From 2e35fdd032035203b588fa229585c3ee6702f2d4 Mon Sep 17 00:00:00 2001
From: tjog <28024277+tjog@users.noreply.github.com>
Date: Mon, 21 Apr 2025 17:44:31 +0200
Subject: [PATCH] fuzz: fix expected section start/end symbol name on MacOS
 when linking libfuzzer

Not only is the section name when adding the sancov variables different.

The linker symbol ending up in the binary is also different.

Reference: https://github.com/llvm/llvm-project/blob/60105ac6bab130c2694fc7f5b7b6a5fddaaab752/llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp#L1076-L1104
---
 lib/fuzzer.zig | 37 ++++++++++++++++++++++++++-----------
 1 file changed, 26 insertions(+), 11 deletions(-)

diff --git a/lib/fuzzer.zig b/lib/fuzzer.zig
index 92b621d07f..115b5415a6 100644
--- a/lib/fuzzer.zig
+++ b/lib/fuzzer.zig
@@ -468,27 +468,42 @@ export fn fuzzer_init(cache_dir_struct: Fuzzer.Slice) void {
     // Linkers are expected to automatically add `__start_<section>` and
     // `__stop_<section>` symbols when section names are valid C identifiers.
 
-    const pc_counters_start = @extern([*]u8, .{
-        .name = "__start___sancov_cntrs",
-        .linkage = .weak,
-    }) orelse fatal("missing __start___sancov_cntrs symbol", .{});
+    const ofmt = builtin.object_format;
 
-    const pc_counters_end = @extern([*]u8, .{
-        .name = "__stop___sancov_cntrs",
+    const start_symbol_prefix: []const u8 = if (ofmt == .macho)
+        "\x01section$start$__DATA$__"
+    else
+        "__start___";
+    const end_symbol_prefix: []const u8 = if (ofmt == .macho)
+        "\x01section$end$__DATA$__"
+    else
+        "__end___";
+
+    const pc_counters_start_name = start_symbol_prefix ++ "sancov_cntrs";
+    const pc_counters_start = @extern([*]u8, .{
+        .name = pc_counters_start_name,
         .linkage = .weak,
-    }) orelse fatal("missing __stop___sancov_cntrs symbol", .{});
+    }) orelse fatal("missing {s} symbol", .{pc_counters_start_name});
+
+    const pc_counters_end_name = end_symbol_prefix ++ "sancov_cntrs";
+    const pc_counters_end = @extern([*]u8, .{
+        .name = pc_counters_end_name,
+        .linkage = .weak,
+    }) orelse fatal("missing {s} symbol", .{pc_counters_end_name});
 
     const pc_counters = pc_counters_start[0 .. pc_counters_end - pc_counters_start];
 
+    const pcs_start_name = start_symbol_prefix ++ "sancov_pcs1";
     const pcs_start = @extern([*]usize, .{
-        .name = "__start___sancov_pcs1",
+        .name = pcs_start_name,
         .linkage = .weak,
-    }) orelse fatal("missing __start___sancov_pcs1 symbol", .{});
+    }) orelse fatal("missing {s} symbol", .{pcs_start_name});
 
+    const pcs_end_name = end_symbol_prefix ++ "sancov_pcs1";
     const pcs_end = @extern([*]usize, .{
-        .name = "__stop___sancov_pcs1",
+        .name = pcs_end_name,
         .linkage = .weak,
-    }) orelse fatal("missing __stop___sancov_pcs1 symbol", .{});
+    }) orelse fatal("missing {s} symbol", .{pcs_end_name});
 
     const pcs = pcs_start[0 .. pcs_end - pcs_start];