }
 
 pub fn updateSymtabSize(self: *Object, elf_file: *Elf) !void {
+    const isAlive = struct {
+        fn isAlive(sym: *const Symbol, ctx: *Elf) bool {
+            if (sym.mergeSubsection(ctx)) |msub| return msub.alive;
+            if (sym.atom(ctx)) |atom_ptr| return atom_ptr.flags.alive;
+            return true;
+        }
+    }.isAlive;
+
     for (self.locals()) |local_index| {
         const local = elf_file.symbol(local_index);
-        if (local.atom(elf_file)) |atom| if (!atom.flags.alive) continue;
+        if (!isAlive(local, elf_file)) continue;
         const esym = local.elfSym(elf_file);
         switch (esym.st_type()) {
             elf.STT_SECTION => continue,
@@ -853,7 +1055,7 @@ pub fn updateSymtabSize(self: *Object, elf_file: *Elf) !void {
             else => {},
         }
         local.flags.output_symtab = true;
-        try local.setOutputSymtabIndex(self.output_symtab_ctx.nlocals, elf_file);
+        try local.addExtra(.{ .symtab = self.output_symtab_ctx.nlocals }, elf_file);
         self.output_symtab_ctx.nlocals += 1;
         self.output_symtab_ctx.strsize += @as(u32, @intCast(local.name(elf_file).len)) + 1;
     }
@@ -862,13 +1064,13 @@ pub fn updateSymtabSize(self: *Object, elf_file: *Elf) !void {
         const global = elf_file.symbol(global_index);
         const file_ptr = global.file(elf_file) orelse continue;
         if (file_ptr.index() != self.index) continue;
-        if (global.atom(elf_file)) |atom| if (!atom.flags.alive) continue;
+        if (!isAlive(global, elf_file)) continue;
         global.flags.output_symtab = true;
         if (global.isLocal(elf_file)) {
-            try global.setOutputSymtabIndex(self.output_symtab_ctx.nlocals, elf_file);
+            try global.addExtra(.{ .symtab = self.output_symtab_ctx.nlocals }, elf_file);
             self.output_symtab_ctx.nlocals += 1;
         } else {
-            try global.setOutputSymtabIndex(self.output_symtab_ctx.nglobals, elf_file);
+            try global.addExtra(.{ .symtab = self.output_symtab_ctx.nglobals }, elf_file);
             self.output_symtab_ctx.nglobals += 1;
         }
         self.output_symtab_ctx.strsize += @as(u32, @intCast(global.name(elf_file).len)) + 1;
@@ -902,14 +1104,16 @@ pub fn writeSymtab(self: Object, elf_file: *Elf) void {
 
 pub fn locals(self: Object) []const Symbol.Index {
     if (self.symbols.items.len == 0) return &[0]Symbol.Index{};
-    const end = self.first_global orelse self.symbols.items.len;
+    assert(self.symbols.items.len >= self.symtab.items.len);
+    const end = self.first_global orelse self.symtab.items.len;
     return self.symbols.items[0..end];
 }
 
 pub fn globals(self: Object) []const Symbol.Index {
     if (self.symbols.items.len == 0) return &[0]Symbol.Index{};
-    const start = self.first_global orelse self.symbols.items.len;
-    return self.symbols.items[start..];
+    assert(self.symbols.items.len >= self.symtab.items.len);
+    const start = self.first_global orelse self.symtab.items.len;
+    return self.symbols.items[start..self.symtab.items.len];
 }
 
 /// Returns atom's code and optionally uncompresses data if required (for compressed sections).
@@ -954,6 +1158,14 @@ pub fn getString(self: Object, off: u32) [:0]const u8 {
     return mem.sliceTo(@as([*:0]const u8, @ptrCast(self.strtab.items.ptr + off)), 0);
 }
 
+fn addString(self: *Object, allocator: Allocator, str: []const u8) !u32 {
+    const off: u32 = @intCast(self.strtab.items.len);
+    try self.strtab.ensureUnusedCapacity(allocator, str.len + 1);
+    self.strtab.appendSliceAssumeCapacity(str);
+    self.strtab.appendAssumeCapacity(0);
+    return off;
+}
+
 /// Caller owns the memory.
 fn preadShdrContentsAlloc(self: Object, allocator: Allocator, handle: std.fs.File, index: u32) ![]u8 {
     assert(index < self.shdrs.items.len);
@@ -1139,6 +1351,7 @@ fn formatPath(
 const InArchive = struct {
     path: []const u8,
     offset: u64,
+    size: u32,
 };
 
 const Object = @This();
@@ -1159,5 +1372,6 @@ const Cie = eh_frame.Cie;
 const Elf = @import("../Elf.zig");
 const Fde = eh_frame.Fde;
 const File = @import("file.zig").File;
+const InputMergeSection = @import("merge_section.zig").InputMergeSection;
 const Symbol = @import("Symbol.zig");
 const Alignment = Atom.Alignment;
diff --git a/src/link/Elf/SharedObject.zig b/src/link/Elf/SharedObject.zig
index d40367f304..2ec5b211e8 100644
--- a/src/link/Elf/SharedObject.zig
+++ b/src/link/Elf/SharedObject.zig
@@ -231,7 +231,7 @@ pub fn resolveSymbols(self: *SharedObject, elf_file: *Elf) void {
 
         const global = elf_file.symbol(index);
         if (self.asFile().symbolRank(this_sym, false) < global.symbolRank(elf_file)) {
-            global.value = this_sym.st_value;
+            global.value = @intCast(this_sym.st_value);
             global.atom_index = 0;
             global.esym_index = esym_index;
             global.version_index = self.versyms.items[esym_index];
@@ -269,7 +269,7 @@ pub fn updateSymtabSize(self: *SharedObject, elf_file: *Elf) !void {
         if (file_ptr.index() != self.index) continue;
         if (global.isLocal(elf_file)) continue;
         global.flags.output_symtab = true;
-        try global.setOutputSymtabIndex(self.output_symtab_ctx.nglobals, elf_file);
+        try global.addExtra(.{ .symtab = self.output_symtab_ctx.nglobals }, elf_file);
         self.output_symtab_ctx.nglobals += 1;
         self.output_symtab_ctx.strsize += @as(u32, @intCast(global.name(elf_file).len)) + 1;
     }
diff --git a/src/link/Elf/Symbol.zig b/src/link/Elf/Symbol.zig
index 9db17f2f4f..21061f036b 100644
--- a/src/link/Elf/Symbol.zig
+++ b/src/link/Elf/Symbol.zig
@@ -1,7 +1,7 @@
 //! Represents a defined symbol.
 
 /// Allocated address value of this symbol.
-value: u64 = 0,
+value: i64 = 0,
 
 /// Offset into the linker's string table.
 name_offset: u32 = 0,
@@ -14,7 +14,7 @@ file_index: File.Index = 0,
 /// Use `atom` to get the pointer to the atom.
 atom_index: Atom.Index = 0,
 
-/// Assigned output section index for this atom.
+/// Assigned output section index for this symbol.
 output_section_index: u32 = 0,
 
 /// Index of the source symbol this symbol references.
@@ -33,7 +33,8 @@ extra_index: u32 = 0,
 pub fn isAbs(symbol: Symbol, elf_file: *Elf) bool {
     const file_ptr = symbol.file(elf_file).?;
     if (file_ptr == .shared_object) return symbol.elfSym(elf_file).st_shndx == elf.SHN_ABS;
-    return !symbol.flags.import and symbol.atom(elf_file) == null and symbol.outputShndx() == null and
+    return !symbol.flags.import and symbol.atom(elf_file) == null and
+        symbol.mergeSubsection(elf_file) == null and symbol.outputShndx() == null and
         file_ptr != .linker_defined;
 }
 
@@ -70,6 +71,12 @@ pub fn atom(symbol: Symbol, elf_file: *Elf) ?*Atom {
     return elf_file.atom(symbol.atom_index);
 }
 
+pub fn mergeSubsection(symbol: Symbol, elf_file: *Elf) ?*MergeSubsection {
+    if (!symbol.flags.merge_subsection) return null;
+    const extras = symbol.extra(elf_file).?;
+    return elf_file.mergeSubsection(extras.subsection);
+}
+
 pub fn file(symbol: Symbol, elf_file: *Elf) ?File {
     return elf_file.file(symbol.file_index);
 }
@@ -92,7 +99,11 @@ pub fn symbolRank(symbol: Symbol, elf_file: *Elf) u32 {
     return file_ptr.symbolRank(sym, in_archive);
 }
 
-pub fn address(symbol: Symbol, opts: struct { plt: bool = true }, elf_file: *Elf) u64 {
+pub fn address(symbol: Symbol, opts: struct { plt: bool = true }, elf_file: *Elf) i64 {
+    if (symbol.mergeSubsection(elf_file)) |msub| {
+        if (!msub.alive) return 0;
+        return msub.address(elf_file) + symbol.value;
+    }
     if (symbol.flags.has_copy_rel) {
         return symbol.copyRelAddress(elf_file);
     }
@@ -108,19 +119,23 @@ pub fn address(symbol: Symbol, opts: struct { plt: bool = true }, elf_file: *Elf
         if (!atom_ptr.flags.alive) {
             if (mem.eql(u8, atom_ptr.name(elf_file), ".eh_frame")) {
                 const sym_name = symbol.name(elf_file);
+                const sh_addr, const sh_size = blk: {
+                    const shndx = elf_file.eh_frame_section_index orelse break :blk .{ 0, 0 };
+                    const shdr = elf_file.shdrs.items[shndx];
+                    break :blk .{ shdr.sh_addr, shdr.sh_size };
+                };
                 if (mem.startsWith(u8, sym_name, "__EH_FRAME_BEGIN__") or
                     mem.startsWith(u8, sym_name, "__EH_FRAME_LIST__") or
                     mem.startsWith(u8, sym_name, ".eh_frame_seg") or
                     symbol.elfSym(elf_file).st_type() == elf.STT_SECTION)
                 {
-                    return elf_file.shdrs.items[elf_file.eh_frame_section_index.?].sh_addr;
+                    return @intCast(sh_addr);
                 }
 
                 if (mem.startsWith(u8, sym_name, "__FRAME_END__") or
                     mem.startsWith(u8, sym_name, "__EH_FRAME_LIST_END__"))
                 {
-                    const shdr = elf_file.shdrs.items[elf_file.eh_frame_section_index.?];
-                    return shdr.sh_addr + shdr.sh_size;
+                    return @intCast(sh_addr + sh_size);
                 }
 
                 // TODO I think we potentially should error here
@@ -143,65 +158,57 @@ pub fn outputSymtabIndex(symbol: Symbol, elf_file: *Elf) ?u32 {
     return if (symbol.isLocal(elf_file)) idx + symtab_ctx.ilocal else idx + symtab_ctx.iglobal;
 }
 
-pub fn setOutputSymtabIndex(symbol: *Symbol, index: u32, elf_file: *Elf) !void {
-    if (symbol.extra(elf_file)) |extras| {
-        var new_extras = extras;
-        new_extras.symtab = index;
-        symbol.setExtra(new_extras, elf_file);
-    } else try symbol.addExtra(.{ .symtab = index }, elf_file);
-}
-
-pub fn gotAddress(symbol: Symbol, elf_file: *Elf) u64 {
+pub fn gotAddress(symbol: Symbol, elf_file: *Elf) i64 {
     if (!symbol.flags.has_got) return 0;
     const extras = symbol.extra(elf_file).?;
     const entry = elf_file.got.entries.items[extras.got];
     return entry.address(elf_file);
 }
 
-pub fn pltGotAddress(symbol: Symbol, elf_file: *Elf) u64 {
+pub fn pltGotAddress(symbol: Symbol, elf_file: *Elf) i64 {
     if (!(symbol.flags.has_plt and symbol.flags.has_got)) return 0;
     const extras = symbol.extra(elf_file).?;
     const shdr = elf_file.shdrs.items[elf_file.plt_got_section_index.?];
     const cpu_arch = elf_file.getTarget().cpu.arch;
-    return shdr.sh_addr + extras.plt_got * PltGotSection.entrySize(cpu_arch);
+    return @intCast(shdr.sh_addr + extras.plt_got * PltGotSection.entrySize(cpu_arch));
 }
 
-pub fn pltAddress(symbol: Symbol, elf_file: *Elf) u64 {
+pub fn pltAddress(symbol: Symbol, elf_file: *Elf) i64 {
     if (!symbol.flags.has_plt) return 0;
     const extras = symbol.extra(elf_file).?;
     const shdr = elf_file.shdrs.items[elf_file.plt_section_index.?];
     const cpu_arch = elf_file.getTarget().cpu.arch;
-    return shdr.sh_addr + extras.plt * PltSection.entrySize(cpu_arch) + PltSection.preambleSize(cpu_arch);
+    return @intCast(shdr.sh_addr + extras.plt * PltSection.entrySize(cpu_arch) + PltSection.preambleSize(cpu_arch));
 }
 
-pub fn gotPltAddress(symbol: Symbol, elf_file: *Elf) u64 {
+pub fn gotPltAddress(symbol: Symbol, elf_file: *Elf) i64 {
     if (!symbol.flags.has_plt) return 0;
     const extras = symbol.extra(elf_file).?;
     const shdr = elf_file.shdrs.items[elf_file.got_plt_section_index.?];
-    return shdr.sh_addr + extras.plt * 8 + GotPltSection.preamble_size;
+    return @intCast(shdr.sh_addr + extras.plt * 8 + GotPltSection.preamble_size);
 }
 
-pub fn copyRelAddress(symbol: Symbol, elf_file: *Elf) u64 {
+pub fn copyRelAddress(symbol: Symbol, elf_file: *Elf) i64 {
     if (!symbol.flags.has_copy_rel) return 0;
     const shdr = elf_file.shdrs.items[elf_file.copy_rel_section_index.?];
-    return shdr.sh_addr + symbol.value;
+    return @as(i64, @intCast(shdr.sh_addr)) + symbol.value;
 }
 
-pub fn tlsGdAddress(symbol: Symbol, elf_file: *Elf) u64 {
+pub fn tlsGdAddress(symbol: Symbol, elf_file: *Elf) i64 {
     if (!symbol.flags.has_tlsgd) return 0;
     const extras = symbol.extra(elf_file).?;
     const entry = elf_file.got.entries.items[extras.tlsgd];
     return entry.address(elf_file);
 }
 
-pub fn gotTpAddress(symbol: Symbol, elf_file: *Elf) u64 {
+pub fn gotTpAddress(symbol: Symbol, elf_file: *Elf) i64 {
     if (!symbol.flags.has_gottp) return 0;
     const extras = symbol.extra(elf_file).?;
     const entry = elf_file.got.entries.items[extras.gottp];
     return entry.address(elf_file);
 }
 
-pub fn tlsDescAddress(symbol: Symbol, elf_file: *Elf) u64 {
+pub fn tlsDescAddress(symbol: Symbol, elf_file: *Elf) i64 {
     if (!symbol.flags.has_tlsdesc) return 0;
     const extras = symbol.extra(elf_file).?;
     const entry = elf_file.got.entries.items[extras.tlsdesc];
@@ -221,7 +228,7 @@ pub fn getOrCreateZigGotEntry(symbol: *Symbol, symbol_index: Index, elf_file: *E
     return .{ .found_existing = false, .index = index };
 }
 
-pub fn zigGotAddress(symbol: Symbol, elf_file: *Elf) u64 {
+pub fn zigGotAddress(symbol: Symbol, elf_file: *Elf) i64 {
     if (!symbol.flags.has_zig_got) return 0;
     const extras = symbol.extra(elf_file).?;
     return elf_file.zig_got.entryAddress(extras.zig_got, elf_file);
@@ -240,8 +247,31 @@ pub fn dsoAlignment(symbol: Symbol, elf_file: *Elf) !u64 {
         @min(alignment, try std.math.powi(u64, 2, @ctz(esym.st_value)));
 }
 
-pub fn addExtra(symbol: *Symbol, extras: Extra, elf_file: *Elf) !void {
-    symbol.extra_index = try elf_file.addSymbolExtra(extras);
+const AddExtraOpts = struct {
+    got: ?u32 = null,
+    plt: ?u32 = null,
+    plt_got: ?u32 = null,
+    dynamic: ?u32 = null,
+    symtab: ?u32 = null,
+    copy_rel: ?u32 = null,
+    tlsgd: ?u32 = null,
+    gottp: ?u32 = null,
+    tlsdesc: ?u32 = null,
+    zig_got: ?u32 = null,
+    subsection: ?u32 = null,
+};
+
+pub fn addExtra(symbol: *Symbol, opts: AddExtraOpts, elf_file: *Elf) !void {
+    if (symbol.extra(elf_file) == null) {
+        symbol.extra_index = try elf_file.addSymbolExtra(.{});
+    }
+    var extras = symbol.extra(elf_file).?;
+    inline for (@typeInfo(@TypeOf(opts)).Struct.fields) |field| {
+        if (@field(opts, field.name)) |x| {
+            @field(extras, field.name) = x;
+        }
+    }
+    symbol.setExtra(extras, elf_file);
 }
 
 pub fn extra(symbol: Symbol, elf_file: *Elf) ?Extra {
@@ -266,6 +296,7 @@ pub fn setOutputSym(symbol: Symbol, elf_file: *Elf, out: *elf.Elf64_Sym) void {
         if (symbol.flags.has_copy_rel) break :blk @intCast(elf_file.copy_rel_section_index.?);
         if (file_ptr == .shared_object or esym.st_shndx == elf.SHN_UNDEF) break :blk elf.SHN_UNDEF;
         if (elf_file.base.isRelocatable() and esym.st_shndx == elf.SHN_COMMON) break :blk elf.SHN_COMMON;
+        if (symbol.mergeSubsection(elf_file)) |msub| break :blk @intCast(msub.mergeSection(elf_file).output_section_index);
         if (symbol.atom(elf_file) == null and file_ptr != .linker_defined) break :blk elf.SHN_ABS;
         break :blk @intCast(symbol.outputShndx() orelse elf.SHN_UNDEF);
     };
@@ -284,7 +315,7 @@ pub fn setOutputSym(symbol: Symbol, elf_file: *Elf, out: *elf.Elf64_Sym) void {
     out.st_info = (st_bind << 4) | st_type;
     out.st_other = esym.st_other;
     out.st_shndx = st_shndx;
-    out.st_value = st_value;
+    out.st_value = @intCast(st_value);
     out.st_size = esym.st_size;
 }
 
@@ -436,6 +467,9 @@ pub const Flags = packed struct {
     /// TODO this is really not needed if only we operated on esyms between
     /// codegen and ZigObject.
     is_tls: bool = false,
+
+    /// Whether the symbol is a merge subsection.
+    merge_subsection: bool = false,
 };
 
 pub const Extra = struct {
@@ -449,6 +483,7 @@ pub const Extra = struct {
     gottp: u32 = 0,
     tlsdesc: u32 = 0,
     zig_got: u32 = 0,
+    subsection: u32 = 0,
 };
 
 pub const Index = u32;
@@ -465,6 +500,7 @@ const File = @import("file.zig").File;
 const GotSection = synthetic_sections.GotSection;
 const GotPltSection = synthetic_sections.GotPltSection;
 const LinkerDefined = @import("LinkerDefined.zig");
+const MergeSubsection = @import("merge_section.zig").MergeSubsection;
 const Object = @import("Object.zig");
 const PltSection = synthetic_sections.PltSection;
 const PltGotSection = synthetic_sections.PltGotSection;
diff --git a/src/link/Elf/ZigObject.zig b/src/link/Elf/ZigObject.zig
index f65ef43eac..98af014068 100644
--- a/src/link/Elf/ZigObject.zig
+++ b/src/link/Elf/ZigObject.zig
@@ -343,7 +343,7 @@ pub fn resolveSymbols(self: *ZigObject, elf_file: *Elf) void {
                 atom.outputShndx().?
             else
                 elf.SHN_UNDEF;
-            global.value = esym.st_value;
+            global.value = @intCast(esym.st_value);
             global.atom_index = atom_index;
             global.esym_index = esym_index;
             global.file_index = self.index;
@@ -566,7 +566,7 @@ pub fn updateSymtabSize(self: *ZigObject, elf_file: *Elf) !void {
             else => {},
         }
         local.flags.output_symtab = true;
-        try local.setOutputSymtabIndex(self.output_symtab_ctx.nlocals, elf_file);
+        try local.addExtra(.{ .symtab = self.output_symtab_ctx.nlocals }, elf_file);
         self.output_symtab_ctx.nlocals += 1;
         self.output_symtab_ctx.strsize += @as(u32, @intCast(local.name(elf_file).len)) + 1;
     }
@@ -578,10 +578,10 @@ pub fn updateSymtabSize(self: *ZigObject, elf_file: *Elf) !void {
         if (global.atom(elf_file)) |atom| if (!atom.flags.alive) continue;
         global.flags.output_symtab = true;
         if (global.isLocal(elf_file)) {
-            try global.setOutputSymtabIndex(self.output_symtab_ctx.nlocals, elf_file);
+            try global.addExtra(.{ .symtab = self.output_symtab_ctx.nlocals }, elf_file);
             self.output_symtab_ctx.nlocals += 1;
         } else {
-            try global.setOutputSymtabIndex(self.output_symtab_ctx.nglobals, elf_file);
+            try global.addExtra(.{ .symtab = self.output_symtab_ctx.nglobals }, elf_file);
             self.output_symtab_ctx.nglobals += 1;
         }
         self.output_symtab_ctx.strsize += @as(u32, @intCast(global.name(elf_file).len)) + 1;
@@ -631,7 +631,7 @@ pub fn codeAlloc(self: ZigObject, elf_file: *Elf, atom_index: Atom.Index) ![]u8
         return code;
     }
 
-    const file_offset = shdr.sh_offset + atom.value;
+    const file_offset = shdr.sh_offset + @as(u64, @intCast(atom.value));
     const size = std.math.cast(usize, atom.size) orelse return error.Overflow;
     const code = try gpa.alloc(u8, size);
     errdefer gpa.free(code);
@@ -659,7 +659,7 @@ pub fn getDeclVAddr(
         .r_info = (@as(u64, @intCast(this_sym.esym_index)) << 32) | r_type,
         .r_addend = reloc_info.addend,
     });
-    return vaddr;
+    return @intCast(vaddr);
 }
 
 pub fn getAnonDeclVAddr(
@@ -678,7 +678,7 @@ pub fn getAnonDeclVAddr(
         .r_info = (@as(u64, @intCast(sym.esym_index)) << 32) | r_type,
         .r_addend = reloc_info.addend,
     });
-    return vaddr;
+    return @intCast(vaddr);
 }
 
 pub fn lowerAnonDecl(
@@ -929,7 +929,7 @@ fn updateDeclCode(
 
     if (old_size > 0 and elf_file.base.child_pid == null) {
         const capacity = atom_ptr.capacity(elf_file);
-        const need_realloc = code.len > capacity or !required_alignment.check(atom_ptr.value);
+        const need_realloc = code.len > capacity or !required_alignment.check(@intCast(atom_ptr.value));
         if (need_realloc) {
             try atom_ptr.grow(elf_file);
             log.debug("growing {} from 0x{x} to 0x{x}", .{ decl_name.fmt(&mod.intern_pool), old_vaddr, atom_ptr.value });
@@ -984,7 +984,7 @@ fn updateDeclCode(
 
     const shdr = elf_file.shdrs.items[shdr_index];
     if (shdr.sh_type != elf.SHT_NOBITS) {
-        const file_offset = shdr.sh_offset + atom_ptr.value;
+        const file_offset = shdr.sh_offset + @as(u64, @intCast(atom_ptr.value));
         try elf_file.base.file.?.pwriteAll(code, file_offset);
     }
 }
@@ -1107,7 +1107,7 @@ pub fn updateFunc(
         try self.dwarf.?.commitDeclState(
             mod,
             decl_index,
-            sym.address(.{}, elf_file),
+            @intCast(sym.address(.{}, elf_file)),
             sym.atom(elf_file).?.size,
             ds,
         );
@@ -1186,7 +1186,7 @@ pub fn updateDecl(
         try self.dwarf.?.commitDeclState(
             mod,
             decl_index,
-            sym.address(.{}, elf_file),
+            @intCast(sym.address(.{}, elf_file)),
             sym.atom(elf_file).?.size,
             ds,
         );
@@ -1275,7 +1275,7 @@ fn updateLazySymbol(
     }
 
     const shdr = elf_file.shdrs.items[output_section_index];
-    const file_offset = shdr.sh_offset + atom_ptr.value;
+    const file_offset = shdr.sh_offset + @as(u64, @intCast(atom_ptr.value));
     try elf_file.base.file.?.pwriteAll(code, file_offset);
 }
 
@@ -1373,7 +1373,7 @@ fn lowerConst(
     local_esym.st_value = 0;
 
     const shdr = elf_file.shdrs.items[output_section_index];
-    const file_offset = shdr.sh_offset + atom_ptr.value;
+    const file_offset = shdr.sh_offset + @as(u64, @intCast(atom_ptr.value));
     try elf_file.base.file.?.pwriteAll(code, file_offset);
 
     return .{ .ok = sym_index };
@@ -1457,7 +1457,7 @@ pub fn updateExports(
 
         const actual_esym_index = global_esym_index & symbol_mask;
         const global_esym = &self.global_esyms.items(.elf_sym)[actual_esym_index];
-        global_esym.st_value = elf_file.symbol(sym_index).value;
+        global_esym.st_value = @intCast(elf_file.symbol(sym_index).value);
         global_esym.st_shndx = esym.st_shndx;
         global_esym.st_info = (stb_bits << 4) | stt_bits;
         global_esym.st_name = name_off;
diff --git a/src/link/Elf/gc.zig b/src/link/Elf/gc.zig
index d95dd78b33..49b5664dec 100644
--- a/src/link/Elf/gc.zig
+++ b/src/link/Elf/gc.zig
@@ -68,6 +68,10 @@ fn collectRoots(roots: *std.ArrayList(*Atom), files: []const File.Index, elf_fil
 }
 
 fn markSymbol(sym: *Symbol, roots: *std.ArrayList(*Atom), elf_file: *Elf) !void {
+    if (sym.mergeSubsection(elf_file)) |msub| {
+        msub.alive = true;
+        return;
+    }
     const atom = sym.atom(elf_file) orelse return;
     if (markAtom(atom)) try roots.append(atom);
 }
@@ -96,6 +100,10 @@ fn markLive(atom: *Atom, elf_file: *Elf) void {
 
     for (atom.relocs(elf_file)) |rel| {
         const target_sym = elf_file.symbol(file.symbol(rel.r_sym()));
+        if (target_sym.mergeSubsection(elf_file)) |msub| {
+            msub.alive = true;
+            continue;
+        }
         const target_atom = target_sym.atom(elf_file) orelse continue;
         target_atom.flags.alive = true;
         gc_track_live_log.debug("{}marking live atom({d})", .{ track_live_level, target_atom.atom_index });
diff --git a/src/link/Elf/merge_section.zig b/src/link/Elf/merge_section.zig
new file mode 100644
index 0000000000..ab716794fc
--- /dev/null
+++ b/src/link/Elf/merge_section.zig
@@ -0,0 +1,285 @@
+pub const MergeSection = struct {
+    name_offset: u32 = 0,
+    type: u32 = 0,
+    flags: u64 = 0,
+    output_section_index: u32 = 0,
+    bytes: std.ArrayListUnmanaged(u8) = .{},
+    table: std.HashMapUnmanaged(
+        String,
+        MergeSubsection.Index,
+        IndexContext,
+        std.hash_map.default_max_load_percentage,
+    ) = .{},
+    subsections: std.ArrayListUnmanaged(MergeSubsection.Index) = .{},
+
+    pub fn deinit(msec: *MergeSection, allocator: Allocator) void {
+        msec.bytes.deinit(allocator);
+        msec.table.deinit(allocator);
+        msec.subsections.deinit(allocator);
+    }
+
+    pub fn name(msec: MergeSection, elf_file: *Elf) [:0]const u8 {
+        return elf_file.strings.getAssumeExists(msec.name_offset);
+    }
+
+    pub fn address(msec: MergeSection, elf_file: *Elf) i64 {
+        const shdr = elf_file.shdrs.items[msec.output_section_index];
+        return @intCast(shdr.sh_addr);
+    }
+
+    const InsertResult = struct {
+        found_existing: bool,
+        key: String,
+        sub: *MergeSubsection.Index,
+    };
+
+    pub fn insert(msec: *MergeSection, allocator: Allocator, string: []const u8) !InsertResult {
+        const gop = try msec.table.getOrPutContextAdapted(
+            allocator,
+            string,
+            IndexAdapter{ .bytes = msec.bytes.items },
+            IndexContext{ .bytes = msec.bytes.items },
+        );
+        if (!gop.found_existing) {
+            const index: u32 = @intCast(msec.bytes.items.len);
+            try msec.bytes.appendSlice(allocator, string);
+            gop.key_ptr.* = .{ .pos = index, .len = @intCast(string.len) };
+        }
+        return .{ .found_existing = gop.found_existing, .key = gop.key_ptr.*, .sub = gop.value_ptr };
+    }
+
+    pub fn insertZ(msec: *MergeSection, allocator: Allocator, string: []const u8) !InsertResult {
+        const with_null = try allocator.alloc(u8, string.len + 1);
+        defer allocator.free(with_null);
+        @memcpy(with_null[0..string.len], string);
+        with_null[string.len] = 0;
+        return msec.insert(allocator, with_null);
+    }
+
+    /// Finalizes the merge section and clears hash table.
+    /// Sorts all owned subsections.
+    pub fn finalize(msec: *MergeSection, elf_file: *Elf) !void {
+        const gpa = elf_file.base.comp.gpa;
+        try msec.subsections.ensureTotalCapacityPrecise(gpa, msec.table.count());
+
+        var it = msec.table.iterator();
+        while (it.next()) |entry| {
+            const msub = elf_file.mergeSubsection(entry.value_ptr.*);
+            if (!msub.alive) continue;
+            msec.subsections.appendAssumeCapacity(entry.value_ptr.*);
+        }
+        msec.table.clearAndFree(gpa);
+
+        const sortFn = struct {
+            pub fn sortFn(ctx: *Elf, lhs: MergeSubsection.Index, rhs: MergeSubsection.Index) bool {
+                const lhs_msub = ctx.mergeSubsection(lhs);
+                const rhs_msub = ctx.mergeSubsection(rhs);
+                if (lhs_msub.alignment.compareStrict(.eq, rhs_msub.alignment)) {
+                    if (lhs_msub.size == rhs_msub.size) {
+                        return mem.order(u8, lhs_msub.getString(ctx), rhs_msub.getString(ctx)) == .lt;
+                    }
+                    return lhs_msub.size < rhs_msub.size;
+                }
+                return lhs_msub.alignment.compareStrict(.lt, rhs_msub.alignment);
+            }
+        }.sortFn;
+
+        std.mem.sort(MergeSubsection.Index, msec.subsections.items, elf_file, sortFn);
+    }
+
+    pub const IndexContext = struct {
+        bytes: []const u8,
+
+        pub fn eql(_: @This(), a: String, b: String) bool {
+            return a.pos == b.pos;
+        }
+
+        pub fn hash(ctx: @This(), key: String) u64 {
+            const str = ctx.bytes[key.pos..][0..key.len];
+            return std.hash_map.hashString(str);
+        }
+    };
+
+    pub const IndexAdapter = struct {
+        bytes: []const u8,
+
+        pub fn eql(ctx: @This(), a: []const u8, b: String) bool {
+            const str = ctx.bytes[b.pos..][0..b.len];
+            return mem.eql(u8, a, str);
+        }
+
+        pub fn hash(_: @This(), adapted_key: []const u8) u64 {
+            return std.hash_map.hashString(adapted_key);
+        }
+    };
+
+    pub fn format(
+        msec: MergeSection,
+        comptime unused_fmt_string: []const u8,
+        options: std.fmt.FormatOptions,
+        writer: anytype,
+    ) !void {
+        _ = msec;
+        _ = unused_fmt_string;
+        _ = options;
+        _ = writer;
+        @compileError("do not format MergeSection directly");
+    }
+
+    pub fn fmt(msec: MergeSection, elf_file: *Elf) std.fmt.Formatter(format2) {
+        return .{ .data = .{
+            .msec = msec,
+            .elf_file = elf_file,
+        } };
+    }
+
+    const FormatContext = struct {
+        msec: MergeSection,
+        elf_file: *Elf,
+    };
+
+    pub fn format2(
+        ctx: FormatContext,
+        comptime unused_fmt_string: []const u8,
+        options: std.fmt.FormatOptions,
+        writer: anytype,
+    ) !void {
+        _ = options;
+        _ = unused_fmt_string;
+        const msec = ctx.msec;
+        const elf_file = ctx.elf_file;
+        try writer.print("{s} : @{x} : type({x}) : flags({x})\n", .{
+            msec.name(elf_file),
+            msec.address(elf_file),
+            msec.type,
+            msec.flags,
+        });
+        for (msec.subsections.items) |index| {
+            try writer.print("   {}\n", .{elf_file.mergeSubsection(index).fmt(elf_file)});
+        }
+    }
+
+    pub const Index = u32;
+};
+
+pub const MergeSubsection = struct {
+    value: i64 = 0,
+    merge_section_index: MergeSection.Index = 0,
+    string_index: u32 = 0,
+    size: u32 = 0,
+    alignment: Atom.Alignment = .@"1",
+    entsize: u32 = 0,
+    alive: bool = false,
+
+    pub fn address(msub: MergeSubsection, elf_file: *Elf) i64 {
+        return msub.mergeSection(elf_file).address(elf_file) + msub.value;
+    }
+
+    pub fn mergeSection(msub: MergeSubsection, elf_file: *Elf) *MergeSection {
+        return elf_file.mergeSection(msub.merge_section_index);
+    }
+
+    pub fn getString(msub: MergeSubsection, elf_file: *Elf) []const u8 {
+        const msec = msub.mergeSection(elf_file);
+        return msec.bytes.items[msub.string_index..][0..msub.size];
+    }
+
+    pub fn format(
+        msub: MergeSubsection,
+        comptime unused_fmt_string: []const u8,
+        options: std.fmt.FormatOptions,
+        writer: anytype,
+    ) !void {
+        _ = msub;
+        _ = unused_fmt_string;
+        _ = options;
+        _ = writer;
+        @compileError("do not format MergeSubsection directly");
+    }
+
+    pub fn fmt(msub: MergeSubsection, elf_file: *Elf) std.fmt.Formatter(format2) {
+        return .{ .data = .{
+            .msub = msub,
+            .elf_file = elf_file,
+        } };
+    }
+
+    const FormatContext = struct {
+        msub: MergeSubsection,
+        elf_file: *Elf,
+    };
+
+    pub fn format2(
+        ctx: FormatContext,
+        comptime unused_fmt_string: []const u8,
+        options: std.fmt.FormatOptions,
+        writer: anytype,
+    ) !void {
+        _ = options;
+        _ = unused_fmt_string;
+        const msub = ctx.msub;
+        const elf_file = ctx.elf_file;
+        try writer.print("@{x} : align({x}) : size({x})", .{
+            msub.address(elf_file),
+            msub.alignment,
+            msub.size,
+        });
+        if (!msub.alive) try writer.writeAll(" : [*]");
+    }
+
+    pub const Index = u32;
+};
+
+pub const InputMergeSection = struct {
+    merge_section_index: MergeSection.Index = 0,
+    atom_index: Atom.Index = 0,
+    offsets: std.ArrayListUnmanaged(u32) = .{},
+    subsections: std.ArrayListUnmanaged(MergeSubsection.Index) = .{},
+    bytes: std.ArrayListUnmanaged(u8) = .{},
+    strings: std.ArrayListUnmanaged(String) = .{},
+
+    pub fn deinit(imsec: *InputMergeSection, allocator: Allocator) void {
+        imsec.offsets.deinit(allocator);
+        imsec.subsections.deinit(allocator);
+        imsec.bytes.deinit(allocator);
+        imsec.strings.deinit(allocator);
+    }
+
+    pub fn clearAndFree(imsec: *InputMergeSection, allocator: Allocator) void {
+        imsec.bytes.clearAndFree(allocator);
+        // TODO: imsec.strings.clearAndFree(allocator);
+    }
+
+    pub fn findSubsection(imsec: InputMergeSection, offset: u32) ?struct { MergeSubsection.Index, u32 } {
+        // TODO: binary search
+        for (imsec.offsets.items, 0..) |off, index| {
+            if (offset < off) return .{
+                imsec.subsections.items[index - 1],
+                offset - imsec.offsets.items[index - 1],
+            };
+        }
+        const last = imsec.offsets.items.len - 1;
+        const last_off = imsec.offsets.items[last];
+        const last_len = imsec.strings.items[last].len;
+        if (offset < last_off + last_len) return .{ imsec.subsections.items[last], offset - last_off };
+        return null;
+    }
+
+    pub fn insert(imsec: *InputMergeSection, allocator: Allocator, string: []const u8) !void {
+        const index: u32 = @intCast(imsec.bytes.items.len);
+        try imsec.bytes.appendSlice(allocator, string);
+        try imsec.strings.append(allocator, .{ .pos = index, .len = @intCast(string.len) });
+    }
+
+    pub const Index = u32;
+};
+
+const String = struct { pos: u32, len: u32 };
+
+const assert = std.debug.assert;
+const mem = std.mem;
+const std = @import("std");
+
+const Allocator = mem.Allocator;
+const Atom = @import("Atom.zig");
+const Elf = @import("../Elf.zig");
diff --git a/src/link/Elf/relocatable.zig b/src/link/Elf/relocatable.zig
index 98abed420e..c70faba020 100644
--- a/src/link/Elf/relocatable.zig
+++ b/src/link/Elf/relocatable.zig
@@ -34,12 +34,16 @@ pub fn flushStaticLib(elf_file: *Elf, comp: *Compilation, module_obj_path: ?[]co
     // First, we flush relocatable object file generated with our backends.
     if (elf_file.zigObjectPtr()) |zig_object| {
         zig_object.resolveSymbols(elf_file);
+        try elf_file.addCommentString();
+        try elf_file.finalizeMergeSections();
         zig_object.claimUnresolvedObject(elf_file);
 
+        try elf_file.initMergeSections();
         try elf_file.initSymtab();
         try elf_file.initShStrtab();
         try elf_file.sortShdrs();
         try zig_object.addAtomsToRelaSections(elf_file);
+        try elf_file.updateMergeSectionSizes();
         try updateSectionSizes(elf_file);
 
         try allocateAllocSections(elf_file);
@@ -49,6 +53,7 @@ pub fn flushStaticLib(elf_file: *Elf, comp: *Compilation, module_obj_path: ?[]co
             state_log.debug("{}", .{elf_file.dumpState()});
         }
 
+        try elf_file.writeMergeSections();
         try writeSyntheticSections(elf_file);
         try elf_file.writeShdrTable();
         try elf_file.writeElfHeader();
@@ -179,9 +184,13 @@ pub fn flushObject(elf_file: *Elf, comp: *Compilation, module_obj_path: ?[]const
     // input Object files.
     elf_file.resolveSymbols();
     elf_file.markEhFrameAtomsDead();
+    try elf_file.resolveMergeSections();
+    try elf_file.addCommentString();
+    try elf_file.finalizeMergeSections();
     claimUnresolved(elf_file);
 
     try initSections(elf_file);
+    try elf_file.initMergeSections();
     try elf_file.sortShdrs();
     if (elf_file.zigObjectPtr()) |zig_object| {
         try zig_object.addAtomsToRelaSections(elf_file);
@@ -191,6 +200,7 @@ pub fn flushObject(elf_file: *Elf, comp: *Compilation, module_obj_path: ?[]const
         try object.addAtomsToOutputSections(elf_file);
         try object.addAtomsToRelaSections(elf_file);
     }
+    try elf_file.updateMergeSectionSizes();
     try updateSectionSizes(elf_file);
 
     try allocateAllocSections(elf_file);
@@ -201,6 +211,7 @@ pub fn flushObject(elf_file: *Elf, comp: *Compilation, module_obj_path: ?[]const
     }
 
     try writeAtoms(elf_file);
+    try elf_file.writeMergeSections();
     try writeSyntheticSections(elf_file);
     try elf_file.writeShdrTable();
     try elf_file.writeElfHeader();
@@ -328,7 +339,7 @@ fn updateSectionSizes(elf_file: *Elf) !void {
             if (!atom_ptr.flags.alive) continue;
             const offset = atom_ptr.alignment.forward(shdr.sh_size);
             const padding = offset - shdr.sh_size;
-            atom_ptr.value = offset;
+            atom_ptr.value = @intCast(offset);
             shdr.sh_size += padding + atom_ptr.size;
             shdr.sh_addralign = @max(shdr.sh_addralign, atom_ptr.alignment.toByteUnits() orelse 1);
         }
@@ -434,7 +445,7 @@ fn writeAtoms(elf_file: *Elf) !void {
             const atom_ptr = elf_file.atom(atom_index).?;
             assert(atom_ptr.flags.alive);
 
-            const offset = math.cast(usize, atom_ptr.value - shdr.sh_addr - base_offset) orelse
+            const offset = math.cast(usize, atom_ptr.value - @as(i64, @intCast(shdr.sh_addr - base_offset))) orelse
                 return error.Overflow;
             const size = math.cast(usize, atom_ptr.size) orelse return error.Overflow;
 
diff --git a/src/link/Elf/synthetic_sections.zig b/src/link/Elf/synthetic_sections.zig
index 2ef7d49540..59adc7d40e 100644
--- a/src/link/Elf/synthetic_sections.zig
+++ b/src/link/Elf/synthetic_sections.zig
@@ -259,11 +259,7 @@ pub const ZigGotSection = struct {
         if (elf_file.isEffectivelyDynLib() or (elf_file.base.isExe() and comp.config.pie)) {
             zig_got.flags.needs_rela = true;
         }
-        if (symbol.extra(elf_file)) |extra| {
-            var new_extra = extra;
-            new_extra.zig_got = index;
-            symbol.setExtra(new_extra, elf_file);
-        } else try symbol.addExtra(.{ .zig_got = index }, elf_file);
+        try symbol.addExtra(.{ .zig_got = index }, elf_file);
         return index;
     }
 
@@ -274,11 +270,11 @@ pub const ZigGotSection = struct {
         return shdr.sh_offset + @as(u64, entry_size) * index;
     }
 
-    pub fn entryAddress(zig_got: ZigGotSection, index: Index, elf_file: *Elf) u64 {
+    pub fn entryAddress(zig_got: ZigGotSection, index: Index, elf_file: *Elf) i64 {
         _ = zig_got;
         const entry_size = elf_file.archPtrWidthBytes();
         const shdr = elf_file.shdrs.items[elf_file.zig_got_section_index.?];
-        return shdr.sh_addr + @as(u64, entry_size) * index;
+        return @as(i64, @intCast(shdr.sh_addr)) + entry_size * index;
     }
 
     pub fn size(zig_got: ZigGotSection, elf_file: *Elf) usize {
@@ -295,23 +291,23 @@ pub const ZigGotSection = struct {
         const target = elf_file.getTarget();
         const endian = target.cpu.arch.endian();
         const off = zig_got.entryOffset(index, elf_file);
-        const vaddr = zig_got.entryAddress(index, elf_file);
+        const vaddr: u64 = @intCast(zig_got.entryAddress(index, elf_file));
         const entry = zig_got.entries.items[index];
         const value = elf_file.symbol(entry).address(.{}, elf_file);
         switch (entry_size) {
             2 => {
                 var buf: [2]u8 = undefined;
-                std.mem.writeInt(u16, &buf, @as(u16, @intCast(value)), endian);
+                std.mem.writeInt(u16, &buf, @intCast(value), endian);
                 try elf_file.base.file.?.pwriteAll(&buf, off);
             },
             4 => {
                 var buf: [4]u8 = undefined;
-                std.mem.writeInt(u32, &buf, @as(u32, @intCast(value)), endian);
+                std.mem.writeInt(u32, &buf, @intCast(value), endian);
                 try elf_file.base.file.?.pwriteAll(&buf, off);
             },
             8 => {
                 var buf: [8]u8 = undefined;
-                std.mem.writeInt(u64, &buf, value, endian);
+                std.mem.writeInt(u64, &buf, @intCast(value), endian);
                 try elf_file.base.file.?.pwriteAll(&buf, off);
 
                 if (elf_file.base.child_pid) |pid| {
@@ -360,9 +356,9 @@ pub const ZigGotSection = struct {
             const symbol = elf_file.symbol(entry);
             const offset = symbol.zigGotAddress(elf_file);
             elf_file.addRelaDynAssumeCapacity(.{
-                .offset = offset,
+                .offset = @intCast(offset),
                 .type = relocation.encode(.rel, cpu_arch),
-                .addend = @intCast(symbol.address(.{ .plt = false }, elf_file)),
+                .addend = symbol.address(.{ .plt = false }, elf_file),
             });
         }
     }
@@ -390,7 +386,7 @@ pub const ZigGotSection = struct {
                 .st_info = elf.STT_OBJECT,
                 .st_other = 0,
                 .st_shndx = @intCast(elf_file.zig_got_section_index.?),
-                .st_value = st_value,
+                .st_value = @intCast(st_value),
                 .st_size = st_size,
             };
         }
@@ -461,10 +457,10 @@ pub const GotSection = struct {
             };
         }
 
-        pub fn address(entry: Entry, elf_file: *Elf) u64 {
-            const ptr_bytes = @as(u64, elf_file.archPtrWidthBytes());
+        pub fn address(entry: Entry, elf_file: *Elf) i64 {
+            const ptr_bytes = elf_file.archPtrWidthBytes();
             const shdr = &elf_file.shdrs.items[elf_file.got_section_index.?];
-            return shdr.sh_addr + @as(u64, entry.cell_index) * ptr_bytes;
+            return @as(i64, @intCast(shdr.sh_addr)) + entry.cell_index * ptr_bytes;
         }
     };
 
@@ -499,11 +495,7 @@ pub const GotSection = struct {
         {
             got.flags.needs_rela = true;
         }
-        if (symbol.extra(elf_file)) |extra| {
-            var new_extra = extra;
-            new_extra.got = index;
-            symbol.setExtra(new_extra, elf_file);
-        } else try symbol.addExtra(.{ .got = index }, elf_file);
+        try symbol.addExtra(.{ .got = index }, elf_file);
         return index;
     }
 
@@ -529,11 +521,7 @@ pub const GotSection = struct {
         const symbol = elf_file.symbol(sym_index);
         symbol.flags.has_tlsgd = true;
         if (symbol.flags.import or elf_file.isEffectivelyDynLib()) got.flags.needs_rela = true;
-        if (symbol.extra(elf_file)) |extra| {
-            var new_extra = extra;
-            new_extra.tlsgd = index;
-            symbol.setExtra(new_extra, elf_file);
-        } else try symbol.addExtra(.{ .tlsgd = index }, elf_file);
+        try symbol.addExtra(.{ .tlsgd = index }, elf_file);
     }
 
     pub fn addGotTpSymbol(got: *GotSection, sym_index: Symbol.Index, elf_file: *Elf) !void {
@@ -546,11 +534,7 @@ pub const GotSection = struct {
         const symbol = elf_file.symbol(sym_index);
         symbol.flags.has_gottp = true;
         if (symbol.flags.import or elf_file.isEffectivelyDynLib()) got.flags.needs_rela = true;
-        if (symbol.extra(elf_file)) |extra| {
-            var new_extra = extra;
-            new_extra.gottp = index;
-            symbol.setExtra(new_extra, elf_file);
-        } else try symbol.addExtra(.{ .gottp = index }, elf_file);
+        try symbol.addExtra(.{ .gottp = index }, elf_file);
     }
 
     pub fn addTlsDescSymbol(got: *GotSection, sym_index: Symbol.Index, elf_file: *Elf) !void {
@@ -563,11 +547,7 @@ pub const GotSection = struct {
         const symbol = elf_file.symbol(sym_index);
         symbol.flags.has_tlsdesc = true;
         got.flags.needs_rela = true;
-        if (symbol.extra(elf_file)) |extra| {
-            var new_extra = extra;
-            new_extra.tlsdesc = index;
-            symbol.setExtra(new_extra, elf_file);
-        } else try symbol.addExtra(.{ .tlsdesc = index }, elf_file);
+        try symbol.addExtra(.{ .tlsdesc = index }, elf_file);
     }
 
     pub fn size(got: GotSection, elf_file: *Elf) usize {
@@ -628,8 +608,7 @@ pub const GotSection = struct {
                             0;
                         try writeInt(offset, elf_file, writer);
                     } else {
-                        const offset = @as(i64, @intCast(symbol.?.address(.{}, elf_file))) -
-                            @as(i64, @intCast(elf_file.tpAddress()));
+                        const offset = symbol.?.address(.{}, elf_file) - elf_file.tpAddress();
                         try writeInt(offset, elf_file, writer);
                     }
                 },
@@ -640,7 +619,7 @@ pub const GotSection = struct {
                     } else {
                         try writeInt(0, elf_file, writer);
                         const offset = if (apply_relocs)
-                            @as(i64, @intCast(symbol.?.address(.{}, elf_file))) - @as(i64, @intCast(elf_file.tlsAddress()))
+                            symbol.?.address(.{}, elf_file) - elf_file.tlsAddress()
                         else
                             0;
                         try writeInt(offset, elf_file, writer);
@@ -666,7 +645,7 @@ pub const GotSection = struct {
 
             switch (entry.tag) {
                 .got => {
-                    const offset = symbol.?.gotAddress(elf_file);
+                    const offset: u64 = @intCast(symbol.?.gotAddress(elf_file));
                     if (symbol.?.flags.import) {
                         elf_file.addRelaDynAssumeCapacity(.{
                             .offset = offset,
@@ -679,7 +658,7 @@ pub const GotSection = struct {
                         elf_file.addRelaDynAssumeCapacity(.{
                             .offset = offset,
                             .type = relocation.encode(.irel, cpu_arch),
-                            .addend = @intCast(symbol.?.address(.{ .plt = false }, elf_file)),
+                            .addend = symbol.?.address(.{ .plt = false }, elf_file),
                         });
                         continue;
                     }
@@ -689,14 +668,14 @@ pub const GotSection = struct {
                         elf_file.addRelaDynAssumeCapacity(.{
                             .offset = offset,
                             .type = relocation.encode(.rel, cpu_arch),
-                            .addend = @intCast(symbol.?.address(.{ .plt = false }, elf_file)),
+                            .addend = symbol.?.address(.{ .plt = false }, elf_file),
                         });
                     }
                 },
 
                 .tlsld => {
                     if (is_dyn_lib) {
-                        const offset = entry.address(elf_file);
+                        const offset: u64 = @intCast(entry.address(elf_file));
                         elf_file.addRelaDynAssumeCapacity(.{
                             .offset = offset,
                             .type = relocation.encode(.dtpmod, cpu_arch),
@@ -705,7 +684,7 @@ pub const GotSection = struct {
                 },
 
                 .tlsgd => {
-                    const offset = symbol.?.tlsGdAddress(elf_file);
+                    const offset: u64 = @intCast(symbol.?.tlsGdAddress(elf_file));
                     if (symbol.?.flags.import) {
                         elf_file.addRelaDynAssumeCapacity(.{
                             .offset = offset,
@@ -727,7 +706,7 @@ pub const GotSection = struct {
                 },
 
                 .gottp => {
-                    const offset = symbol.?.gotTpAddress(elf_file);
+                    const offset: u64 = @intCast(symbol.?.gotTpAddress(elf_file));
                     if (symbol.?.flags.import) {
                         elf_file.addRelaDynAssumeCapacity(.{
                             .offset = offset,
@@ -738,18 +717,18 @@ pub const GotSection = struct {
                         elf_file.addRelaDynAssumeCapacity(.{
                             .offset = offset,
                             .type = relocation.encode(.tpoff, cpu_arch),
-                            .addend = @intCast(symbol.?.address(.{}, elf_file) - elf_file.tlsAddress()),
+                            .addend = symbol.?.address(.{}, elf_file) - elf_file.tlsAddress(),
                         });
                     }
                 },
 
                 .tlsdesc => {
-                    const offset = symbol.?.tlsDescAddress(elf_file);
+                    const offset: u64 = @intCast(symbol.?.tlsDescAddress(elf_file));
                     elf_file.addRelaDynAssumeCapacity(.{
                         .offset = offset,
                         .sym = if (symbol.?.flags.import) extra.?.dynamic else 0,
                         .type = relocation.encode(.tlsdesc, cpu_arch),
-                        .addend = if (symbol.?.flags.import) 0 else @intCast(symbol.?.address(.{}, elf_file) - elf_file.tlsAddress()),
+                        .addend = if (symbol.?.flags.import) 0 else symbol.?.address(.{}, elf_file) - elf_file.tlsAddress(),
                     });
                 },
             }
@@ -826,7 +805,7 @@ pub const GotSection = struct {
                 .st_info = elf.STT_OBJECT,
                 .st_other = 0,
                 .st_shndx = @intCast(elf_file.got_section_index.?),
-                .st_value = st_value,
+                .st_value = @intCast(st_value),
                 .st_size = st_size,
             };
         }
@@ -877,11 +856,7 @@ pub const PltSection = struct {
         const index = @as(u32, @intCast(plt.symbols.items.len));
         const symbol = elf_file.symbol(sym_index);
         symbol.flags.has_plt = true;
-        if (symbol.extra(elf_file)) |extra| {
-            var new_extra = extra;
-            new_extra.plt = index;
-            symbol.setExtra(new_extra, elf_file);
-        } else try symbol.addExtra(.{ .plt = index }, elf_file);
+        try symbol.addExtra(.{ .plt = index }, elf_file);
         try plt.symbols.append(gpa, sym_index);
     }
 
@@ -924,7 +899,7 @@ pub const PltSection = struct {
             const sym = elf_file.symbol(sym_index);
             assert(sym.flags.import);
             const extra = sym.extra(elf_file).?;
-            const r_offset = sym.gotPltAddress(elf_file);
+            const r_offset: u64 = @intCast(sym.gotPltAddress(elf_file));
             const r_sym: u64 = extra.dynamic;
             const r_type = relocation.encode(.jump_slot, cpu_arch);
             elf_file.rela_plt.appendAssumeCapacity(.{
@@ -960,7 +935,7 @@ pub const PltSection = struct {
                 .st_info = elf.STT_FUNC,
                 .st_other = 0,
                 .st_shndx = @intCast(elf_file.plt_section_index.?),
-                .st_value = sym.pltAddress(elf_file),
+                .st_value = @intCast(sym.pltAddress(elf_file)),
                 .st_size = entrySize(cpu_arch),
             };
         }
@@ -1033,13 +1008,13 @@ pub const PltSection = struct {
     const aarch64 = struct {
         fn write(plt: PltSection, elf_file: *Elf, writer: anytype) !void {
             {
-                const plt_addr = elf_file.shdrs.items[elf_file.plt_section_index.?].sh_addr;
-                const got_plt_addr = elf_file.shdrs.items[elf_file.got_plt_section_index.?].sh_addr;
+                const plt_addr: i64 = @intCast(elf_file.shdrs.items[elf_file.plt_section_index.?].sh_addr);
+                const got_plt_addr: i64 = @intCast(elf_file.shdrs.items[elf_file.got_plt_section_index.?].sh_addr);
                 // TODO: relax if possible
                 // .got.plt[2]
                 const pages = try aarch64_util.calcNumberOfPages(plt_addr + 4, got_plt_addr + 16);
-                const ldr_off = try math.divExact(u12, @truncate(got_plt_addr + 16), 8);
-                const add_off: u12 = @truncate(got_plt_addr + 16);
+                const ldr_off = try math.divExact(u12, @truncate(@as(u64, @bitCast(got_plt_addr + 16))), 8);
+                const add_off: u12 = @truncate(@as(u64, @bitCast(got_plt_addr + 16)));
 
                 const preamble = &[_]Instruction{
                     Instruction.stp(
@@ -1067,8 +1042,8 @@ pub const PltSection = struct {
                 const target_addr = sym.gotPltAddress(elf_file);
                 const source_addr = sym.pltAddress(elf_file);
                 const pages = try aarch64_util.calcNumberOfPages(source_addr, target_addr);
-                const ldr_off = try math.divExact(u12, @truncate(target_addr), 8);
-                const add_off: u12 = @truncate(target_addr);
+                const ldr_off = try math.divExact(u12, @truncate(@as(u64, @bitCast(target_addr))), 8);
+                const add_off: u12 = @truncate(@as(u64, @bitCast(target_addr)));
                 const insts = &[_]Instruction{
                     Instruction.adrp(.x16, pages),
                     Instruction.ldr(.x17, .x16, Instruction.LoadStoreOffset.imm(ldr_off)),
@@ -1101,7 +1076,7 @@ pub const GotPltSection = struct {
         {
             // [0]: _DYNAMIC
             const symbol = elf_file.symbol(elf_file.dynamic_index.?);
-            try writer.writeInt(u64, symbol.address(.{}, elf_file), .little);
+            try writer.writeInt(u64, @intCast(symbol.address(.{}, elf_file)), .little);
         }
         // [1]: 0x0
         // [2]: 0x0
@@ -1132,11 +1107,7 @@ pub const PltGotSection = struct {
         const symbol = elf_file.symbol(sym_index);
         symbol.flags.has_plt = true;
         symbol.flags.has_got = true;
-        if (symbol.extra(elf_file)) |extra| {
-            var new_extra = extra;
-            new_extra.plt_got = index;
-            symbol.setExtra(new_extra, elf_file);
-        } else try symbol.addExtra(.{ .plt_got = index }, elf_file);
+        try symbol.addExtra(.{ .plt_got = index }, elf_file);
         try plt_got.symbols.append(gpa, sym_index);
     }
 
@@ -1181,7 +1152,7 @@ pub const PltGotSection = struct {
                 .st_info = elf.STT_FUNC,
                 .st_other = 0,
                 .st_shndx = @intCast(elf_file.plt_got_section_index.?),
-                .st_value = sym.pltGotAddress(elf_file),
+                .st_value = @intCast(sym.pltGotAddress(elf_file)),
                 .st_size = 16,
             };
         }
@@ -1212,7 +1183,7 @@ pub const PltGotSection = struct {
                 const target_addr = sym.gotAddress(elf_file);
                 const source_addr = sym.pltGotAddress(elf_file);
                 const pages = try aarch64_util.calcNumberOfPages(source_addr, target_addr);
-                const off = try math.divExact(u12, @truncate(target_addr), 8);
+                const off = try math.divExact(u12, @truncate(@as(u64, @bitCast(target_addr))), 8);
                 const insts = &[_]Instruction{
                     Instruction.adrp(.x16, pages),
                     Instruction.ldr(.x17, .x16, Instruction.LoadStoreOffset.imm(off)),
@@ -1248,12 +1219,7 @@ pub const CopyRelSection = struct {
         symbol.flags.@"export" = true;
         symbol.flags.has_copy_rel = true;
         symbol.flags.weak = false;
-
-        if (symbol.extra(elf_file)) |extra| {
-            var new_extra = extra;
-            new_extra.copy_rel = index;
-            symbol.setExtra(new_extra, elf_file);
-        } else try symbol.addExtra(.{ .copy_rel = index }, elf_file);
+        try symbol.addExtra(.{ .copy_rel = index }, elf_file);
         try copy_rel.symbols.append(gpa, sym_index);
 
         const shared_object = symbol.file(elf_file).?.shared_object;
@@ -1280,9 +1246,9 @@ pub const CopyRelSection = struct {
             const symbol = elf_file.symbol(sym_index);
             const shared_object = symbol.file(elf_file).?.shared_object;
             const alignment = try symbol.dsoAlignment(elf_file);
-            symbol.value = mem.alignForward(u64, shdr.sh_size, alignment);
+            symbol.value = @intCast(mem.alignForward(u64, shdr.sh_size, alignment));
             shdr.sh_addralign = @max(shdr.sh_addralign, alignment);
-            shdr.sh_size = symbol.value + symbol.elfSym(elf_file).st_size;
+            shdr.sh_size = @as(u64, @intCast(symbol.value)) + symbol.elfSym(elf_file).st_size;
 
             const aliases = shared_object.symbolAliases(sym_index, elf_file);
             for (aliases) |alias| {
@@ -1303,7 +1269,7 @@ pub const CopyRelSection = struct {
             assert(sym.flags.import and sym.flags.has_copy_rel);
             const extra = sym.extra(elf_file).?;
             elf_file.addRelaDynAssumeCapacity(.{
-                .offset = sym.address(.{}, elf_file),
+                .offset = @intCast(sym.address(.{}, elf_file)),
                 .sym = extra.dynamic,
                 .type = relocation.encode(.copy, cpu_arch),
             });
@@ -1335,11 +1301,7 @@ pub const DynsymSection = struct {
         const index = @as(u32, @intCast(dynsym.entries.items.len + 1));
         const sym = elf_file.symbol(sym_index);
         sym.flags.has_dynamic = true;
-        if (sym.extra(elf_file)) |extra| {
-            var new_extra = extra;
-            new_extra.dynamic = index;
-            sym.setExtra(new_extra, elf_file);
-        } else try sym.addExtra(.{ .dynamic = index }, elf_file);
+        try sym.addExtra(.{ .dynamic = index }, elf_file);
         const off = try elf_file.insertDynString(sym.name(elf_file));
         try dynsym.entries.append(gpa, .{ .symbol_index = sym_index, .off = off });
     }
diff --git a/src/link/Elf/thunks.zig b/src/link/Elf/thunks.zig
index 7d06b3b190..48694416c9 100644
--- a/src/link/Elf/thunks.zig
+++ b/src/link/Elf/thunks.zig
@@ -7,7 +7,7 @@ pub fn createThunks(shndx: u32, elf_file: *Elf) !void {
     assert(atoms.len > 0);
 
     for (atoms) |atom_index| {
-        elf_file.atom(atom_index).?.value = @bitCast(@as(i64, -1));
+        elf_file.atom(atom_index).?.value = -1;
     }
 
     var i: usize = 0;
@@ -22,7 +22,8 @@ pub fn createThunks(shndx: u32, elf_file: *Elf) !void {
             const atom_index = atoms[i];
             const atom = elf_file.atom(atom_index).?;
             assert(atom.flags.alive);
-            if (atom.alignment.forward(shdr.sh_size) - start_atom.value >= max_distance) break;
+            if (@as(i64, @intCast(atom.alignment.forward(shdr.sh_size))) - start_atom.value >= max_distance)
+                break;
             atom.value = try advance(shdr, atom.size, atom.alignment);
         }
 
@@ -50,7 +51,8 @@ pub fn createThunks(shndx: u32, elf_file: *Elf) !void {
                 };
                 try thunk.symbols.put(gpa, target, {});
             }
-            atom.thunk_index = thunk_index;
+            try atom.addExtra(.{ .thunk = thunk_index }, elf_file);
+            atom.flags.thunk = true;
         }
 
         thunk.value = try advance(shdr, thunk.size(elf_file), Atom.Alignment.fromNonzeroByteUnits(2));
@@ -59,12 +61,12 @@ pub fn createThunks(shndx: u32, elf_file: *Elf) !void {
     }
 }
 
-fn advance(shdr: *elf.Elf64_Shdr, size: u64, alignment: Atom.Alignment) !u64 {
+fn advance(shdr: *elf.Elf64_Shdr, size: u64, alignment: Atom.Alignment) !i64 {
     const offset = alignment.forward(shdr.sh_size);
     const padding = offset - shdr.sh_size;
     shdr.sh_size += padding + size;
     shdr.sh_addralign = @max(shdr.sh_addralign, alignment.toByteUnits() orelse 1);
-    return offset;
+    return @intCast(offset);
 }
 
 /// A branch will need an extender if its target is larger than
@@ -78,7 +80,7 @@ fn maxAllowedDistance(cpu_arch: std.Target.Cpu.Arch) u32 {
 }
 
 pub const Thunk = struct {
-    value: u64 = 0,
+    value: i64 = 0,
     output_section_index: u32 = 0,
     symbols: std.AutoArrayHashMapUnmanaged(Symbol.Index, void) = .{},
     output_symtab_ctx: Elf.SymtabCtx = .{},
@@ -92,14 +94,14 @@ pub const Thunk = struct {
         return thunk.symbols.keys().len * trampolineSize(cpu_arch);
     }
 
-    pub fn address(thunk: Thunk, elf_file: *Elf) u64 {
+    pub fn address(thunk: Thunk, elf_file: *Elf) i64 {
         const shdr = elf_file.shdrs.items[thunk.output_section_index];
-        return shdr.sh_addr + thunk.value;
+        return @as(i64, @intCast(shdr.sh_addr)) + thunk.value;
     }
 
-    pub fn targetAddress(thunk: Thunk, sym_index: Symbol.Index, elf_file: *Elf) u64 {
+    pub fn targetAddress(thunk: Thunk, sym_index: Symbol.Index, elf_file: *Elf) i64 {
         const cpu_arch = elf_file.getTarget().cpu.arch;
-        return thunk.address(elf_file) + thunk.symbols.getIndex(sym_index).? * trampolineSize(cpu_arch);
+        return thunk.address(elf_file) + @as(i64, @intCast(thunk.symbols.getIndex(sym_index).? * trampolineSize(cpu_arch)));
     }
 
     pub fn write(thunk: Thunk, elf_file: *Elf, writer: anytype) !void {
@@ -131,7 +133,7 @@ pub const Thunk = struct {
                 .st_info = elf.STT_FUNC,
                 .st_other = 0,
                 .st_shndx = @intCast(thunk.output_section_index),
-                .st_value = thunk.targetAddress(sym_index, elf_file),
+                .st_value = @intCast(thunk.targetAddress(sym_index, elf_file)),
                 .st_size = trampolineSize(cpu_arch),
             };
         }
@@ -204,9 +206,9 @@ const aarch64 = struct {
         if (target.flags.has_plt) return false;
         if (atom.output_section_index != target.output_section_index) return false;
         const target_atom = target.atom(elf_file).?;
-        if (target_atom.value == @as(u64, @bitCast(@as(i64, -1)))) return false;
-        const saddr = @as(i64, @intCast(atom.address(elf_file) + rel.r_offset));
-        const taddr: i64 = @intCast(target.address(.{}, elf_file));
+        if (target_atom.value == -1) return false;
+        const saddr = atom.address(elf_file) + @as(i64, @intCast(rel.r_offset));
+        const taddr = target.address(.{}, elf_file);
         _ = math.cast(i28, taddr + rel.r_addend - saddr) orelse return false;
         return true;
     }
@@ -214,11 +216,11 @@ const aarch64 = struct {
     fn write(thunk: Thunk, elf_file: *Elf, writer: anytype) !void {
         for (thunk.symbols.keys(), 0..) |sym_index, i| {
             const sym = elf_file.symbol(sym_index);
-            const saddr = thunk.address(elf_file) + i * trampoline_size;
+            const saddr = thunk.address(elf_file) + @as(i64, @intCast(i * trampoline_size));
             const taddr = sym.address(.{}, elf_file);
             const pages = try util.calcNumberOfPages(saddr, taddr);
             try writer.writeInt(u32, Instruction.adrp(.x16, pages).toU32(), .little);
-            const off: u12 = @truncate(taddr);
+            const off: u12 = @truncate(@as(u64, @bitCast(taddr)));
             try writer.writeInt(u32, Instruction.add(.x16, .x16, off, false).toU32(), .little);
             try writer.writeInt(u32, Instruction.br(.x16).toU32(), .little);
         }
diff --git a/src/link/MachO.zig b/src/link/MachO.zig
index 01e03a10ba..abfae6066f 100644
--- a/src/link/MachO.zig
+++ b/src/link/MachO.zig
@@ -797,6 +797,14 @@ fn dumpArgv(self: *MachO, comp: *Compilation) !void {
             try argv.appendSlice(&.{ "-e", entry_name });
         }
 
+        try argv.append("-o");
+        try argv.append(full_out_path);
+
+        if (self.base.isDynLib() and self.base.allow_shlib_undefined) {
+            try argv.append("-undefined");
+            try argv.append("dynamic_lookup");
+        }
+
         for (comp.objects) |obj| {
             // TODO: verify this
             if (obj.must_link) {
@@ -813,19 +821,11 @@ fn dumpArgv(self: *MachO, comp: *Compilation) !void {
             try argv.append(p);
         }
 
-        if (comp.compiler_rt_lib) |lib| try argv.append(lib.full_object_path);
-        if (comp.compiler_rt_obj) |obj| try argv.append(obj.full_object_path);
-
-        if (comp.config.link_libcpp) {
-            try argv.append(comp.libcxxabi_static_lib.?.full_object_path);
-            try argv.append(comp.libcxx_static_lib.?.full_object_path);
+        for (self.lib_dirs) |lib_dir| {
+            const arg = try std.fmt.allocPrint(arena, "-L{s}", .{lib_dir});
+            try argv.append(arg);
         }
 
-        try argv.append("-o");
-        try argv.append(full_out_path);
-
-        try argv.append("-lSystem");
-
         for (comp.system_libs.keys()) |l_name| {
             const info = comp.system_libs.get(l_name).?;
             const arg = if (info.needed)
@@ -837,9 +837,9 @@ fn dumpArgv(self: *MachO, comp: *Compilation) !void {
             try argv.append(arg);
         }
 
-        for (self.lib_dirs) |lib_dir| {
-            const arg = try std.fmt.allocPrint(arena, "-L{s}", .{lib_dir});
-            try argv.append(arg);
+        for (self.framework_dirs) |f_dir| {
+            try argv.append("-F");
+            try argv.append(f_dir);
         }
 
         for (self.frameworks) |framework| {
@@ -853,15 +853,15 @@ fn dumpArgv(self: *MachO, comp: *Compilation) !void {
             try argv.append(arg);
         }
 
-        for (self.framework_dirs) |f_dir| {
-            try argv.append("-F");
-            try argv.append(f_dir);
+        if (comp.config.link_libcpp) {
+            try argv.append(comp.libcxxabi_static_lib.?.full_object_path);
+            try argv.append(comp.libcxx_static_lib.?.full_object_path);
         }
 
-        if (self.base.isDynLib() and self.base.allow_shlib_undefined) {
-            try argv.append("-undefined");
-            try argv.append("dynamic_lookup");
-        }
+        try argv.append("-lSystem");
+
+        if (comp.compiler_rt_lib) |lib| try argv.append(lib.full_object_path);
+        if (comp.compiler_rt_obj) |obj| try argv.append(obj.full_object_path);
     }
 
     Compilation.dump_argv(argv.items);
diff --git a/src/link/MachO/Archive.zig b/src/link/MachO/Archive.zig
index 9285d5998b..c1ce582036 100644
--- a/src/link/MachO/Archive.zig
+++ b/src/link/MachO/Archive.zig
@@ -70,6 +70,7 @@ pub fn parse(self: *Archive, macho_file: *MachO, path: []const u8, handle_index:
             .archive = .{
                 .path = try gpa.dupe(u8, path),
                 .offset = pos,
+                .size = hdr_size,
             },
             .path = try gpa.dupe(u8, name),
             .file_handle = handle_index,
diff --git a/src/link/MachO/Atom.zig b/src/link/MachO/Atom.zig
index b4600176ce..86edceda05 100644
--- a/src/link/MachO/Atom.zig
+++ b/src/link/MachO/Atom.zig
@@ -770,7 +770,7 @@ fn resolveRelocInner(
                 };
                 break :target math.cast(u64, target) orelse return error.Overflow;
             };
-            const pages = @as(u21, @bitCast(try aarch64.calcNumberOfPages(source, target)));
+            const pages = @as(u21, @bitCast(try aarch64.calcNumberOfPages(@intCast(source), @intCast(target))));
             aarch64.writeAdrpInst(pages, code[rel_offset..][0..4]);
         },
 
diff --git a/src/link/MachO/Object.zig b/src/link/MachO/Object.zig
index 5d2f537a4f..dcdb50ab0e 100644
--- a/src/link/MachO/Object.zig
+++ b/src/link/MachO/Object.zig
@@ -34,6 +34,7 @@ output_ar_state: Archive.ArState = .{},
 const InArchive = struct {
     path: []const u8,
     offset: u64,
+    size: u32,
 };
 
 pub fn isObject(path: []const u8) !bool {
@@ -1330,14 +1331,16 @@ pub fn updateArSymtab(self: Object, ar_symtab: *Archive.ArSymtab, macho_file: *M
 }
 
 pub fn updateArSize(self: *Object, macho_file: *MachO) !void {
-    const file = macho_file.getFileHandle(self.file_handle);
-    const size = (try file.stat()).size;
-    self.output_ar_state.size = size;
+    self.output_ar_state.size = if (self.archive) |ar| ar.size else size: {
+        const file = macho_file.getFileHandle(self.file_handle);
+        break :size (try file.stat()).size;
+    };
 }
 
 pub fn writeAr(self: Object, ar_format: Archive.Format, macho_file: *MachO, writer: anytype) !void {
     // Header
     const size = std.math.cast(usize, self.output_ar_state.size) orelse return error.Overflow;
+    const offset: u64 = if (self.archive) |ar| ar.offset else 0;
     try Archive.writeHeader(self.path, size, ar_format, writer);
     // Data
     const file = macho_file.getFileHandle(self.file_handle);
@@ -1345,7 +1348,7 @@ pub fn writeAr(self: Object, ar_format: Archive.Format, macho_file: *MachO, writ
     const gpa = macho_file.base.comp.gpa;
     const data = try gpa.alloc(u8, size);
     defer gpa.free(data);
-    const amt = try file.preadAll(data, 0);
+    const amt = try file.preadAll(data, offset);
     if (amt != size) return error.InputOutput;
     try writer.writeAll(data);
 }
@@ -1385,7 +1388,6 @@ pub fn calcSymtabSize(self: *Object, macho_file: *MachO) !void {
 
 pub fn calcStabsSize(self: *Object, macho_file: *MachO) error{Overflow}!void {
     if (self.dwarf_info) |dw| {
-        // TODO handle multiple CUs
         const cu = dw.compile_units.items[0];
         const comp_dir = try cu.getCompileDir(dw) orelse return;
         const tu_name = try cu.getSourceFile(dw) orelse return;
@@ -1504,7 +1506,6 @@ pub fn writeStabs(self: *const Object, macho_file: *MachO, ctx: anytype) error{O
     var index = self.output_symtab_ctx.istab;
 
     if (self.dwarf_info) |dw| {
-        // TODO handle multiple CUs
         const cu = dw.compile_units.items[0];
         const comp_dir = try cu.getCompileDir(dw) orelse return;
         const tu_name = try cu.getSourceFile(dw) orelse return;
@@ -1750,7 +1751,6 @@ pub fn hasEhFrameRecords(self: Object) bool {
     return self.cies.items.len > 0;
 }
 
-/// TODO handle multiple CUs
 pub fn hasDebugInfo(self: Object) bool {
     if (self.dwarf_info) |dw| {
         return dw.compile_units.items.len > 0;
diff --git a/src/link/MachO/synthetic.zig b/src/link/MachO/synthetic.zig
index 863b68f9b1..a7729b9137 100644
--- a/src/link/MachO/synthetic.zig
+++ b/src/link/MachO/synthetic.zig
@@ -267,7 +267,7 @@ pub const StubsSection = struct {
                 },
                 .aarch64 => {
                     // TODO relax if possible
-                    const pages = try aarch64.calcNumberOfPages(source, target);
+                    const pages = try aarch64.calcNumberOfPages(@intCast(source), @intCast(target));
                     try writer.writeInt(u32, aarch64.Instruction.adrp(.x16, pages).toU32(), .little);
                     const off = try math.divExact(u12, @truncate(target), 8);
                     try writer.writeInt(
@@ -411,7 +411,7 @@ pub const StubsHelperSection = struct {
             .aarch64 => {
                 {
                     // TODO relax if possible
-                    const pages = try aarch64.calcNumberOfPages(sect.addr, dyld_private_addr);
+                    const pages = try aarch64.calcNumberOfPages(@intCast(sect.addr), @intCast(dyld_private_addr));
                     try writer.writeInt(u32, aarch64.Instruction.adrp(.x17, pages).toU32(), .little);
                     const off: u12 = @truncate(dyld_private_addr);
                     try writer.writeInt(u32, aarch64.Instruction.add(.x17, .x17, off, false).toU32(), .little);
@@ -424,7 +424,7 @@ pub const StubsHelperSection = struct {
                 ).toU32(), .little);
                 {
                     // TODO relax if possible
-                    const pages = try aarch64.calcNumberOfPages(sect.addr + 12, dyld_stub_binder_addr);
+                    const pages = try aarch64.calcNumberOfPages(@intCast(sect.addr + 12), @intCast(dyld_stub_binder_addr));
                     try writer.writeInt(u32, aarch64.Instruction.adrp(.x16, pages).toU32(), .little);
                     const off = try math.divExact(u12, @truncate(dyld_stub_binder_addr), 8);
                     try writer.writeInt(u32, aarch64.Instruction.ldr(
@@ -679,7 +679,7 @@ pub const ObjcStubsSection = struct {
                     {
                         const target = sym.getObjcSelrefsAddress(macho_file);
                         const source = addr;
-                        const pages = try aarch64.calcNumberOfPages(source, target);
+                        const pages = try aarch64.calcNumberOfPages(@intCast(source), @intCast(target));
                         try writer.writeInt(u32, aarch64.Instruction.adrp(.x1, pages).toU32(), .little);
                         const off = try math.divExact(u12, @truncate(target), 8);
                         try writer.writeInt(
@@ -692,7 +692,7 @@ pub const ObjcStubsSection = struct {
                         const target_sym = macho_file.getSymbol(macho_file.objc_msg_send_index.?);
                         const target = target_sym.getGotAddress(macho_file);
                         const source = addr + 2 * @sizeOf(u32);
-                        const pages = try aarch64.calcNumberOfPages(source, target);
+                        const pages = try aarch64.calcNumberOfPages(@intCast(source), @intCast(target));
                         try writer.writeInt(u32, aarch64.Instruction.adrp(.x16, pages).toU32(), .little);
                         const off = try math.divExact(u12, @truncate(target), 8);
                         try writer.writeInt(
diff --git a/src/link/MachO/thunks.zig b/src/link/MachO/thunks.zig
index 02dacc1aec..f66a990b1d 100644
--- a/src/link/MachO/thunks.zig
+++ b/src/link/MachO/thunks.zig
@@ -99,7 +99,7 @@ pub const Thunk = struct {
             const sym = macho_file.getSymbol(sym_index);
             const saddr = thunk.getAddress(macho_file) + i * trampoline_size;
             const taddr = sym.getAddress(.{}, macho_file);
-            const pages = try aarch64.calcNumberOfPages(saddr, taddr);
+            const pages = try aarch64.calcNumberOfPages(@intCast(saddr), @intCast(taddr));
             try writer.writeInt(u32, aarch64.Instruction.adrp(.x16, pages).toU32(), .little);
             const off: u12 = @truncate(taddr);
             try writer.writeInt(u32, aarch64.Instruction.add(.x16, .x16, off, false).toU32(), .little);
diff --git a/src/link/aarch64.zig b/src/link/aarch64.zig
index 576249e988..8b79810c8d 100644
--- a/src/link/aarch64.zig
+++ b/src/link/aarch64.zig
@@ -25,7 +25,7 @@ pub fn writeLoadStoreRegInst(value: u12, code: *[4]u8) void {
     mem.writeInt(u32, code, inst.toU32(), .little);
 }
 
-pub fn calcNumberOfPages(saddr: u64, taddr: u64) error{Overflow}!i21 {
+pub fn calcNumberOfPages(saddr: i64, taddr: i64) error{Overflow}!i21 {
     const spage = math.cast(i32, saddr >> 12) orelse return error.Overflow;
     const tpage = math.cast(i32, taddr >> 12) orelse return error.Overflow;
     const pages = math.cast(i21, tpage - spage) orelse return error.Overflow;
diff --git a/test/behavior.zig b/test/behavior.zig
index 3081f6c9f9..ea8ea713ac 100644
--- a/test/behavior.zig
+++ b/test/behavior.zig
@@ -89,6 +89,7 @@ test {
     _ = @import("behavior/switch.zig");
     _ = @import("behavior/switch_prong_err_enum.zig");
     _ = @import("behavior/switch_prong_implicit_cast.zig");
+    _ = @import("behavior/switch_on_captured_error.zig");
     _ = @import("behavior/this.zig");
     _ = @import("behavior/threadlocal.zig");
     _ = @import("behavior/truncate.zig");
diff --git a/test/behavior/switch_on_captured_error.zig b/test/behavior/switch_on_captured_error.zig
index f5ba762559..6e70c851b1 100644
--- a/test/behavior/switch_on_captured_error.zig
+++ b/test/behavior/switch_on_captured_error.zig
@@ -3,9 +3,11 @@ const assert = std.debug.assert;
 const expect = std.testing.expect;
 const expectError = std.testing.expectError;
 const expectEqual = std.testing.expectEqual;
+const builtin = @import("builtin");
 
 test "switch on error union catch capture" {
     if (builtin.zig_backend == .stage2_spirv64) return error.SkipZigTest;
+    if (builtin.zig_backend == .stage2_wasm) return error.SkipZigTest;
 
     const S = struct {
         const Error = error{ A, B, C };
@@ -16,6 +18,7 @@ test "switch on error union catch capture" {
             try testCapture();
             try testInline();
             try testEmptyErrSet();
+            try testAddressOf();
         }
 
         fn testScalar() !void {
@@ -252,6 +255,44 @@ test "switch on error union catch capture" {
                 try expectEqual(@as(u64, 0), b);
             }
         }
+
+        fn testAddressOf() !void {
+            {
+                const a: anyerror!usize = 0;
+                const ptr = &(a catch |e| switch (e) {
+                    else => 3,
+                });
+                comptime assert(@TypeOf(ptr) == *const usize);
+                try expectEqual(ptr, &(a catch unreachable));
+            }
+            {
+                const a: anyerror!usize = error.A;
+                const ptr = &(a catch |e| switch (e) {
+                    else => 3,
+                });
+                comptime assert(@TypeOf(ptr) == *const comptime_int);
+                try expectEqual(3, ptr.*);
+            }
+            {
+                var a: anyerror!usize = 0;
+                _ = &a;
+                const ptr = &(a catch |e| switch (e) {
+                    else => return,
+                });
+                comptime assert(@TypeOf(ptr) == *usize);
+                ptr.* += 1;
+                try expectEqual(@as(usize, 1), a catch unreachable);
+            }
+            {
+                var a: anyerror!usize = error.A;
+                _ = &a;
+                const ptr = &(a catch |e| switch (e) {
+                    else => return,
+                });
+                comptime assert(@TypeOf(ptr) == *usize);
+                unreachable;
+            }
+        }
     };
 
     try comptime S.doTheTest();
@@ -260,6 +301,7 @@ test "switch on error union catch capture" {
 
 test "switch on error union if else capture" {
     if (builtin.zig_backend == .stage2_spirv64) return error.SkipZigTest;
+    if (builtin.zig_backend == .stage2_wasm) return error.SkipZigTest;
 
     const S = struct {
         const Error = error{ A, B, C };
@@ -276,6 +318,7 @@ test "switch on error union if else capture" {
             try testInlinePtr();
             try testEmptyErrSet();
             try testEmptyErrSetPtr();
+            try testAddressOf();
         }
 
         fn testScalar() !void {
@@ -747,6 +790,45 @@ test "switch on error union if else capture" {
                 try expectEqual(@as(u64, 0), b);
             }
         }
+
+        fn testAddressOf() !void {
+            if (builtin.zig_backend == .stage2_wasm) return error.SkipZigTest;
+            {
+                const a: anyerror!usize = 0;
+                const ptr = &(if (a) |*v| v.* else |e| switch (e) {
+                    else => 3,
+                });
+                comptime assert(@TypeOf(ptr) == *const usize);
+                try expectEqual(ptr, &(a catch unreachable));
+            }
+            {
+                const a: anyerror!usize = error.A;
+                const ptr = &(if (a) |*v| v.* else |e| switch (e) {
+                    else => 3,
+                });
+                comptime assert(@TypeOf(ptr) == *const comptime_int);
+                try expectEqual(3, ptr.*);
+            }
+            {
+                var a: anyerror!usize = 0;
+                _ = &a;
+                const ptr = &(if (a) |*v| v.* else |e| switch (e) {
+                    else => return,
+                });
+                comptime assert(@TypeOf(ptr) == *usize);
+                ptr.* += 1;
+                try expectEqual(@as(usize, 1), a catch unreachable);
+            }
+            {
+                var a: anyerror!usize = error.A;
+                _ = &a;
+                const ptr = &(if (a) |*v| v.* else |e| switch (e) {
+                    else => return,
+                });
+                comptime assert(@TypeOf(ptr) == *usize);
+                unreachable;
+            }
+        }
     };
 
     try comptime S.doTheTest();
diff --git a/test/behavior/union.zig b/test/behavior/union.zig
index 5ed336b50b..b652d52896 100644
--- a/test/behavior/union.zig
+++ b/test/behavior/union.zig
@@ -2301,3 +2301,25 @@ test "matching captures causes union equivalence" {
     comptime assert(@TypeOf(a) == @TypeOf(b));
     try expect(a.u == b.u);
 }
+
+test "signed enum tag with negative value" {
+    if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_x86) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_spirv64) return error.SkipZigTest;
+
+    const Enum = enum(i8) {
+        a = -1,
+    };
+
+    const Union = union(Enum) {
+        a: i32,
+    };
+
+    var i: i32 = 0;
+    i = i;
+    const e = Union{ .a = i };
+
+    try expect(e.a == i);
+}
diff --git a/test/c_abi/cfuncs.c b/test/c_abi/cfuncs.c
index c6477a3d9d..e948c067ac 100644
--- a/test/c_abi/cfuncs.c
+++ b/test/c_abi/cfuncs.c
@@ -269,6 +269,33 @@ void c_struct_f32_f32f32(struct Struct_f32_f32f32 s) {
     assert_or_panic(s.b.d == 3.0f);
 }
 
+struct Struct_u32_Union_u32_u32u32 {
+    uint32_t a;
+    union {
+        struct {
+            uint32_t d, e;
+        } c;
+    } b;
+};
+
+struct Struct_u32_Union_u32_u32u32 zig_ret_struct_u32_union_u32_u32u32(void);
+
+void zig_struct_u32_union_u32_u32u32(struct Struct_u32_Union_u32_u32u32);
+
+struct Struct_u32_Union_u32_u32u32 c_ret_struct_u32_union_u32_u32u32(void) {
+    struct Struct_u32_Union_u32_u32u32 s;
+    s.a = 1;
+    s.b.c.d = 2;
+    s.b.c.e = 3;
+    return s;
+}
+
+void c_struct_u32_union_u32_u32u32(struct Struct_u32_Union_u32_u32u32 s) {
+    assert_or_panic(s.a == 1);
+    assert_or_panic(s.b.c.d == 2);
+    assert_or_panic(s.b.c.e == 3);
+}
+
 struct BigStruct {
     uint64_t a;
     uint64_t b;
@@ -2664,6 +2691,16 @@ void run_c_tests(void) {
     }
 #endif
 
+#if !defined(__powerpc__)
+    {
+        struct Struct_u32_Union_u32_u32u32 s = zig_ret_struct_u32_union_u32_u32u32();
+        assert_or_panic(s.a == 1);
+        assert_or_panic(s.b.c.d == 2);
+        assert_or_panic(s.b.c.e == 3);
+        zig_struct_u32_union_u32_u32u32(s);
+    }
+#endif
+
     {
         struct BigStruct s = {1, 2, 3, 4, 5};
         zig_big_struct(s);
@@ -2678,7 +2715,7 @@ void run_c_tests(void) {
     }
 #endif
 
-#if !defined __i386__ && !defined __arm__ && !defined __aarch64__ && \
+#if !defined __arm__ && !defined __aarch64__ && \
     !defined __mips__ && !defined __powerpc__ && !defined ZIG_RISCV64
     {
         struct MedStructInts s = {1, 2, 3};
diff --git a/test/c_abi/main.zig b/test/c_abi/main.zig
index fb5879338b..028156f35d 100644
--- a/test/c_abi/main.zig
+++ b/test/c_abi/main.zig
@@ -10,11 +10,11 @@ const builtin = @import("builtin");
 const print = std.debug.print;
 const expect = std.testing.expect;
 const expectEqual = std.testing.expectEqual;
-const has_i128 = builtin.cpu.arch != .x86 and !builtin.cpu.arch.isARM() and
+const have_i128 = builtin.cpu.arch != .x86 and !builtin.cpu.arch.isARM() and
     !builtin.cpu.arch.isMIPS() and !builtin.cpu.arch.isPPC();
 
-const has_f128 = builtin.cpu.arch.isX86() and !builtin.os.tag.isDarwin();
-const has_f80 = builtin.cpu.arch.isX86();
+const have_f128 = builtin.cpu.arch.isX86() and !builtin.os.tag.isDarwin();
+const have_f80 = builtin.cpu.arch.isX86();
 
 extern fn run_c_tests() void;
 
@@ -53,13 +53,13 @@ test "C ABI integers" {
     c_u16(0xfffe);
     c_u32(0xfffffffd);
     c_u64(0xfffffffffffffffc);
-    if (has_i128) c_struct_u128(.{ .value = 0xfffffffffffffffc });
+    if (have_i128) c_struct_u128(.{ .value = 0xfffffffffffffffc });
 
     c_i8(-1);
     c_i16(-2);
     c_i32(-3);
     c_i64(-4);
-    if (has_i128) c_struct_i128(.{ .value = -6 });
+    if (have_i128) c_struct_i128(.{ .value = -6 });
     c_five_integers(12, 34, 56, 78, 90);
 }
 
@@ -186,7 +186,6 @@ const complex_abi_compatible = builtin.cpu.arch != .x86 and !builtin.cpu.arch.is
 
 test "C ABI complex float" {
     if (!complex_abi_compatible) return error.SkipZigTest;
-    if (builtin.zig_backend == .stage2_llvm and builtin.cpu.arch == .x86_64) return error.SkipZigTest; // See https://github.com/ziglang/zig/issues/8465
 
     const a = ComplexFloat{ .real = 1.25, .imag = 2.6 };
     const b = ComplexFloat{ .real = 11.3, .imag = -1.5 };
@@ -401,6 +400,42 @@ test "C ABI struct f32 {f32,f32}" {
     c_struct_f32_f32f32(.{ .a = 1.0, .b = .{ .c = 2.0, .d = 3.0 } });
 }
 
+const Struct_u32_Union_u32_u32u32 = extern struct {
+    a: u32,
+    b: extern union {
+        c: extern struct {
+            d: u32,
+            e: u32,
+        },
+    },
+};
+
+export fn zig_ret_struct_u32_union_u32_u32u32() Struct_u32_Union_u32_u32u32 {
+    return .{ .a = 1, .b = .{ .c = .{ .d = 2, .e = 3 } } };
+}
+
+export fn zig_struct_u32_union_u32_u32u32(s: Struct_u32_Union_u32_u32u32) void {
+    expect(s.a == 1) catch @panic("test failure");
+    expect(s.b.c.d == 2) catch @panic("test failure");
+    expect(s.b.c.e == 3) catch @panic("test failure");
+}
+
+extern fn c_ret_struct_u32_union_u32_u32u32() Struct_u32_Union_u32_u32u32;
+
+extern fn c_struct_u32_union_u32_u32u32(Struct_u32_Union_u32_u32u32) void;
+
+test "C ABI struct{u32,union{u32,struct{u32,u32}}}" {
+    if (builtin.cpu.arch.isMIPS()) return error.SkipZigTest;
+    if (builtin.cpu.arch.isPPC()) return error.SkipZigTest;
+    if (builtin.cpu.arch.isPPC64()) return error.SkipZigTest;
+
+    const s = c_ret_struct_u32_union_u32_u32u32();
+    try expect(s.a == 1);
+    try expect(s.b.c.d == 2);
+    try expect(s.b.c.e == 3);
+    c_struct_u32_union_u32_u32u32(.{ .a = 1, .b = .{ .c = .{ .d = 2, .e = 3 } } });
+}
+
 const BigStruct = extern struct {
     a: u64,
     b: u64,
@@ -470,7 +505,6 @@ extern fn c_med_struct_mixed(MedStructMixed) void;
 extern fn c_ret_med_struct_mixed() MedStructMixed;
 
 test "C ABI medium struct of ints and floats" {
-    if (builtin.cpu.arch == .x86) return error.SkipZigTest;
     if (builtin.cpu.arch.isMIPS()) return error.SkipZigTest;
     if (builtin.cpu.arch.isPPC()) return error.SkipZigTest;
     if (builtin.cpu.arch.isPPC64()) return error.SkipZigTest;
@@ -538,7 +572,6 @@ extern fn c_med_struct_ints(MedStructInts) void;
 extern fn c_ret_med_struct_ints() MedStructInts;
 
 test "C ABI medium struct of ints" {
-    if (builtin.cpu.arch == .x86) return error.SkipZigTest;
     if (builtin.cpu.arch.isMIPS()) return error.SkipZigTest;
     if (builtin.cpu.arch.isPPC()) return error.SkipZigTest;
     if (builtin.cpu.arch.isPPC64()) return error.SkipZigTest;
@@ -600,7 +633,7 @@ export fn zig_big_packed_struct(x: BigPackedStruct) void {
 }
 
 test "C ABI big packed struct" {
-    if (!has_i128) return error.SkipZigTest;
+    if (!have_i128) return error.SkipZigTest;
 
     const s = BigPackedStruct{ .a = 1, .b = 2 };
     c_big_packed_struct(s);
@@ -943,7 +976,6 @@ extern fn c_float_array_struct(FloatArrayStruct) void;
 extern fn c_ret_float_array_struct() FloatArrayStruct;
 
 test "Float array like struct" {
-    if (builtin.cpu.arch == .x86 and builtin.mode != .Debug) return error.SkipZigTest;
     if (builtin.cpu.arch.isMIPS()) return error.SkipZigTest;
     if (builtin.cpu.arch.isPPC()) return error.SkipZigTest;
 
@@ -5318,7 +5350,6 @@ extern fn c_ptr_size_float_struct(Vector2) void;
 extern fn c_ret_ptr_size_float_struct() Vector2;
 
 test "C ABI pointer sized float struct" {
-    if (builtin.cpu.arch == .x86) return error.SkipZigTest;
     if (builtin.cpu.arch.isMIPS()) return error.SkipZigTest;
     if (builtin.cpu.arch.isRISCV()) return error.SkipZigTest;
     if (builtin.cpu.arch.isPPC()) return error.SkipZigTest;
@@ -5348,7 +5379,6 @@ test "DC: Zig passes to C" {
     try expectOk(c_assert_DC(.{ .v1 = -0.25, .v2 = 15 }));
 }
 test "DC: Zig returns to C" {
-    if (builtin.cpu.arch == .x86 and builtin.mode != .Debug) return error.SkipZigTest;
     if (builtin.cpu.arch.isMIPS() and builtin.mode != .Debug) return error.SkipZigTest;
     if (builtin.cpu.arch.isRISCV()) return error.SkipZigTest;
     if (builtin.cpu.arch.isPPC()) return error.SkipZigTest;
@@ -5363,7 +5393,6 @@ test "DC: C passes to Zig" {
     try expectOk(c_send_DC());
 }
 test "DC: C returns to Zig" {
-    if (builtin.cpu.arch == .x86 and builtin.mode != .Debug) return error.SkipZigTest;
     if (builtin.cpu.arch.isMIPS() and builtin.mode != .Debug) return error.SkipZigTest;
     if (builtin.cpu.arch.isRISCV()) return error.SkipZigTest;
     if (builtin.cpu.arch.isPPC()) return error.SkipZigTest;
@@ -5397,7 +5426,6 @@ test "CFF: Zig passes to C" {
     try expectOk(c_assert_CFF(.{ .v1 = 39, .v2 = 0.875, .v3 = 1.0 }));
 }
 test "CFF: Zig returns to C" {
-    if (builtin.cpu.arch == .x86 and builtin.mode != .Debug) return error.SkipZigTest;
     if (builtin.cpu.arch.isMIPS()) return error.SkipZigTest;
     if (builtin.cpu.arch.isPPC()) return error.SkipZigTest;
     if (builtin.cpu.arch.isPPC64()) return error.SkipZigTest;
@@ -5414,7 +5442,6 @@ test "CFF: C passes to Zig" {
     try expectOk(c_send_CFF());
 }
 test "CFF: C returns to Zig" {
-    if (builtin.cpu.arch == .x86 and builtin.mode != .Debug) return error.SkipZigTest;
     if (builtin.cpu.arch == .aarch64 and builtin.mode != .Debug) return error.SkipZigTest;
     if (builtin.cpu.arch.isRISCV() and builtin.mode != .Debug) return error.SkipZigTest;
     if (builtin.cpu.arch.isMIPS()) return error.SkipZigTest;
@@ -5442,28 +5469,24 @@ pub export fn zig_ret_CFF() CFF {
 const PD = extern struct { v1: ?*anyopaque, v2: f64 };
 
 test "PD: Zig passes to C" {
-    if (builtin.target.cpu.arch == .x86) return error.SkipZigTest;
     if (builtin.cpu.arch.isMIPS()) return error.SkipZigTest;
     if (builtin.cpu.arch.isPPC()) return error.SkipZigTest;
     if (builtin.cpu.arch.isPPC64()) return error.SkipZigTest;
     try expectOk(c_assert_PD(.{ .v1 = null, .v2 = 0.5 }));
 }
 test "PD: Zig returns to C" {
-    if (builtin.target.cpu.arch == .x86) return error.SkipZigTest;
     if (builtin.cpu.arch.isMIPS() and builtin.mode != .Debug) return error.SkipZigTest;
     if (builtin.cpu.arch.isPPC()) return error.SkipZigTest;
     if (builtin.cpu.arch.isPPC64()) return error.SkipZigTest;
     try expectOk(c_assert_ret_PD());
 }
 test "PD: C passes to Zig" {
-    if (builtin.target.cpu.arch == .x86) return error.SkipZigTest;
     if (builtin.cpu.arch.isMIPS()) return error.SkipZigTest;
     if (builtin.cpu.arch.isPPC()) return error.SkipZigTest;
     if (builtin.cpu.arch.isPPC64()) return error.SkipZigTest;
     try expectOk(c_send_PD());
 }
 test "PD: C returns to Zig" {
-    if (builtin.target.cpu.arch == .x86) return error.SkipZigTest;
     if (builtin.cpu.arch.isMIPS() and builtin.mode != .Debug) return error.SkipZigTest;
     if (builtin.cpu.arch.isPPC()) return error.SkipZigTest;
     if (builtin.cpu.arch.isPPC64()) return error.SkipZigTest;
@@ -5519,7 +5542,6 @@ const ByVal = extern struct {
 
 extern fn c_func_ptr_byval(*anyopaque, *anyopaque, ByVal, c_ulong, *anyopaque, c_ulong) void;
 test "C function that takes byval struct called via function pointer" {
-    if (builtin.cpu.arch == .x86 and builtin.mode != .Debug) return error.SkipZigTest;
     if (builtin.cpu.arch.isMIPS() and builtin.mode != .Debug) return error.SkipZigTest;
     if (builtin.cpu.arch.isPPC()) return error.SkipZigTest;
 
@@ -5551,7 +5573,6 @@ const f16_struct = extern struct {
 };
 extern fn c_f16_struct(f16_struct) f16_struct;
 test "f16 struct" {
-    if (builtin.target.cpu.arch == .x86) return error.SkipZigTest;
     if (builtin.target.cpu.arch.isMIPS()) return error.SkipZigTest;
     if (builtin.target.cpu.arch.isPPC()) return error.SkipZigTest;
     if (builtin.target.cpu.arch.isPPC()) return error.SkipZigTest;
@@ -5563,7 +5584,7 @@ test "f16 struct" {
 
 extern fn c_f80(f80) f80;
 test "f80 bare" {
-    if (!has_f80) return error.SkipZigTest;
+    if (!have_f80) return error.SkipZigTest;
 
     const a = c_f80(12.34);
     try expect(@as(f64, @floatCast(a)) == 56.78);
@@ -5574,9 +5595,7 @@ const f80_struct = extern struct {
 };
 extern fn c_f80_struct(f80_struct) f80_struct;
 test "f80 struct" {
-    if (!has_f80) return error.SkipZigTest;
-    if (builtin.target.cpu.arch == .x86) return error.SkipZigTest;
-    if (builtin.zig_backend == .stage2_llvm and builtin.mode != .Debug) return error.SkipZigTest;
+    if (!have_f80) return error.SkipZigTest;
 
     const a = c_f80_struct(.{ .a = 12.34 });
     try expect(@as(f64, @floatCast(a.a)) == 56.78);
@@ -5588,8 +5607,7 @@ const f80_extra_struct = extern struct {
 };
 extern fn c_f80_extra_struct(f80_extra_struct) f80_extra_struct;
 test "f80 extra struct" {
-    if (!has_f80) return error.SkipZigTest;
-    if (builtin.target.cpu.arch == .x86) return error.SkipZigTest;
+    if (!have_f80) return error.SkipZigTest;
 
     const a = c_f80_extra_struct(.{ .a = 12.34, .b = 42 });
     try expect(@as(f64, @floatCast(a.a)) == 56.78);
@@ -5598,7 +5616,7 @@ test "f80 extra struct" {
 
 extern fn c_f128(f128) f128;
 test "f128 bare" {
-    if (!has_f128) return error.SkipZigTest;
+    if (!have_f128) return error.SkipZigTest;
 
     const a = c_f128(12.34);
     try expect(@as(f64, @floatCast(a)) == 56.78);
@@ -5609,7 +5627,7 @@ const f128_struct = extern struct {
 };
 extern fn c_f128_struct(f128_struct) f128_struct;
 test "f128 struct" {
-    if (!has_f128) return error.SkipZigTest;
+    if (!have_f128) return error.SkipZigTest;
 
     const a = c_f128_struct(.{ .a = 12.34 });
     try expect(@as(f64, @floatCast(a.a)) == 56.78);
diff --git a/test/cases/compile_errors/invalid_func_for_callconv.zig b/test/cases/compile_errors/invalid_func_for_callconv.zig
new file mode 100644
index 0000000000..490b87bc4b
--- /dev/null
+++ b/test/cases/compile_errors/invalid_func_for_callconv.zig
@@ -0,0 +1,20 @@
+export fn interrupt_param1(_: u32) callconv(.Interrupt) void {}
+export fn interrupt_param2(_: *anyopaque, _: u32) callconv(.Interrupt) void {}
+export fn interrupt_param3(_: *anyopaque, _: u64, _: u32) callconv(.Interrupt) void {}
+export fn interrupt_ret(_: *anyopaque, _: u64) callconv(.Interrupt) u32 {
+    return 0;
+}
+
+export fn signal_param(_: u32) callconv(.Signal) void {}
+export fn signal_ret() callconv(.Signal) noreturn {}
+
+// error
+// backend=stage2
+// target=x86_64-linux
+// 
+// :1:28: error: first parameter of function with 'Interrupt' calling convention must be a pointer type
+// :2:43: error: second parameter of function with 'Interrupt' calling convention must be a 64-bit integer
+// :3:51: error: 'Interrupt' calling convention supports up to 2 parameters, found 3
+// :4:69: error: function with calling convention 'Interrupt' must return 'void' or 'noreturn'
+// :8:24: error: parameters are not allowed with 'Signal' calling convention
+// :9:34: error: callconv 'Signal' is only available on AVR, not x86_64
diff --git a/test/cases/compile_errors/runtime_@ptrFromInt_to_comptime_only_type.zig b/test/cases/compile_errors/runtime_@ptrFromInt_to_comptime_only_type.zig
new file mode 100644
index 0000000000..0c4e844e76
--- /dev/null
+++ b/test/cases/compile_errors/runtime_@ptrFromInt_to_comptime_only_type.zig
@@ -0,0 +1,16 @@
+const GuSettings = struct {
+    fin: ?fn (c_int) callconv(.C) void,
+};
+pub export fn callbackFin(id: c_int, arg: ?*anyopaque) void {
+    const settings: ?*GuSettings = @as(?*GuSettings, @ptrFromInt(@intFromPtr(arg)));
+    if (settings.?.fin != null) {
+        settings.?.fin.?(id & 0xffff);
+    }
+}
+
+// error
+// target=native
+//
+// :5:54: error: pointer to comptime-only type '?*tmp.GuSettings' must be comptime-known, but operand is runtime-known
+// :2:10: note: struct requires comptime because of this field
+// :2:10: note: use '*const fn (c_int) callconv(.C) void' for a function pointer type
diff --git a/test/cases/compile_errors/slice_end_index_undefined.zig b/test/cases/compile_errors/slice_end_index_undefined.zig
new file mode 100644
index 0000000000..151c156f18
--- /dev/null
+++ b/test/cases/compile_errors/slice_end_index_undefined.zig
@@ -0,0 +1,10 @@
+export fn a() void {
+    var array: [0]void = undefined;
+    _ = array[0..undefined];
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :3:18: error: use of undefined value here causes undefined behavior
diff --git a/test/link/elf.zig b/test/link/elf.zig
index d018d042e3..d97afd4d8f 100644
--- a/test/link/elf.zig
+++ b/test/link/elf.zig
@@ -61,6 +61,7 @@ pub fn testAll(b: *Build, build_opts: BuildOptions) *Step {
         elf_step.dependOn(testAbsSymbols(b, .{ .target = musl_target }));
         elf_step.dependOn(testCommonSymbols(b, .{ .target = musl_target }));
         elf_step.dependOn(testCommonSymbolsInArchive(b, .{ .target = musl_target }));
+        elf_step.dependOn(testCommentString(b, .{ .target = musl_target }));
         elf_step.dependOn(testEmptyObject(b, .{ .target = musl_target }));
         elf_step.dependOn(testEntryPoint(b, .{ .target = musl_target }));
         elf_step.dependOn(testGcSections(b, .{ .target = musl_target }));
@@ -72,6 +73,8 @@ pub fn testAll(b: *Build, build_opts: BuildOptions) *Step {
         elf_step.dependOn(testLinkingC(b, .{ .target = musl_target }));
         elf_step.dependOn(testLinkingCpp(b, .{ .target = musl_target }));
         elf_step.dependOn(testLinkingZig(b, .{ .target = musl_target }));
+        elf_step.dependOn(testMergeStrings(b, .{ .target = musl_target }));
+        elf_step.dependOn(testMergeStrings2(b, .{ .target = musl_target }));
         // https://github.com/ziglang/zig/issues/17451
         // elf_step.dependOn(testNoEhFrameHdr(b, .{ .target = musl_target }));
         elf_step.dependOn(testTlsStatic(b, .{ .target = musl_target }));
@@ -81,6 +84,7 @@ pub fn testAll(b: *Build, build_opts: BuildOptions) *Step {
         elf_step.dependOn(testAsNeeded(b, .{ .target = gnu_target }));
         // https://github.com/ziglang/zig/issues/17430
         // elf_step.dependOn(testCanonicalPlt(b, .{ .target = gnu_target }));
+        elf_step.dependOn(testCommentString(b, .{ .target = gnu_target }));
         elf_step.dependOn(testCopyrel(b, .{ .target = gnu_target }));
         // https://github.com/ziglang/zig/issues/17430
         // elf_step.dependOn(testCopyrelAlias(b, .{ .target = gnu_target }));
@@ -152,6 +156,8 @@ pub fn testAll(b: *Build, build_opts: BuildOptions) *Step {
     elf_step.dependOn(testThunks(b, .{ .target = aarch64_musl }));
 
     // x86_64 self-hosted backend
+    elf_step.dependOn(testCommentString(b, .{ .use_llvm = false, .target = default_target }));
+    elf_step.dependOn(testCommentStringStaticLib(b, .{ .use_llvm = false, .target = default_target }));
     elf_step.dependOn(testEmitRelocatable(b, .{ .use_llvm = false, .target = x86_64_musl }));
     elf_step.dependOn(testEmitStaticLibZig(b, .{ .use_llvm = false, .target = x86_64_musl }));
     elf_step.dependOn(testGcSectionsZig(b, .{ .use_llvm = false, .target = default_target }));
@@ -362,6 +368,36 @@ fn testCanonicalPlt(b: *Build, opts: Options) *Step {
     return test_step;
 }
 
+fn testCommentString(b: *Build, opts: Options) *Step {
+    const test_step = addTestStep(b, "comment-string", opts);
+
+    const exe = addExecutable(b, opts, .{ .name = "main", .zig_source_bytes = 
+    \\pub fn main() void {}
+    });
+
+    const check = exe.checkObject();
+    check.dumpSection(".comment");
+    check.checkContains("zig");
+    test_step.dependOn(&check.step);
+
+    return test_step;
+}
+
+fn testCommentStringStaticLib(b: *Build, opts: Options) *Step {
+    const test_step = addTestStep(b, "comment-string-static-lib", opts);
+
+    const lib = addStaticLibrary(b, opts, .{ .name = "lib", .zig_source_bytes = 
+    \\export fn foo() void {}
+    });
+
+    const check = lib.checkObject();
+    check.dumpSection(".comment");
+    check.checkContains("zig");
+    test_step.dependOn(&check.step);
+
+    return test_step;
+}
+
 fn testCommonSymbols(b: *Build, opts: Options) *Step {
     const test_step = addTestStep(b, "common-symbols", opts);
 
@@ -2267,6 +2303,125 @@ fn testLinkingZig(b: *Build, opts: Options) *Step {
     return test_step;
 }
 
+// Adapted from https://github.com/rui314/mold/blob/main/test/elf/mergeable-strings.sh
+fn testMergeStrings(b: *Build, opts: Options) *Step {
+    const test_step = addTestStep(b, "merge-strings", opts);
+
+    const obj1 = addObject(b, opts, .{ .name = "a.o" });
+    addCSourceBytes(obj1,
+        \\#include <uchar.h>
+        \\#include <wchar.h>
+        \\char *cstr1 = "foo";
+        \\wchar_t *wide1 = L"foo";
+        \\char16_t *utf16_1 = u"foo";
+        \\char32_t *utf32_1 = U"foo";
+    , &.{"-O2"});
+    obj1.linkLibC();
+
+    const obj2 = addObject(b, opts, .{ .name = "b.o" });
+    addCSourceBytes(obj2,
+        \\#include <stdio.h>
+        \\#include <assert.h>
+        \\#include <uchar.h>
+        \\#include <wchar.h>
+        \\extern char *cstr1;
+        \\extern wchar_t *wide1;
+        \\extern char16_t *utf16_1;
+        \\extern char32_t *utf32_1;
+        \\char *cstr2 = "foo";
+        \\wchar_t *wide2 = L"foo";
+        \\char16_t *utf16_2 = u"foo";
+        \\char32_t *utf32_2 = U"foo";
+        \\int main() {
+        \\ printf("%p %p %p %p %p %p %p %p\n",
+        \\ cstr1, cstr2, wide1, wide2, utf16_1, utf16_2, utf32_1, utf32_2);
+        \\  assert((void*)cstr1 ==   (void*)cstr2);
+        \\  assert((void*)wide1 ==   (void*)wide2);
+        \\  assert((void*)utf16_1 == (void*)utf16_2);
+        \\  assert((void*)utf32_1 == (void*)utf32_2);
+        \\  assert((void*)wide1 ==   (void*)utf32_1);
+        \\  assert((void*)cstr1 !=   (void*)wide1);
+        \\  assert((void*)cstr1 !=   (void*)utf32_1);
+        \\  assert((void*)wide1 !=   (void*)utf16_1);
+        \\}
+    , &.{"-O2"});
+    obj2.linkLibC();
+
+    const exe = addExecutable(b, opts, .{ .name = "main" });
+    exe.addObject(obj1);
+    exe.addObject(obj2);
+    exe.linkLibC();
+
+    const run = addRunArtifact(exe);
+    run.expectExitCode(0);
+    test_step.dependOn(&run.step);
+
+    return test_step;
+}
+
+fn testMergeStrings2(b: *Build, opts: Options) *Step {
+    const test_step = addTestStep(b, "merge-strings2", opts);
+
+    const obj1 = addObject(b, opts, .{ .name = "a", .zig_source_bytes = 
+    \\const std = @import("std");
+    \\export fn foo() void {
+    \\    var arr: [5:0]u16 = [_:0]u16{ 1, 2, 3, 4, 5 };
+    \\    const slice = std.mem.sliceTo(&arr, 3);
+    \\    std.testing.expectEqualSlices(u16, arr[0..2], slice) catch unreachable;
+    \\}
+    });
+
+    const obj2 = addObject(b, opts, .{ .name = "b", .zig_source_bytes = 
+    \\const std = @import("std");
+    \\extern fn foo() void;
+    \\pub fn main() void {
+    \\    foo();
+    \\    var arr: [5:0]u16 = [_:0]u16{ 5, 4, 3, 2, 1 };
+    \\    const slice = std.mem.sliceTo(&arr, 3);
+    \\    std.testing.expectEqualSlices(u16, arr[0..2], slice) catch unreachable;
+    \\}
+    });
+
+    {
+        const exe = addExecutable(b, opts, .{ .name = "main1" });
+        exe.addObject(obj1);
+        exe.addObject(obj2);
+
+        const run = addRunArtifact(exe);
+        run.expectExitCode(0);
+        test_step.dependOn(&run.step);
+
+        const check = exe.checkObject();
+        check.dumpSection(".rodata.str");
+        check.checkContains("\x01\x00\x02\x00\x03\x00\x04\x00\x05\x00\x00\x00");
+        check.dumpSection(".rodata.str");
+        check.checkContains("\x05\x00\x04\x00\x03\x00\x02\x00\x01\x00\x00\x00");
+        test_step.dependOn(&check.step);
+    }
+
+    {
+        const obj3 = addObject(b, opts, .{ .name = "c" });
+        obj3.addObject(obj1);
+        obj3.addObject(obj2);
+
+        const exe = addExecutable(b, opts, .{ .name = "main2" });
+        exe.addObject(obj3);
+
+        const run = addRunArtifact(exe);
+        run.expectExitCode(0);
+        test_step.dependOn(&run.step);
+
+        const check = exe.checkObject();
+        check.dumpSection(".rodata.str");
+        check.checkContains("\x01\x00\x02\x00\x03\x00\x04\x00\x05\x00\x00\x00");
+        check.dumpSection(".rodata.str");
+        check.checkContains("\x05\x00\x04\x00\x03\x00\x02\x00\x01\x00\x00\x00");
+        test_step.dependOn(&check.step);
+    }
+
+    return test_step;
+}
+
 fn testNoEhFrameHdr(b: *Build, opts: Options) *Step {
     const test_step = addTestStep(b, "no-eh-frame-hdr", opts);
 
@@ -2528,6 +2683,33 @@ fn testRelocatableEhFrame(b: *Build, opts: Options) *Step {
     return test_step;
 }
 
+// Adapted from https://github.com/rui314/mold/blob/main/test/elf/relocatable-mergeable-sections.sh
+fn testRelocatableMergeStrings(b: *Build, opts: Options) *Step {
+    const test_step = addTestStep(b, "relocatable-merge-strings", opts);
+
+    const obj1 = addObject(b, opts, .{ .name = "a", .asm_source_bytes = 
+    \\.section .rodata.str1.1,"aMS",@progbits,1
+    \\val1:
+    \\.ascii "Hello \0"
+    \\.section .rodata.str1.1,"aMS",@progbits,1
+    \\val5:
+    \\.ascii "World \0"
+    \\.section .rodata.str1.1,"aMS",@progbits,1
+    \\val7:
+    \\.ascii "Hello \0"
+    });
+
+    const obj2 = addObject(b, opts, .{ .name = "b" });
+    obj2.addObject(obj1);
+
+    const check = obj2.checkObject();
+    check.dumpSection(".rodata.str1.1");
+    check.checkExact("Hello \x00World \x00");
+    test_step.dependOn(&check.step);
+
+    return test_step;
+}
+
 fn testRelocatableNoEhFrame(b: *Build, opts: Options) *Step {
     const test_step = addTestStep(b, "relocatable-no-eh-frame", opts);
 
diff --git a/test/link/glibc_compat/glibc_runtime_check.zig b/test/link/glibc_compat/glibc_runtime_check.zig
index 3dc1548379..5a925d8583 100644
--- a/test/link/glibc_compat/glibc_runtime_check.zig
+++ b/test/link/glibc_compat/glibc_runtime_check.zig
@@ -91,7 +91,7 @@ fn checkStrlcpy() !void {
 fn checkStrlcpy_v2_38() !void {
     var buf: [99]u8 = undefined;
     const used = c_string.strlcpy(&buf, "strlcpy works!", buf.len);
-    assert(used == 15);
+    assert(used == 14);
 }
 
 // atexit is part of libc_nonshared, so ensure its linked in correctly
diff --git a/test/link/link.zig b/test/link/link.zig
index 2678b2cf84..8d13368aed 100644
--- a/test/link/link.zig
+++ b/test/link/link.zig
@@ -1,21 +1,3 @@
-pub fn build(b: *Build) void {
-    const test_step = b.step("test-link", "Run link tests");
-    b.default_step = test_step;
-
-    const has_macos_sdk = b.option(bool, "has_macos_sdk", "whether the host provides a macOS SDK in system path");
-    const has_ios_sdk = b.option(bool, "has_ios_sdk", "whether the host provides a iOS SDK in system path");
-    const has_symlinks_windows = b.option(bool, "has_symlinks_windows", "whether the host is windows and has symlinks enabled");
-
-    const build_opts: BuildOptions = .{
-        .has_macos_sdk = has_macos_sdk orelse false,
-        .has_ios_sdk = has_ios_sdk orelse false,
-        .has_symlinks_windows = has_symlinks_windows orelse false,
-    };
-
-    test_step.dependOn(@import("elf.zig").testAll(b, build_opts));
-    test_step.dependOn(@import("macho.zig").testAll(b, build_opts));
-}
-
 pub const BuildOptions = struct {
     has_macos_sdk: bool,
     has_ios_sdk: bool,
diff --git a/test/standalone/build.zig.zon b/test/standalone/build.zig.zon
index a307c0a528..7ddde1611a 100644
--- a/test/standalone/build.zig.zon
+++ b/test/standalone/build.zig.zon
@@ -107,6 +107,9 @@
         .windows_argv = .{
             .path = "windows_argv",
         },
+        .windows_bat_args = .{
+            .path = "windows_bat_args",
+        },
         .self_exe_symlink = .{
             .path = "self_exe_symlink",
         },
diff --git a/test/standalone/windows_bat_args/build.zig b/test/standalone/windows_bat_args/build.zig
new file mode 100644
index 0000000000..1d0a82b920
--- /dev/null
+++ b/test/standalone/windows_bat_args/build.zig
@@ -0,0 +1,58 @@
+const std = @import("std");
+const builtin = @import("builtin");
+
+pub fn build(b: *std.Build) !void {
+    const test_step = b.step("test", "Test it");
+    b.default_step = test_step;
+
+    const optimize: std.builtin.OptimizeMode = .Debug;
+    const target = b.host;
+
+    if (builtin.os.tag != .windows) return;
+
+    const echo_args = b.addExecutable(.{
+        .name = "echo-args",
+        .root_source_file = b.path("echo-args.zig"),
+        .optimize = optimize,
+        .target = target,
+    });
+
+    const test_exe = b.addExecutable(.{
+        .name = "test",
+        .root_source_file = b.path("test.zig"),
+        .optimize = optimize,
+        .target = target,
+    });
+
+    const run = b.addRunArtifact(test_exe);
+    run.addArtifactArg(echo_args);
+    run.expectExitCode(0);
+    run.skip_foreign_checks = true;
+
+    test_step.dependOn(&run.step);
+
+    const fuzz = b.addExecutable(.{
+        .name = "fuzz",
+        .root_source_file = b.path("fuzz.zig"),
+        .optimize = optimize,
+        .target = target,
+    });
+
+    const fuzz_max_iterations = b.option(u64, "iterations", "The max fuzz iterations (default: 100)") orelse 100;
+    const fuzz_iterations_arg = std.fmt.allocPrint(b.allocator, "{}", .{fuzz_max_iterations}) catch @panic("oom");
+
+    const fuzz_seed = b.option(u64, "seed", "Seed to use for the PRNG (default: random)") orelse seed: {
+        var buf: [8]u8 = undefined;
+        try std.posix.getrandom(&buf);
+        break :seed std.mem.readInt(u64, &buf, builtin.cpu.arch.endian());
+    };
+    const fuzz_seed_arg = std.fmt.allocPrint(b.allocator, "{}", .{fuzz_seed}) catch @panic("oom");
+
+    const fuzz_run = b.addRunArtifact(fuzz);
+    fuzz_run.addArtifactArg(echo_args);
+    fuzz_run.addArgs(&.{ fuzz_iterations_arg, fuzz_seed_arg });
+    fuzz_run.expectExitCode(0);
+    fuzz_run.skip_foreign_checks = true;
+
+    test_step.dependOn(&fuzz_run.step);
+}
diff --git a/test/standalone/windows_bat_args/echo-args.zig b/test/standalone/windows_bat_args/echo-args.zig
new file mode 100644
index 0000000000..2552045aed
--- /dev/null
+++ b/test/standalone/windows_bat_args/echo-args.zig
@@ -0,0 +1,14 @@
+const std = @import("std");
+
+pub fn main() !void {
+    var arena_state = std.heap.ArenaAllocator.init(std.heap.page_allocator);
+    defer arena_state.deinit();
+    const arena = arena_state.allocator();
+
+    const stdout = std.io.getStdOut().writer();
+    var args = try std.process.argsAlloc(arena);
+    for (args[1..], 1..) |arg, i| {
+        try stdout.writeAll(arg);
+        if (i != args.len - 1) try stdout.writeByte('\x00');
+    }
+}
diff --git a/test/standalone/windows_bat_args/fuzz.zig b/test/standalone/windows_bat_args/fuzz.zig
new file mode 100644
index 0000000000..6908f66a06
--- /dev/null
+++ b/test/standalone/windows_bat_args/fuzz.zig
@@ -0,0 +1,160 @@
+const std = @import("std");
+const builtin = @import("builtin");
+const Allocator = std.mem.Allocator;
+
+pub fn main() anyerror!void {
+    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+    defer if (gpa.deinit() == .leak) @panic("found memory leaks");
+    const allocator = gpa.allocator();
+
+    var it = try std.process.argsWithAllocator(allocator);
+    defer it.deinit();
+    _ = it.next() orelse unreachable; // skip binary name
+    const child_exe_path = it.next() orelse unreachable;
+
+    const iterations: u64 = iterations: {
+        const arg = it.next() orelse "0";
+        break :iterations try std.fmt.parseUnsigned(u64, arg, 10);
+    };
+
+    var rand_seed = false;
+    const seed: u64 = seed: {
+        const seed_arg = it.next() orelse {
+            rand_seed = true;
+            var buf: [8]u8 = undefined;
+            try std.posix.getrandom(&buf);
+            break :seed std.mem.readInt(u64, &buf, builtin.cpu.arch.endian());
+        };
+        break :seed try std.fmt.parseUnsigned(u64, seed_arg, 10);
+    };
+    var random = std.rand.DefaultPrng.init(seed);
+    const rand = random.random();
+
+    // If the seed was not given via the CLI, then output the
+    // randomly chosen seed so that this run can be reproduced
+    if (rand_seed) {
+        std.debug.print("rand seed: {}\n", .{seed});
+    }
+
+    var tmp = std.testing.tmpDir(.{});
+    defer tmp.cleanup();
+
+    try tmp.dir.setAsCwd();
+    defer tmp.parent_dir.setAsCwd() catch {};
+
+    var buf = try std.ArrayList(u8).initCapacity(allocator, 128);
+    defer buf.deinit();
+    try buf.appendSlice("@echo off\n");
+    try buf.append('"');
+    try buf.appendSlice(child_exe_path);
+    try buf.append('"');
+    const preamble_len = buf.items.len;
+
+    try buf.appendSlice(" %*");
+    try tmp.dir.writeFile("args1.bat", buf.items);
+    buf.shrinkRetainingCapacity(preamble_len);
+
+    try buf.appendSlice(" %1 %2 %3 %4 %5 %6 %7 %8 %9");
+    try tmp.dir.writeFile("args2.bat", buf.items);
+    buf.shrinkRetainingCapacity(preamble_len);
+
+    try buf.appendSlice(" \"%~1\" \"%~2\" \"%~3\" \"%~4\" \"%~5\" \"%~6\" \"%~7\" \"%~8\" \"%~9\"");
+    try tmp.dir.writeFile("args3.bat", buf.items);
+    buf.shrinkRetainingCapacity(preamble_len);
+
+    var i: u64 = 0;
+    while (iterations == 0 or i < iterations) {
+        const rand_arg = try randomArg(allocator, rand);
+        defer allocator.free(rand_arg);
+
+        try testExec(allocator, &.{rand_arg}, null);
+
+        i += 1;
+    }
+}
+
+fn testExec(allocator: std.mem.Allocator, args: []const []const u8, env: ?*std.process.EnvMap) !void {
+    try testExecBat(allocator, "args1.bat", args, env);
+    try testExecBat(allocator, "args2.bat", args, env);
+    try testExecBat(allocator, "args3.bat", args, env);
+}
+
+fn testExecBat(allocator: std.mem.Allocator, bat: []const u8, args: []const []const u8, env: ?*std.process.EnvMap) !void {
+    var argv = try std.ArrayList([]const u8).initCapacity(allocator, 1 + args.len);
+    defer argv.deinit();
+    argv.appendAssumeCapacity(bat);
+    argv.appendSliceAssumeCapacity(args);
+
+    const can_have_trailing_empty_args = std.mem.eql(u8, bat, "args3.bat");
+
+    const result = try std.ChildProcess.run(.{
+        .allocator = allocator,
+        .env_map = env,
+        .argv = argv.items,
+    });
+    defer allocator.free(result.stdout);
+    defer allocator.free(result.stderr);
+
+    try std.testing.expectEqualStrings("", result.stderr);
+    var it = std.mem.splitScalar(u8, result.stdout, '\x00');
+    var i: usize = 0;
+    while (it.next()) |actual_arg| {
+        if (i >= args.len and can_have_trailing_empty_args) {
+            try std.testing.expectEqualStrings("", actual_arg);
+            continue;
+        }
+        const expected_arg = args[i];
+        try std.testing.expectEqualSlices(u8, expected_arg, actual_arg);
+        i += 1;
+    }
+}
+
+fn randomArg(allocator: Allocator, rand: std.rand.Random) ![]const u8 {
+    const Choice = enum {
+        backslash,
+        quote,
+        space,
+        control,
+        printable,
+        surrogate_half,
+        non_ascii,
+    };
+
+    const choices = rand.uintAtMostBiased(u16, 256);
+    var buf = try std.ArrayList(u8).initCapacity(allocator, choices);
+    errdefer buf.deinit();
+
+    var last_codepoint: u21 = 0;
+    for (0..choices) |_| {
+        const choice = rand.enumValue(Choice);
+        const codepoint: u21 = switch (choice) {
+            .backslash => '\\',
+            .quote => '"',
+            .space => ' ',
+            .control => switch (rand.uintAtMostBiased(u8, 0x21)) {
+                // NUL/CR/LF can't roundtrip
+                '\x00', '\r', '\n' => ' ',
+                0x21 => '\x7F',
+                else => |b| b,
+            },
+            .printable => '!' + rand.uintAtMostBiased(u8, '~' - '!'),
+            .surrogate_half => rand.intRangeAtMostBiased(u16, 0xD800, 0xDFFF),
+            .non_ascii => rand.intRangeAtMostBiased(u21, 0x80, 0x10FFFF),
+        };
+        // Ensure that we always return well-formed WTF-8.
+        // Instead of concatenating to ensure well-formed WTF-8,
+        // we just skip encoding the low surrogate.
+        if (std.unicode.isSurrogateCodepoint(last_codepoint) and std.unicode.isSurrogateCodepoint(codepoint)) {
+            if (std.unicode.utf16IsHighSurrogate(@intCast(last_codepoint)) and std.unicode.utf16IsLowSurrogate(@intCast(codepoint))) {
+                continue;
+            }
+        }
+        try buf.ensureUnusedCapacity(4);
+        const unused_slice = buf.unusedCapacitySlice();
+        const len = std.unicode.wtf8Encode(codepoint, unused_slice) catch unreachable;
+        buf.items.len += len;
+        last_codepoint = codepoint;
+    }
+
+    return buf.toOwnedSlice();
+}
diff --git a/test/standalone/windows_bat_args/test.zig b/test/standalone/windows_bat_args/test.zig
new file mode 100644
index 0000000000..8dc27b14c9
--- /dev/null
+++ b/test/standalone/windows_bat_args/test.zig
@@ -0,0 +1,132 @@
+const std = @import("std");
+
+pub fn main() anyerror!void {
+    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+    defer if (gpa.deinit() == .leak) @panic("found memory leaks");
+    const allocator = gpa.allocator();
+
+    var it = try std.process.argsWithAllocator(allocator);
+    defer it.deinit();
+    _ = it.next() orelse unreachable; // skip binary name
+    const child_exe_path = it.next() orelse unreachable;
+
+    var tmp = std.testing.tmpDir(.{});
+    defer tmp.cleanup();
+
+    try tmp.dir.setAsCwd();
+    defer tmp.parent_dir.setAsCwd() catch {};
+
+    var buf = try std.ArrayList(u8).initCapacity(allocator, 128);
+    defer buf.deinit();
+    try buf.appendSlice("@echo off\n");
+    try buf.append('"');
+    try buf.appendSlice(child_exe_path);
+    try buf.append('"');
+    const preamble_len = buf.items.len;
+
+    try buf.appendSlice(" %*");
+    try tmp.dir.writeFile("args1.bat", buf.items);
+    buf.shrinkRetainingCapacity(preamble_len);
+
+    try buf.appendSlice(" %1 %2 %3 %4 %5 %6 %7 %8 %9");
+    try tmp.dir.writeFile("args2.bat", buf.items);
+    buf.shrinkRetainingCapacity(preamble_len);
+
+    try buf.appendSlice(" \"%~1\" \"%~2\" \"%~3\" \"%~4\" \"%~5\" \"%~6\" \"%~7\" \"%~8\" \"%~9\"");
+    try tmp.dir.writeFile("args3.bat", buf.items);
+    buf.shrinkRetainingCapacity(preamble_len);
+
+    // Test cases are from https://github.com/rust-lang/rust/blob/master/tests/ui/std/windows-bat-args.rs
+    try testExecError(error.InvalidBatchScriptArg, allocator, &.{"\x00"});
+    try testExecError(error.InvalidBatchScriptArg, allocator, &.{"\n"});
+    try testExecError(error.InvalidBatchScriptArg, allocator, &.{"\r"});
+    try testExec(allocator, &.{ "a", "b" }, null);
+    try testExec(allocator, &.{ "c is for cat", "d is for dog" }, null);
+    try testExec(allocator, &.{ "\"", " \"" }, null);
+    try testExec(allocator, &.{ "\\", "\\" }, null);
+    try testExec(allocator, &.{">file.txt"}, null);
+    try testExec(allocator, &.{"whoami.exe"}, null);
+    try testExec(allocator, &.{"&a.exe"}, null);
+    try testExec(allocator, &.{"&echo hello "}, null);
+    try testExec(allocator, &.{ "&echo hello", "&whoami", ">file.txt" }, null);
+    try testExec(allocator, &.{"!TMP!"}, null);
+    try testExec(allocator, &.{"key=value"}, null);
+    try testExec(allocator, &.{"\"key=value\""}, null);
+    try testExec(allocator, &.{"key = value"}, null);
+    try testExec(allocator, &.{"key=[\"value\"]"}, null);
+    try testExec(allocator, &.{ "", "a=b" }, null);
+    try testExec(allocator, &.{"key=\"foo bar\""}, null);
+    try testExec(allocator, &.{"key=[\"my_value]"}, null);
+    try testExec(allocator, &.{"key=[\"my_value\",\"other-value\"]"}, null);
+    try testExec(allocator, &.{"key\\=value"}, null);
+    try testExec(allocator, &.{"key=\"&whoami\""}, null);
+    try testExec(allocator, &.{"key=\"value\"=5"}, null);
+    try testExec(allocator, &.{"key=[\">file.txt\"]"}, null);
+    try testExec(allocator, &.{"%hello"}, null);
+    try testExec(allocator, &.{"%PATH%"}, null);
+    try testExec(allocator, &.{"%%cd:~,%"}, null);
+    try testExec(allocator, &.{"%PATH%PATH%"}, null);
+    try testExec(allocator, &.{"\">file.txt"}, null);
+    try testExec(allocator, &.{"abc\"&echo hello"}, null);
+    try testExec(allocator, &.{"123\">file.txt"}, null);
+    try testExec(allocator, &.{"\"&echo hello&whoami.exe"}, null);
+    try testExec(allocator, &.{ "\"hello^\"world\"", "hello &echo oh no >file.txt" }, null);
+    try testExec(allocator, &.{"&whoami.exe"}, null);
+
+    var env = env: {
+        var env = try std.process.getEnvMap(allocator);
+        errdefer env.deinit();
+        // No escaping
+        try env.put("FOO", "123");
+        // Some possible escaping of %FOO% that could be expanded
+        // when escaping cmd.exe meta characters with ^
+        try env.put("FOO^", "123"); // only escaping %
+        try env.put("^F^O^O^", "123"); // escaping every char
+        break :env env;
+    };
+    defer env.deinit();
+    try testExec(allocator, &.{"%FOO%"}, &env);
+
+    // Ensure that none of the `>file.txt`s have caused file.txt to be created
+    try std.testing.expectError(error.FileNotFound, tmp.dir.access("file.txt", .{}));
+}
+
+fn testExecError(err: anyerror, allocator: std.mem.Allocator, args: []const []const u8) !void {
+    return std.testing.expectError(err, testExec(allocator, args, null));
+}
+
+fn testExec(allocator: std.mem.Allocator, args: []const []const u8, env: ?*std.process.EnvMap) !void {
+    try testExecBat(allocator, "args1.bat", args, env);
+    try testExecBat(allocator, "args2.bat", args, env);
+    try testExecBat(allocator, "args3.bat", args, env);
+}
+
+fn testExecBat(allocator: std.mem.Allocator, bat: []const u8, args: []const []const u8, env: ?*std.process.EnvMap) !void {
+    var argv = try std.ArrayList([]const u8).initCapacity(allocator, 1 + args.len);
+    defer argv.deinit();
+    argv.appendAssumeCapacity(bat);
+    argv.appendSliceAssumeCapacity(args);
+
+    const can_have_trailing_empty_args = std.mem.eql(u8, bat, "args3.bat");
+
+    const result = try std.ChildProcess.run(.{
+        .allocator = allocator,
+        .env_map = env,
+        .argv = argv.items,
+    });
+    defer allocator.free(result.stdout);
+    defer allocator.free(result.stderr);
+
+    try std.testing.expectEqualStrings("", result.stderr);
+    var it = std.mem.splitScalar(u8, result.stdout, '\x00');
+    var i: usize = 0;
+    while (it.next()) |actual_arg| {
+        if (i >= args.len and can_have_trailing_empty_args) {
+            try std.testing.expectEqualStrings("", actual_arg);
+            continue;
+        }
+        const expected_arg = args[i];
+        try std.testing.expectEqualStrings(expected_arg, actual_arg);
+        i += 1;
+    }
+}
diff --git a/test/standalone/windows_resources/build.zig b/test/standalone/windows_resources/build.zig
index 6a72dee2a6..15130d3b87 100644
--- a/test/standalone/windows_resources/build.zig
+++ b/test/standalone/windows_resources/build.zig
@@ -10,11 +10,13 @@ pub fn build(b: *std.Build) void {
         .abi = .gnu,
     });
 
-    add(b, b.host, .any, test_step);
-    add(b, target, .any, test_step);
+    const generated_h_step = b.addWriteFile("generated.h", "#define GENERATED_DEFINE \"foo\"");
 
-    add(b, b.host, .gnu, test_step);
-    add(b, target, .gnu, test_step);
+    add(b, b.host, .any, test_step, generated_h_step);
+    add(b, target, .any, test_step, generated_h_step);
+
+    add(b, b.host, .gnu, test_step, generated_h_step);
+    add(b, target, .gnu, test_step, generated_h_step);
 }
 
 fn add(
@@ -22,6 +24,7 @@ fn add(
     target: std.Build.ResolvedTarget,
     rc_includes: enum { any, gnu },
     test_step: *std.Build.Step,
+    generated_h_step: *std.Build.Step.WriteFile,
 ) void {
     const exe = b.addExecutable(.{
         .name = "zig_resource_test",
@@ -32,6 +35,9 @@ fn add(
     exe.addWin32ResourceFile(.{
         .file = b.path("res/zig.rc"),
         .flags = &.{"/c65001"}, // UTF-8 code page
+        .include_paths = &.{
+            .{ .generated = &generated_h_step.generated_directory },
+        },
     });
     exe.rc_includes = switch (rc_includes) {
         .any => .any,
diff --git a/test/standalone/windows_resources/res/zig.rc b/test/standalone/windows_resources/res/zig.rc
index 88503a0f6a..ae2ad99027 100644
--- a/test/standalone/windows_resources/res/zig.rc
+++ b/test/standalone/windows_resources/res/zig.rc
@@ -1,3 +1,7 @@
+// This include file is generated via build.zig, and it #defines GENERATED_DEFINE
+#include "generated.h"
+FOO RCDATA { GENERATED_DEFINE }
+
 #define ICO_ID 1
 
 // Nothing from windows.h is used in this .rc file,