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std.Io.File.MemoryMap: add some alignment type safety

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This commit is contained in:
Andrew Kelley 2026-01-14 19:30:37 -08:00
parent 4821898432
commit eb163361d9
2 changed files with 16 additions and 12 deletions
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6
lib/std/Io/File/MemoryMap.zig
View file

@ -13,9 +13,9 @@ file: File,
/// Byte index inside `file` where `memory` starts. Page-aligned.
offset: u64,
/// Memory that may or may not remain consistent with file contents. Use `read`
/// and `write` to ensure synchronization points. Pointer is page-aligned but
/// length is not.
memory: []u8,
/// and `write` to ensure synchronization points. Length has no alignment
/// requirement.
memory: []align(std.heap.page_size_min) u8,
/// Tells whether it is memory-mapped or file operations. On Windows this also
/// has a section handle.
section: ?Section,

22
lib/std/Io/Threaded.zig
View file

@ -16198,7 +16198,7 @@ fn fileMemoryMapCreate(
return .{
.file = file,
.offset = offset,
.memory = memory,
.memory = @alignCast(memory),
.section = null,
};
}
@ -16283,7 +16283,7 @@ fn createFileMap(
return .{
.file = file,
.offset = offset,
.memory = contents_ptr.?[0..contents_len],
.memory = @alignCast(contents_ptr.?[0..contents_len]),
.section = section,
};
} else if (have_mmap) {
@ -16297,6 +16297,8 @@ fn createFileMap(
.POPULATE = populate,
};
const page_align = std.heap.page_size_min;
const contents = while (true) {
const syscall: Syscall = try .start();
const casted_offset = std.math.cast(i64, offset) orelse return error.Unseekable;
@ -16304,13 +16306,13 @@ fn createFileMap(
syscall.finish();
const err: posix.E = if (builtin.link_libc) e: {
if (rc != std.c.MAP_FAILED) {
break @as([*]u8, @ptrCast(@alignCast(rc)))[0..aligned_len];
break @as([*]align(page_align) u8, @ptrCast(@alignCast(rc)))[0..aligned_len];
}
break :e @enumFromInt(posix.system._errno().*);
} else e: {
const err = posix.errno(rc);
if (err == .SUCCESS) {
break @as([*]u8, @ptrFromInt(rc))[0..aligned_len];
break @as([*]align(page_align) u8, @ptrFromInt(rc))[0..aligned_len];
}
break :e err;
};
@ -16375,6 +16377,7 @@ fn fileMemoryMapSetLength(
const t: *Threaded = @ptrCast(@alignCast(userdata));
const page_size = std.heap.pageSize();
const alignment: Alignment = .fromByteUnits(page_size);
const page_align = std.heap.page_size_min;
if (mm.section) |section| {
if (alignment.forward(new_len) == alignment.forward(mm.memory.len)) {
@ -16395,11 +16398,11 @@ fn fileMemoryMapSetLength(
const rc = posix.system.mremap(mm.memory.ptr, mm.memory.len, new_len, flags, addr_hint);
syscall.finish();
const err: posix.E = if (builtin.link_libc) e: {
if (rc != std.c.MAP_FAILED) break @as([*]u8, @ptrCast(@alignCast(rc)))[0..new_len];
if (rc != std.c.MAP_FAILED) break @as([*]align(page_align) u8, @ptrCast(@alignCast(rc)))[0..new_len];
break :e @enumFromInt(posix.system._errno().*);
} else e: {
const err = posix.errno(rc);
if (err == .SUCCESS) break @as([*]u8, @ptrFromInt(rc))[0..new_len];
if (err == .SUCCESS) break @as([*]align(page_align) u8, @ptrFromInt(rc))[0..new_len];
break :e err;
};
switch (err) {
@ -16418,10 +16421,11 @@ fn fileMemoryMapSetLength(
} else {
const gpa = t.allocator;
if (gpa.rawRemap(mm.memory, alignment, new_len, @returnAddress())) |new_ptr| {
mm.memory = new_ptr[0..new_len];
mm.memory = @alignCast(new_ptr[0..new_len]);
} else {
const new_ptr = gpa.rawAlloc(new_len, alignment, @returnAddress()) orelse
return error.OutOfMemory;
const new_ptr: [*]align(page_align) u8 = @alignCast(
gpa.rawAlloc(new_len, alignment, @returnAddress()) orelse return error.OutOfMemory,
);
const copy_len = @min(new_len, mm.memory.len);
@memcpy(new_ptr[0..copy_len], mm.memory[0..copy_len]);
mm.memory = new_ptr[0..new_len];