link-test: add test for entry in a dynamic library for MachO

test/link.zig

@@ -108,6 +108,10 @@ pub const cases = [_]Case{
         .build_root = "test/link/macho/entry_in_archive",
         .import = @import("link/macho/entry_in_archive/build.zig"),
     },
+    .{
+        .build_root = "test/link/macho/entry_in_dylib",
+        .import = @import("link/macho/entry_in_dylib/build.zig"),
+    },
     .{
         .build_root = "test/link/macho/headerpad",
         .import = @import("link/macho/headerpad/build.zig"),

test/link/macho/entry_in_dylib/bootstrap.c

@@ -0,0 +1,5 @@
+extern int my_main();
+
+int bootstrap() {
+  return my_main();
+}

test/link/macho/entry_in_dylib/build.zig

@@ -0,0 +1,53 @@
+const std = @import("std");
+
+pub const requires_symlinks = true;
+
+pub fn build(b: *std.Build) void {
+    const test_step = b.step("test", "Test it");
+    b.default_step = test_step;
+
+    add(b, test_step, .Debug);
+    add(b, test_step, .ReleaseFast);
+    add(b, test_step, .ReleaseSmall);
+    add(b, test_step, .ReleaseSafe);
+}
+
+fn add(b: *std.Build, test_step: *std.Build.Step, optimize: std.builtin.OptimizeMode) void {
+    const lib = b.addSharedLibrary(.{
+        .name = "bootstrap",
+        .optimize = optimize,
+        .target = .{ .os_tag = .macos },
+    });
+    lib.addCSourceFile("bootstrap.c", &.{});
+    lib.linkLibC();
+    lib.linker_allow_shlib_undefined = true;
+
+    const exe = b.addExecutable(.{
+        .name = "main",
+        .optimize = optimize,
+        .target = .{ .os_tag = .macos },
+    });
+    exe.addCSourceFile("main.c", &.{});
+    exe.linkLibrary(lib);
+    exe.linkLibC();
+    exe.entry_symbol_name = "_bootstrap";
+
+    const check_exe = exe.checkObject();
+    check_exe.checkStart("segname __TEXT");
+    check_exe.checkNext("vmaddr {text_vmaddr}");
+
+    check_exe.checkStart("sectname __stubs");
+    check_exe.checkNext("addr {stubs_vmaddr}");
+
+    check_exe.checkStart("cmd MAIN");
+    check_exe.checkNext("entryoff {entryoff}");
+
+    check_exe.checkComputeCompare("text_vmaddr entryoff +", .{
+        .op = .eq,
+        .value = .{ .variable = "stubs_vmaddr" }, // The entrypoint should be a synthetic stub
+    });
+
+    const run = check_exe.runAndCompare();
+    run.expectStdOutEqual("Hello!\n");
+    test_step.dependOn(&run.step);
+}

test/link/macho/entry_in_dylib/main.c

@@ -0,0 +1,6 @@
+#include <stdio.h>
+
+int my_main() {
+  fprintf(stdout, "Hello!\n");
+  return 0;
+}