From 3ed159964a34bb73ba484bae95c714449c16b0fc Mon Sep 17 00:00:00 2001
From: tjog <28024277+tjog@users.noreply.github.com>
Date: Sat, 3 May 2025 17:15:59 +0200
Subject: [PATCH 1/3] libfuzzer: add standalone test for libfuzzer
 initialization

---
 test/standalone/build.zig.zon       |  3 +++
 test/standalone/libfuzzer/build.zig | 26 ++++++++++++++++++++++++++
 test/standalone/libfuzzer/main.zig  | 22 ++++++++++++++++++++++
 3 files changed, 51 insertions(+)
 create mode 100644 test/standalone/libfuzzer/build.zig
 create mode 100644 test/standalone/libfuzzer/main.zig

diff --git a/test/standalone/build.zig.zon b/test/standalone/build.zig.zon
index 44358b37f0..e1829b4878 100644
--- a/test/standalone/build.zig.zon
+++ b/test/standalone/build.zig.zon
@@ -108,6 +108,9 @@
         .libcxx = .{
             .path = "libcxx",
         },
+        .libfuzzer = .{
+            .path = "libfuzzer",
+        },
         .load_dynamic_library = .{
             .path = "load_dynamic_library",
         },
diff --git a/test/standalone/libfuzzer/build.zig b/test/standalone/libfuzzer/build.zig
new file mode 100644
index 0000000000..1260ce6e71
--- /dev/null
+++ b/test/standalone/libfuzzer/build.zig
@@ -0,0 +1,26 @@
+const std = @import("std");
+const builtin = @import("builtin");
+
+pub fn build(b: *std.Build) void {
+    const target = b.standardTargetOptions(.{});
+    const optimize = b.standardOptimizeOption(.{});
+
+    if (builtin.os.tag == .windows) return; // TODO: libfuzzer support for windows
+
+    const run_step = b.step("run", "Run executables");
+    const exe = b.addExecutable(.{
+        .name = "main",
+        .root_module = b.createModule(.{
+            .root_source_file = b.path("main.zig"),
+            .target = target,
+            .optimize = optimize,
+            .fuzz = true,
+        }),
+    });
+
+    b.installArtifact(exe);
+    b.default_step = run_step;
+
+    const run_artifact = b.addRunArtifact(exe);
+    run_step.dependOn(&run_artifact.step);
+}
diff --git a/test/standalone/libfuzzer/main.zig b/test/standalone/libfuzzer/main.zig
new file mode 100644
index 0000000000..b0a18c8b20
--- /dev/null
+++ b/test/standalone/libfuzzer/main.zig
@@ -0,0 +1,22 @@
+const std = @import("std");
+
+const FuzzerSlice = extern struct {
+    ptr: [*]const u8,
+    len: usize,
+
+    fn fromSlice(s: []const u8) FuzzerSlice {
+        return .{ .ptr = s.ptr, .len = s.len };
+    }
+};
+
+extern fn fuzzer_set_name(name_ptr: [*]const u8, name_len: usize) void;
+extern fn fuzzer_init(cache_dir: FuzzerSlice) void;
+extern fn fuzzer_init_corpus_elem(input_ptr: [*]const u8, input_len: usize) void;
+extern fn fuzzer_coverage_id() u64;
+
+pub fn main() !void {
+    fuzzer_init(FuzzerSlice.fromSlice(""));
+    fuzzer_init_corpus_elem("hello".ptr, "hello".len);
+    fuzzer_set_name("test".ptr, "test".len);
+    _ = fuzzer_coverage_id();
+}

From 68700e5de1e593d8f924e5ff0e7ebdd47373b3c8 Mon Sep 17 00:00:00 2001
From: tjog <28024277+tjog@users.noreply.github.com>
Date: Sat, 3 May 2025 17:17:07 +0200
Subject: [PATCH 2/3] link+macho+fuzz: use correct input type

A debug build of the compiler detects invalid union access since `classifyInputFile`
detects `.archive` and this line constructed a `.object` input.
---
 src/link/MachO.zig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/link/MachO.zig b/src/link/MachO.zig
index 2043be3e7b..f6ec0a74d8 100644
--- a/src/link/MachO.zig
+++ b/src/link/MachO.zig
@@ -416,7 +416,7 @@ pub fn flushModule(
     }
 
     if (comp.config.any_fuzz) {
-        try positionals.append(try link.openObjectInput(diags, comp.fuzzer_lib.?.full_object_path));
+        try positionals.append(try link.openArchiveInput(diags, comp.fuzzer_lib.?.full_object_path, false, false));
     }
 
     if (comp.ubsan_rt_lib) |crt_file| {

From 0ba77eca7430ecb7c9852df175f3fc175bf50bbf Mon Sep 17 00:00:00 2001
From: tjog <28024277+tjog@users.noreply.github.com>
Date: Sat, 3 May 2025 23:33:26 +0200
Subject: [PATCH 3/3] disable getauxvalImpl instrumentation as libfuzzer's
 allocator may need to call it

---
 lib/std/os/linux.zig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lib/std/os/linux.zig b/lib/std/os/linux.zig
index 794fccdf13..f055022203 100644
--- a/lib/std/os/linux.zig
+++ b/lib/std/os/linux.zig
@@ -523,6 +523,7 @@ pub const getauxval = if (extern_getauxval) struct {
 }.getauxval else getauxvalImpl;
 
 fn getauxvalImpl(index: usize) callconv(.c) usize {
+    @disableInstrumentation();
     const auxv = elf_aux_maybe orelse return 0;
     var i: usize = 0;
     while (auxv[i].a_type != std.elf.AT_NULL) : (i += 1) {