Merge pull request #11910 from ziglang/linker-tests

build.zig

@@ -489,6 +489,7 @@ pub fn build(b: *Builder) !void {
 
     toolchain_step.dependOn(tests.addCompareOutputTests(b, test_filter, modes));
     toolchain_step.dependOn(tests.addStandaloneTests(b, test_filter, modes, skip_non_native, enable_macos_sdk, target));
+    toolchain_step.dependOn(tests.addLinkTests(b, test_filter, modes, enable_macos_sdk));
     toolchain_step.dependOn(tests.addStackTraceTests(b, test_filter, modes));
     toolchain_step.dependOn(tests.addCliTests(b, test_filter, modes));
     toolchain_step.dependOn(tests.addAssembleAndLinkTests(b, test_filter, modes));

ci/azure/macos_script

@@ -76,6 +76,7 @@ release/bin/zig build test-run-translated-c -Denable-macos-sdk
 release/bin/zig build docs                  -Denable-macos-sdk
 release/bin/zig build test-fmt              -Denable-macos-sdk
 release/bin/zig build test-cases            -Denable-macos-sdk -Dsingle-threaded
+release/bin/zig build test-link             -Denable-macos-sdk
 
 if [ "${BUILD_REASON}" != "PullRequest" ]; then
   mv ../LICENSE release/

lib/std/build.zig

@@ -24,6 +24,7 @@ pub const TranslateCStep = @import("build/TranslateCStep.zig");
 pub const WriteFileStep = @import("build/WriteFileStep.zig");
 pub const RunStep = @import("build/RunStep.zig");
 pub const CheckFileStep = @import("build/CheckFileStep.zig");
+pub const CheckObjectStep = @import("build/CheckObjectStep.zig");
 pub const InstallRawStep = @import("build/InstallRawStep.zig");
 pub const OptionsStep = @import("build/OptionsStep.zig");
 
@@ -1582,6 +1583,9 @@ pub const LibExeObjStep = struct {
     /// (Darwin) Path to entitlements file
     entitlements: ?[]const u8 = null,
 
+    /// (Darwin) Size of the pagezero segment.
+    pagezero_size: ?u64 = null,
+
     /// Position Independent Code
     force_pic: ?bool = null,
 
@@ -1861,6 +1865,10 @@ pub const LibExeObjStep = struct {
         return run_step;
     }
 
+    pub fn checkObject(self: *LibExeObjStep, obj_format: std.Target.ObjectFormat) *CheckObjectStep {
+        return CheckObjectStep.create(self.builder, self.getOutputSource(), obj_format);
+    }
+
     pub fn setLinkerScriptPath(self: *LibExeObjStep, source: FileSource) void {
         self.linker_script = source.dupe(self.builder);
         source.addStepDependencies(&self.step);
@@ -2638,6 +2646,10 @@ pub const LibExeObjStep = struct {
         if (self.entitlements) |entitlements| {
             try zig_args.appendSlice(&[_][]const u8{ "--entitlements", entitlements });
         }
+        if (self.pagezero_size) |pagezero_size| {
+            const size = try std.fmt.allocPrint(builder.allocator, "{x}", .{pagezero_size});
+            try zig_args.appendSlice(&[_][]const u8{ "-pagezero_size", size });
+        }
 
         if (self.bundle_compiler_rt) |x| {
             if (x) {
@@ -3443,6 +3455,7 @@ pub const Step = struct {
         write_file,
         run,
         check_file,
+        check_object,
         install_raw,
         options,
         custom,

lib/std/build/CheckObjectStep.zig

@@ -0,0 +1,392 @@
+const std = @import("../std.zig");
+const assert = std.debug.assert;
+const build = std.build;
+const fs = std.fs;
+const macho = std.macho;
+const mem = std.mem;
+const testing = std.testing;
+
+const CheckObjectStep = @This();
+
+const Allocator = mem.Allocator;
+const Builder = build.Builder;
+const Step = build.Step;
+
+pub const base_id = .check_obj;
+
+step: Step,
+builder: *Builder,
+source: build.FileSource,
+max_bytes: usize = 20 * 1024 * 1024,
+checks: std.ArrayList(Check),
+dump_symtab: bool = false,
+obj_format: std.Target.ObjectFormat,
+
+pub fn create(builder: *Builder, source: build.FileSource, obj_format: std.Target.ObjectFormat) *CheckObjectStep {
+    const gpa = builder.allocator;
+    const self = gpa.create(CheckObjectStep) catch unreachable;
+    self.* = .{
+        .builder = builder,
+        .step = Step.init(.check_file, "CheckObject", gpa, make),
+        .source = source.dupe(builder),
+        .checks = std.ArrayList(Check).init(gpa),
+        .obj_format = obj_format,
+    };
+    self.source.addStepDependencies(&self.step);
+    return self;
+}
+
+const Action = union(enum) {
+    match: MatchAction,
+    compute_eq: ComputeEqAction,
+};
+
+/// MatchAction is the main building block of standard matchers with optional eat-all token `{*}`
+/// and extractors by name such as `{n_value}`. Please note this action is very simplistic in nature
+/// i.e., it won't really handle edge cases/nontrivial examples. But given that we do want to use
+/// it mainly to test the output of our object format parser-dumpers when testing the linkers, etc.
+/// it should be plenty useful in its current form.
+const MatchAction = struct {
+    needle: []const u8,
+
+    /// Will return true if the `needle` was found in the `haystack`.
+    /// Some examples include:
+    ///
+    /// LC 0                     => will match in its entirety
+    /// vmaddr {vmaddr}          => will match `vmaddr` and then extract the following value as u64
+    ///                             and save under `vmaddr` global name (see `global_vars` param)
+    /// name {*}libobjc{*}.dylib => will match `name` followed by a token which contains `libobjc` and `.dylib`
+    ///                             in that order with other letters in between
+    fn match(act: MatchAction, haystack: []const u8, global_vars: anytype) !bool {
+        var hay_it = mem.tokenize(u8, mem.trim(u8, haystack, " "), " ");
+        var needle_it = mem.tokenize(u8, mem.trim(u8, act.needle, " "), " ");
+
+        while (needle_it.next()) |needle_tok| {
+            const hay_tok = hay_it.next() orelse return false;
+
+            if (mem.indexOf(u8, needle_tok, "{*}")) |index| {
+                // We have fuzzy matchers within the search pattern, so we match substrings.
+                var start = index;
+                var n_tok = needle_tok;
+                var h_tok = hay_tok;
+                while (true) {
+                    n_tok = n_tok[start + 3 ..];
+                    const inner = if (mem.indexOf(u8, n_tok, "{*}")) |sub_end|
+                        n_tok[0..sub_end]
+                    else
+                        n_tok;
+                    if (mem.indexOf(u8, h_tok, inner) == null) return false;
+                    start = mem.indexOf(u8, n_tok, "{*}") orelse break;
+                }
+            } else if (mem.startsWith(u8, needle_tok, "{")) {
+                const closing_brace = mem.indexOf(u8, needle_tok, "}") orelse return error.MissingClosingBrace;
+                if (closing_brace != needle_tok.len - 1) return error.ClosingBraceNotLast;
+
+                const name = needle_tok[1..closing_brace];
+                if (name.len == 0) return error.MissingBraceValue;
+                const value = try std.fmt.parseInt(u64, hay_tok, 16);
+                try global_vars.putNoClobber(name, value);
+            } else {
+                if (!mem.eql(u8, hay_tok, needle_tok)) return false;
+            }
+        }
+
+        return true;
+    }
+};
+
+/// ComputeEqAction can be used to perform an operation on the extracted global variables
+/// using the MatchAction. It currently only supports an addition. The operation is required
+/// to be specified in Reverse Polish Notation to ease in operator-precedence parsing (well,
+/// to avoid any parsing really).
+/// For example, if the two extracted values were saved as `vmaddr` and `entryoff` respectively
+/// they could then be added with this simple program `vmaddr entryoff +`.
+const ComputeEqAction = struct {
+    expected: []const u8,
+    var_stack: std.ArrayList([]const u8),
+    op_stack: std.ArrayList(Op),
+
+    const Op = enum {
+        add,
+    };
+};
+
+const Check = struct {
+    builder: *Builder,
+    actions: std.ArrayList(Action),
+
+    fn create(b: *Builder) Check {
+        return .{
+            .builder = b,
+            .actions = std.ArrayList(Action).init(b.allocator),
+        };
+    }
+
+    fn match(self: *Check, needle: []const u8) void {
+        self.actions.append(.{
+            .match = .{ .needle = self.builder.dupe(needle) },
+        }) catch unreachable;
+    }
+
+    fn computeEq(self: *Check, act: ComputeEqAction) void {
+        self.actions.append(.{
+            .compute_eq = act,
+        }) catch unreachable;
+    }
+};
+
+/// Creates a new sequence of actions with `phrase` as the first anchor searched phrase.
+pub fn checkStart(self: *CheckObjectStep, phrase: []const u8) void {
+    var new_check = Check.create(self.builder);
+    new_check.match(phrase);
+    self.checks.append(new_check) catch unreachable;
+}
+
+/// Adds another searched phrase to the latest created Check with `CheckObjectStep.checkStart(...)`.
+/// Asserts at least one check already exists.
+pub fn checkNext(self: *CheckObjectStep, phrase: []const u8) void {
+    assert(self.checks.items.len > 0);
+    const last = &self.checks.items[self.checks.items.len - 1];
+    last.match(phrase);
+}
+
+/// Creates a new check checking specifically symbol table parsed and dumped from the object
+/// file.
+/// Issuing this check will force parsing and dumping of the symbol table.
+pub fn checkInSymtab(self: *CheckObjectStep) void {
+    self.dump_symtab = true;
+    const symtab_label = switch (self.obj_format) {
+        .macho => MachODumper.symtab_label,
+        else => @panic("TODO other parsers"),
+    };
+    self.checkStart(symtab_label);
+}
+
+/// Creates a new standalone, singular check which allows running simple binary operations
+/// on the extracted variables. It will then compare the reduced program with the value of
+/// the expected variable.
+pub fn checkComputeEq(self: *CheckObjectStep, program: []const u8, expected: []const u8) void {
+    const gpa = self.builder.allocator;
+    var ca = ComputeEqAction{
+        .expected = expected,
+        .var_stack = std.ArrayList([]const u8).init(gpa),
+        .op_stack = std.ArrayList(ComputeEqAction.Op).init(gpa),
+    };
+
+    var it = mem.tokenize(u8, program, " ");
+    while (it.next()) |next| {
+        if (mem.eql(u8, next, "+")) {
+            ca.op_stack.append(.add) catch unreachable;
+        } else {
+            ca.var_stack.append(self.builder.dupe(next)) catch unreachable;
+        }
+    }
+
+    var new_check = Check.create(self.builder);
+    new_check.computeEq(ca);
+    self.checks.append(new_check) catch unreachable;
+}
+
+fn make(step: *Step) !void {
+    const self = @fieldParentPtr(CheckObjectStep, "step", step);
+
+    const gpa = self.builder.allocator;
+    const src_path = self.source.getPath(self.builder);
+    const contents = try fs.cwd().readFileAlloc(gpa, src_path, self.max_bytes);
+
+    const output = switch (self.obj_format) {
+        .macho => try MachODumper.parseAndDump(contents, .{
+            .gpa = gpa,
+            .dump_symtab = self.dump_symtab,
+        }),
+        .elf => @panic("TODO elf parser"),
+        .coff => @panic("TODO coff parser"),
+        .wasm => @panic("TODO wasm parser"),
+        else => unreachable,
+    };
+
+    var vars = std.StringHashMap(u64).init(gpa);
+
+    for (self.checks.items) |chk| {
+        var it = mem.tokenize(u8, output, "\r\n");
+        for (chk.actions.items) |act| {
+            switch (act) {
+                .match => |match_act| {
+                    while (it.next()) |line| {
+                        if (try match_act.match(line, &vars)) break;
+                    } else {
+                        std.debug.print(
+                            \\
+                            \\========= Expected to find: ==========================
+                            \\{s}
+                            \\========= But parsed file does not contain it: =======
+                            \\{s}
+                            \\
+                        , .{ match_act.needle, output });
+                        return error.TestFailed;
+                    }
+                },
+                .compute_eq => |c_eq| {
+                    var values = std.ArrayList(u64).init(gpa);
+                    try values.ensureTotalCapacity(c_eq.var_stack.items.len);
+                    for (c_eq.var_stack.items) |vv| {
+                        const val = vars.get(vv) orelse {
+                            std.debug.print(
+                                \\
+                                \\========= Variable was not extracted: ===========
+                                \\{s}
+                                \\========= From parsed file: =====================
+                                \\{s}
+                                \\
+                            , .{ vv, output });
+                            return error.TestFailed;
+                        };
+                        values.appendAssumeCapacity(val);
+                    }
+
+                    var op_i: usize = 1;
+                    var reduced: u64 = values.items[0];
+                    for (c_eq.op_stack.items) |op| {
+                        const other = values.items[op_i];
+                        switch (op) {
+                            .add => {
+                                reduced += other;
+                            },
+                        }
+                    }
+
+                    const expected = vars.get(c_eq.expected) orelse {
+                        std.debug.print(
+                            \\
+                            \\========= Variable was not extracted: ===========
+                            \\{s}
+                            \\========= From parsed file: =====================
+                            \\{s}
+                            \\
+                        , .{ c_eq.expected, output });
+                        return error.TestFailed;
+                    };
+                    try testing.expectEqual(reduced, expected);
+                },
+            }
+        }
+    }
+}
+
+const Opts = struct {
+    gpa: ?Allocator = null,
+    dump_symtab: bool = false,
+};
+
+const MachODumper = struct {
+    const symtab_label = "symtab";
+
+    fn parseAndDump(bytes: []const u8, opts: Opts) ![]const u8 {
+        const gpa = opts.gpa orelse unreachable; // MachO dumper requires an allocator
+        var stream = std.io.fixedBufferStream(bytes);
+        const reader = stream.reader();
+
+        const hdr = try reader.readStruct(macho.mach_header_64);
+        if (hdr.magic != macho.MH_MAGIC_64) {
+            return error.InvalidMagicNumber;
+        }
+
+        var output = std.ArrayList(u8).init(gpa);
+        const writer = output.writer();
+
+        var symtab_cmd: ?macho.symtab_command = null;
+        var i: u16 = 0;
+        while (i < hdr.ncmds) : (i += 1) {
+            var cmd = try macho.LoadCommand.read(gpa, reader);
+
+            if (opts.dump_symtab and cmd.cmd() == .SYMTAB) {
+                symtab_cmd = cmd.symtab;
+            }
+
+            try dumpLoadCommand(cmd, i, writer);
+            try writer.writeByte('\n');
+        }
+
+        if (symtab_cmd) |cmd| {
+            try writer.writeAll(symtab_label ++ "\n");
+            const strtab = bytes[cmd.stroff..][0..cmd.strsize];
+            const raw_symtab = bytes[cmd.symoff..][0 .. cmd.nsyms * @sizeOf(macho.nlist_64)];
+            const symtab = mem.bytesAsSlice(macho.nlist_64, raw_symtab);
+
+            for (symtab) |sym| {
+                if (sym.stab()) continue;
+                const sym_name = mem.sliceTo(@ptrCast([*:0]const u8, strtab.ptr + sym.n_strx), 0);
+                try writer.print("{s} {x}\n", .{ sym_name, sym.n_value });
+            }
+        }
+
+        return output.toOwnedSlice();
+    }
+
+    fn dumpLoadCommand(lc: macho.LoadCommand, index: u16, writer: anytype) !void {
+        // print header first
+        try writer.print(
+            \\LC {d}
+            \\cmd {s}
+            \\cmdsize {d}
+        , .{ index, @tagName(lc.cmd()), lc.cmdsize() });
+
+        switch (lc.cmd()) {
+            .SEGMENT_64 => {
+                // TODO dump section headers
+                const seg = lc.segment.inner;
+                try writer.writeByte('\n');
+                try writer.print(
+                    \\segname {s}
+                    \\vmaddr {x}
+                    \\vmsize {x}
+                    \\fileoff {x}
+                    \\filesz {x}
+                , .{
+                    seg.segName(),
+                    seg.vmaddr,
+                    seg.vmsize,
+                    seg.fileoff,
+                    seg.filesize,
+                });
+            },
+
+            .ID_DYLIB,
+            .LOAD_DYLIB,
+            => {
+                const dylib = lc.dylib.inner.dylib;
+                try writer.writeByte('\n');
+                try writer.print(
+                    \\name {s}
+                    \\timestamp {d}
+                    \\current version {x}
+                    \\compatibility version {x}
+                , .{
+                    mem.sliceTo(lc.dylib.data, 0),
+                    dylib.timestamp,
+                    dylib.current_version,
+                    dylib.compatibility_version,
+                });
+            },
+
+            .MAIN => {
+                try writer.writeByte('\n');
+                try writer.print(
+                    \\entryoff {x}
+                    \\stacksize {x}
+                , .{ lc.main.entryoff, lc.main.stacksize });
+            },
+
+            .RPATH => {
+                try writer.writeByte('\n');
+                try writer.print(
+                    \\path {s}
+                , .{
+                    mem.sliceTo(lc.rpath.data, 0),
+                });
+            },
+
+            else => {},
+        }
+    }
+};

lib/std/build/RunStep.zig

@@ -149,6 +149,7 @@ fn make(step: *Step) !void {
     const cwd = if (self.cwd) |cwd| self.builder.pathFromRoot(cwd) else self.builder.build_root;
 
     var argv_list = ArrayList([]const u8).init(self.builder.allocator);
+
     for (self.argv.items) |arg| {
         switch (arg) {
             .bytes => |bytes| try argv_list.append(bytes),

src/link/MachO.zig

@@ -934,6 +934,11 @@ pub fn flushModule(self: *MachO, comp: *Compilation, prog_node: *std.Progress.No
                     try argv.append(try std.fmt.allocPrint(arena, "0x{x}", .{pagezero_size}));
                 }
 
+                if (self.base.options.entry) |entry| {
+                    try argv.append("-e");
+                    try argv.append(entry);
+                }
+
                 try argv.appendSlice(positionals.items);
 
                 try argv.append("-o");
@@ -3371,13 +3376,12 @@ fn addCodeSignatureLC(self: *MachO) !void {
 fn setEntryPoint(self: *MachO) !void {
     if (self.base.options.output_mode != .Exe) return;
 
-    // TODO we should respect the -entry flag passed in by the user to set a custom
-    // entrypoint. For now, assume default of `_main`.
     const seg = self.load_commands.items[self.text_segment_cmd_index.?].segment;
-    const n_strx = self.strtab_dir.getKeyAdapted(@as([]const u8, "_main"), StringIndexAdapter{
+    const entry_name = self.base.options.entry orelse "_main";
+    const n_strx = self.strtab_dir.getKeyAdapted(entry_name, StringIndexAdapter{
         .bytes = &self.strtab,
     }) orelse {
-        log.err("'_main' export not found", .{});
+        log.err("entrypoint '{s}' not found", .{entry_name});
         return error.MissingMainEntrypoint;
     };
     const resolv = self.symbol_resolver.get(n_strx) orelse unreachable;
@@ -5711,28 +5715,46 @@ fn writeDyldInfoData(self: *MachO) !void {
 
     const seg = &self.load_commands.items[self.linkedit_segment_cmd_index.?].segment;
     const dyld_info = &self.load_commands.items[self.dyld_info_cmd_index.?].dyld_info_only;
+
+    const rebase_off = mem.alignForwardGeneric(u64, seg.inner.fileoff, @alignOf(u64));
     const rebase_size = try bind.rebaseInfoSize(rebase_pointers.items);
+    dyld_info.rebase_off = @intCast(u32, rebase_off);
+    dyld_info.rebase_size = @intCast(u32, rebase_size);
+    log.debug("writing rebase info from 0x{x} to 0x{x}", .{
+        dyld_info.rebase_off,
+        dyld_info.rebase_off + dyld_info.rebase_size,
+    });
+
+    const bind_off = mem.alignForwardGeneric(u64, dyld_info.rebase_off + dyld_info.rebase_size, @alignOf(u64));
     const bind_size = try bind.bindInfoSize(bind_pointers.items);
+    dyld_info.bind_off = @intCast(u32, bind_off);
+    dyld_info.bind_size = @intCast(u32, bind_size);
+    log.debug("writing bind info from 0x{x} to 0x{x}", .{
+        dyld_info.bind_off,
+        dyld_info.bind_off + dyld_info.bind_size,
+    });
+
+    const lazy_bind_off = mem.alignForwardGeneric(u64, dyld_info.bind_off + dyld_info.bind_size, @alignOf(u64));
     const lazy_bind_size = try bind.lazyBindInfoSize(lazy_bind_pointers.items);
+    dyld_info.lazy_bind_off = @intCast(u32, lazy_bind_off);
+    dyld_info.lazy_bind_size = @intCast(u32, lazy_bind_size);
+    log.debug("writing lazy bind info from 0x{x} to 0x{x}", .{
+        dyld_info.lazy_bind_off,
+        dyld_info.lazy_bind_off + dyld_info.lazy_bind_size,
+    });
+
+    const export_off = mem.alignForwardGeneric(u64, dyld_info.lazy_bind_off + dyld_info.lazy_bind_size, @alignOf(u64));
     const export_size = trie.size;
+    dyld_info.export_off = @intCast(u32, export_off);
+    dyld_info.export_size = @intCast(u32, export_size);
+    log.debug("writing export trie from 0x{x} to 0x{x}", .{
+        dyld_info.export_off,
+        dyld_info.export_off + dyld_info.export_size,
+    });
 
-    dyld_info.rebase_off = @intCast(u32, seg.inner.fileoff);
-    dyld_info.rebase_size = @intCast(u32, mem.alignForwardGeneric(u64, rebase_size, @alignOf(u64)));
-    seg.inner.filesize += dyld_info.rebase_size;
+    seg.inner.filesize = dyld_info.export_off + dyld_info.export_size - seg.inner.fileoff;
 
-    dyld_info.bind_off = dyld_info.rebase_off + dyld_info.rebase_size;
-    dyld_info.bind_size = @intCast(u32, mem.alignForwardGeneric(u64, bind_size, @alignOf(u64)));
-    seg.inner.filesize += dyld_info.bind_size;
-
-    dyld_info.lazy_bind_off = dyld_info.bind_off + dyld_info.bind_size;
-    dyld_info.lazy_bind_size = @intCast(u32, mem.alignForwardGeneric(u64, lazy_bind_size, @alignOf(u64)));
-    seg.inner.filesize += dyld_info.lazy_bind_size;
-
-    dyld_info.export_off = dyld_info.lazy_bind_off + dyld_info.lazy_bind_size;
-    dyld_info.export_size = @intCast(u32, mem.alignForwardGeneric(u64, export_size, @alignOf(u64)));
-    seg.inner.filesize += dyld_info.export_size;
-
-    const needed_size = dyld_info.rebase_size + dyld_info.bind_size + dyld_info.lazy_bind_size + dyld_info.export_size;
+    const needed_size = dyld_info.export_off + dyld_info.export_size - dyld_info.rebase_off;
     var buffer = try self.base.allocator.alloc(u8, needed_size);
     defer self.base.allocator.free(buffer);
     mem.set(u8, buffer, 0);
@@ -5740,14 +5762,15 @@ fn writeDyldInfoData(self: *MachO) !void {
     var stream = std.io.fixedBufferStream(buffer);
     const writer = stream.writer();
 
+    const base_off = dyld_info.rebase_off;
     try bind.writeRebaseInfo(rebase_pointers.items, writer);
-    try stream.seekBy(@intCast(i64, dyld_info.rebase_size) - @intCast(i64, rebase_size));
+    try stream.seekTo(dyld_info.bind_off - base_off);
 
     try bind.writeBindInfo(bind_pointers.items, writer);
-    try stream.seekBy(@intCast(i64, dyld_info.bind_size) - @intCast(i64, bind_size));
+    try stream.seekTo(dyld_info.lazy_bind_off - base_off);
 
     try bind.writeLazyBindInfo(lazy_bind_pointers.items, writer);
-    try stream.seekBy(@intCast(i64, dyld_info.lazy_bind_size) - @intCast(i64, lazy_bind_size));
+    try stream.seekTo(dyld_info.export_off - base_off);
 
     _ = try trie.write(writer);
 
@@ -5758,7 +5781,7 @@ fn writeDyldInfoData(self: *MachO) !void {
 
     try self.base.file.?.pwriteAll(buffer, dyld_info.rebase_off);
     try self.populateLazyBindOffsetsInStubHelper(
-        buffer[dyld_info.rebase_size + dyld_info.bind_size ..][0..dyld_info.lazy_bind_size],
+        buffer[dyld_info.lazy_bind_off - base_off ..][0..dyld_info.lazy_bind_size],
     );
     self.load_commands_dirty = true;
 }
@@ -5928,32 +5951,31 @@ fn writeFunctionStarts(self: *MachO) !void {
         } else break;
     }
 
-    const max_size = @intCast(usize, offsets.items.len * @sizeOf(u64));
-    var buffer = try self.base.allocator.alloc(u8, max_size);
-    defer self.base.allocator.free(buffer);
-    mem.set(u8, buffer, 0);
+    var buffer = std.ArrayList(u8).init(self.base.allocator);
+    defer buffer.deinit();
 
-    var stream = std.io.fixedBufferStream(buffer);
-    const writer = stream.writer();
+    const max_size = @intCast(usize, offsets.items.len * @sizeOf(u64));
+    try buffer.ensureTotalCapacity(max_size);
 
     for (offsets.items) |offset| {
-        try std.leb.writeULEB128(writer, offset);
+        try std.leb.writeULEB128(buffer.writer(), offset);
     }
 
-    const needed_size = @intCast(u32, mem.alignForwardGeneric(u64, stream.pos, @sizeOf(u64)));
     const seg = &self.load_commands.items[self.linkedit_segment_cmd_index.?].segment;
     const fn_cmd = &self.load_commands.items[self.function_starts_cmd_index.?].linkedit_data;
 
-    fn_cmd.dataoff = @intCast(u32, seg.inner.fileoff + seg.inner.filesize);
-    fn_cmd.datasize = needed_size;
-    seg.inner.filesize += needed_size;
+    const dataoff = mem.alignForwardGeneric(u64, seg.inner.fileoff + seg.inner.filesize, @alignOf(u64));
+    const datasize = buffer.items.len;
+    fn_cmd.dataoff = @intCast(u32, dataoff);
+    fn_cmd.datasize = @intCast(u32, datasize);
+    seg.inner.filesize = fn_cmd.dataoff + fn_cmd.datasize - seg.inner.fileoff;
 
     log.debug("writing function starts info from 0x{x} to 0x{x}", .{
         fn_cmd.dataoff,
         fn_cmd.dataoff + fn_cmd.datasize,
     });
 
-    try self.base.file.?.pwriteAll(buffer[0..needed_size], fn_cmd.dataoff);
+    try self.base.file.?.pwriteAll(buffer.items, fn_cmd.dataoff);
     self.load_commands_dirty = true;
 }
 
@@ -6001,11 +6023,12 @@ fn writeDices(self: *MachO) !void {
 
     const seg = &self.load_commands.items[self.linkedit_segment_cmd_index.?].segment;
     const dice_cmd = &self.load_commands.items[self.data_in_code_cmd_index.?].linkedit_data;
-    const needed_size = @intCast(u32, buf.items.len);
 
-    dice_cmd.dataoff = @intCast(u32, seg.inner.fileoff + seg.inner.filesize);
-    dice_cmd.datasize = needed_size;
-    seg.inner.filesize += needed_size;
+    const dataoff = mem.alignForwardGeneric(u64, seg.inner.fileoff + seg.inner.filesize, @alignOf(u64));
+    const datasize = buf.items.len;
+    dice_cmd.dataoff = @intCast(u32, dataoff);
+    dice_cmd.datasize = @intCast(u32, datasize);
+    seg.inner.filesize = dice_cmd.dataoff + dice_cmd.datasize - seg.inner.fileoff;
 
     log.debug("writing data-in-code from 0x{x} to 0x{x}", .{
         dice_cmd.dataoff,
@@ -6022,7 +6045,8 @@ fn writeSymbolTable(self: *MachO) !void {
 
     const seg = &self.load_commands.items[self.linkedit_segment_cmd_index.?].segment;
     const symtab = &self.load_commands.items[self.symtab_cmd_index.?].symtab;
-    symtab.symoff = @intCast(u32, seg.inner.fileoff + seg.inner.filesize);
+    const symoff = mem.alignForwardGeneric(u64, seg.inner.fileoff + seg.inner.filesize, @alignOf(macho.nlist_64));
+    symtab.symoff = @intCast(u32, symoff);
 
     var locals = std.ArrayList(macho.nlist_64).init(self.base.allocator);
     defer locals.deinit();
@@ -6122,7 +6146,7 @@ fn writeSymbolTable(self: *MachO) !void {
     try self.base.file.?.pwriteAll(mem.sliceAsBytes(undefs.items), undefs_off);
 
     symtab.nsyms = @intCast(u32, nlocals + nexports + nundefs);
-    seg.inner.filesize += locals_size + exports_size + undefs_size;
+    seg.inner.filesize = symtab.symoff + symtab.nsyms * @sizeOf(macho.nlist_64) - seg.inner.fileoff;
 
     // Update dynamic symbol table.
     const dysymtab = &self.load_commands.items[self.dysymtab_cmd_index.?].dysymtab;
@@ -6142,22 +6166,21 @@ fn writeSymbolTable(self: *MachO) !void {
     const nstubs = @intCast(u32, self.stubs_table.keys().len);
     const ngot_entries = @intCast(u32, self.got_entries_table.keys().len);
 
-    dysymtab.indirectsymoff = @intCast(u32, seg.inner.fileoff + seg.inner.filesize);
+    const indirectsymoff = mem.alignForwardGeneric(u64, seg.inner.fileoff + seg.inner.filesize, @alignOf(u64));
+    dysymtab.indirectsymoff = @intCast(u32, indirectsymoff);
     dysymtab.nindirectsyms = nstubs * 2 + ngot_entries;
 
-    const needed_size = dysymtab.nindirectsyms * @sizeOf(u32);
-    seg.inner.filesize += needed_size;
+    seg.inner.filesize = dysymtab.indirectsymoff + dysymtab.nindirectsyms * @sizeOf(u32) - seg.inner.fileoff;
 
     log.debug("writing indirect symbol table from 0x{x} to 0x{x}", .{
         dysymtab.indirectsymoff,
-        dysymtab.indirectsymoff + needed_size,
+        dysymtab.indirectsymoff + dysymtab.nindirectsyms * @sizeOf(u32),
     });
 
-    var buf = try self.base.allocator.alloc(u8, needed_size);
-    defer self.base.allocator.free(buf);
-
-    var stream = std.io.fixedBufferStream(buf);
-    var writer = stream.writer();
+    var buf = std.ArrayList(u8).init(self.base.allocator);
+    defer buf.deinit();
+    try buf.ensureTotalCapacity(dysymtab.nindirectsyms * @sizeOf(u32));
+    const writer = buf.writer();
 
     stubs.reserved1 = 0;
     for (self.stubs_table.keys()) |key| {
@@ -6191,7 +6214,9 @@ fn writeSymbolTable(self: *MachO) !void {
         }
     }
 
-    try self.base.file.?.pwriteAll(buf, dysymtab.indirectsymoff);
+    assert(buf.items.len == dysymtab.nindirectsyms * @sizeOf(u32));
+
+    try self.base.file.?.pwriteAll(buf.items, dysymtab.indirectsymoff);
     self.load_commands_dirty = true;
 }
 
@@ -6201,18 +6226,16 @@ fn writeStringTable(self: *MachO) !void {
 
     const seg = &self.load_commands.items[self.linkedit_segment_cmd_index.?].segment;
     const symtab = &self.load_commands.items[self.symtab_cmd_index.?].symtab;
-    symtab.stroff = @intCast(u32, seg.inner.fileoff + seg.inner.filesize);
-    symtab.strsize = @intCast(u32, mem.alignForwardGeneric(u64, self.strtab.items.len, @alignOf(u64)));
-    seg.inner.filesize += symtab.strsize;
+    const stroff = mem.alignForwardGeneric(u64, seg.inner.fileoff + seg.inner.filesize, @alignOf(u64));
+    const strsize = self.strtab.items.len;
+    symtab.stroff = @intCast(u32, stroff);
+    symtab.strsize = @intCast(u32, strsize);
+    seg.inner.filesize = symtab.stroff + symtab.strsize - seg.inner.fileoff;
 
     log.debug("writing string table from 0x{x} to 0x{x}", .{ symtab.stroff, symtab.stroff + symtab.strsize });
 
     try self.base.file.?.pwriteAll(self.strtab.items, symtab.stroff);
 
-    if (symtab.strsize > self.strtab.items.len) {
-        // This is potentially the last section, so we need to pad it out.
-        try self.base.file.?.pwriteAll(&[_]u8{0}, seg.inner.fileoff + seg.inner.filesize - 1);
-    }
     self.load_commands_dirty = true;
 }
 
@@ -6236,25 +6259,22 @@ fn writeCodeSignaturePadding(self: *MachO, code_sig: *CodeSignature) !void {
     const tracy = trace(@src());
     defer tracy.end();
 
-    const linkedit_segment = &self.load_commands.items[self.linkedit_segment_cmd_index.?].segment;
-    const code_sig_cmd = &self.load_commands.items[self.code_signature_cmd_index.?].linkedit_data;
+    const seg = &self.load_commands.items[self.linkedit_segment_cmd_index.?].segment;
+    const cs_cmd = &self.load_commands.items[self.code_signature_cmd_index.?].linkedit_data;
     // Code signature data has to be 16-bytes aligned for Apple tools to recognize the file
     // https://github.com/opensource-apple/cctools/blob/fdb4825f303fd5c0751be524babd32958181b3ed/libstuff/checkout.c#L271
-    const fileoff = mem.alignForwardGeneric(u64, linkedit_segment.inner.fileoff + linkedit_segment.inner.filesize, 16);
-    const padding = fileoff - (linkedit_segment.inner.fileoff + linkedit_segment.inner.filesize);
-    const needed_size = code_sig.estimateSize(fileoff);
-    code_sig_cmd.dataoff = @intCast(u32, fileoff);
-    code_sig_cmd.datasize = needed_size;
+    const dataoff = mem.alignForwardGeneric(u64, seg.inner.fileoff + seg.inner.filesize, 16);
+    const datasize = code_sig.estimateSize(dataoff);
+    cs_cmd.dataoff = @intCast(u32, dataoff);
+    cs_cmd.datasize = @intCast(u32, code_sig.estimateSize(dataoff));
 
     // Advance size of __LINKEDIT segment
-    linkedit_segment.inner.filesize += needed_size + padding;
-    if (linkedit_segment.inner.vmsize < linkedit_segment.inner.filesize) {
-        linkedit_segment.inner.vmsize = mem.alignForwardGeneric(u64, linkedit_segment.inner.filesize, self.page_size);
-    }
-    log.debug("writing code signature padding from 0x{x} to 0x{x}", .{ fileoff, fileoff + needed_size });
+    seg.inner.filesize = cs_cmd.dataoff + cs_cmd.datasize - seg.inner.fileoff;
+    seg.inner.vmsize = mem.alignForwardGeneric(u64, seg.inner.filesize, self.page_size);
+    log.debug("writing code signature padding from 0x{x} to 0x{x}", .{ dataoff, dataoff + datasize });
     // Pad out the space. We need to do this to calculate valid hashes for everything in the file
     // except for code signature data.
-    try self.base.file.?.pwriteAll(&[_]u8{0}, fileoff + needed_size - 1);
+    try self.base.file.?.pwriteAll(&[_]u8{0}, dataoff + datasize - 1);
     self.load_commands_dirty = true;
 }
 

test/link.zig

@@ -0,0 +1,64 @@
+const std = @import("std");
+const builtin = @import("builtin");
+const tests = @import("tests.zig");
+
+pub fn addCases(cases: *tests.StandaloneContext) void {
+    cases.addBuildFile("test/link/bss/build.zig", .{
+        .build_modes = false, // we only guarantee zerofill for undefined in Debug
+    });
+
+    cases.addBuildFile("test/link/common_symbols/build.zig", .{
+        .build_modes = true,
+    });
+
+    cases.addBuildFile("test/link/common_symbols_alignment/build.zig", .{
+        .build_modes = true,
+    });
+
+    cases.addBuildFile("test/link/interdependent_static_c_libs/build.zig", .{
+        .build_modes = true,
+    });
+
+    cases.addBuildFile("test/link/static_lib_as_system_lib/build.zig", .{
+        .build_modes = true,
+    });
+
+    cases.addBuildFile("test/link/tls/build.zig", .{
+        .build_modes = true,
+    });
+
+    if (builtin.os.tag == .macos) {
+        cases.addBuildFile("test/link/macho/entry/build.zig", .{
+            .build_modes = true,
+        });
+
+        cases.addBuildFile("test/link/macho/pagezero/build.zig", .{
+            .build_modes = false,
+        });
+
+        cases.addBuildFile("test/link/macho/dylib/build.zig", .{
+            .build_modes = true,
+        });
+
+        cases.addBuildFile("test/link/macho/frameworks/build.zig", .{
+            .build_modes = true,
+            .requires_macos_sdk = true,
+        });
+
+        // Try to build and run an Objective-C executable.
+        cases.addBuildFile("test/link/macho/objc/build.zig", .{
+            .build_modes = true,
+            .requires_macos_sdk = true,
+        });
+
+        // Try to build and run an Objective-C++ executable.
+        cases.addBuildFile("test/link/macho/objcpp/build.zig", .{
+            .build_modes = true,
+            .requires_macos_sdk = true,
+        });
+
+        cases.addBuildFile("test/link/macho/stack_size/build.zig", .{
+            .build_modes = true,
+        });
+    }
+}

test/link/bss/build.zig

@@ -0,0 +1,14 @@
+const Builder = @import("std").build.Builder;
+
+pub fn build(b: *Builder) void {
+    const mode = b.standardReleaseOptions();
+    const test_step = b.step("test", "Test");
+
+    const exe = b.addExecutable("bss", "main.zig");
+    b.default_step.dependOn(&exe.step);
+    exe.setBuildMode(mode);
+
+    const run = exe.run();
+    run.expectStdOutEqual("0, 1, 0\n");
+    test_step.dependOn(&run.step);
+}

test/link/bss/main.zig

@@ -0,0 +1,13 @@
+const std = @import("std");
+
+// Stress test zerofill layout
+var buffer: [0x1000000]u64 = undefined;
+
+pub fn main() anyerror!void {
+    buffer[0x10] = 1;
+    try std.io.getStdOut().writer().print("{d}, {d}, {d}\n", .{
+        buffer[0],
+        buffer[0x10],
+        buffer[0x1000000 - 1],
+    });
+}

test/link/macho/dylib/a.c

@@ -0,0 +1,7 @@
+#include <stdio.h>
+
+char world[] = "world";
+
+char* hello() {
+  return "Hello";
+}

test/link/macho/dylib/build.zig

@@ -0,0 +1,49 @@
+const std = @import("std");
+const Builder = std.build.Builder;
+
+pub fn build(b: *Builder) void {
+    const mode = b.standardReleaseOptions();
+
+    const test_step = b.step("test", "Test");
+    test_step.dependOn(b.getInstallStep());
+
+    const dylib = b.addSharedLibrary("a", null, b.version(1, 0, 0));
+    dylib.setBuildMode(mode);
+    dylib.addCSourceFile("a.c", &.{});
+    dylib.linkLibC();
+    dylib.install();
+
+    const check_dylib = dylib.checkObject(.macho);
+    check_dylib.checkStart("cmd ID_DYLIB");
+    check_dylib.checkNext("name @rpath/liba.dylib");
+    check_dylib.checkNext("timestamp 2");
+    check_dylib.checkNext("current version 10000");
+    check_dylib.checkNext("compatibility version 10000");
+
+    test_step.dependOn(&check_dylib.step);
+
+    const exe = b.addExecutable("main", null);
+    exe.setBuildMode(mode);
+    exe.addCSourceFile("main.c", &.{});
+    exe.linkSystemLibrary("a");
+    exe.linkLibC();
+    exe.addLibraryPath(b.pathFromRoot("zig-out/lib/"));
+    exe.addRPath(b.pathFromRoot("zig-out/lib"));
+
+    const check_exe = exe.checkObject(.macho);
+    check_exe.checkStart("cmd LOAD_DYLIB");
+    check_exe.checkNext("name @rpath/liba.dylib");
+    check_exe.checkNext("timestamp 2");
+    check_exe.checkNext("current version 10000");
+    check_exe.checkNext("compatibility version 10000");
+
+    check_exe.checkStart("cmd RPATH");
+    check_exe.checkNext(std.fmt.allocPrint(b.allocator, "path {s}", .{b.pathFromRoot("zig-out/lib")}) catch unreachable);
+
+    test_step.dependOn(&check_exe.step);
+
+    const run = exe.run();
+    run.cwd = b.pathFromRoot(".");
+    run.expectStdOutEqual("Hello world");
+    test_step.dependOn(&run.step);
+}

test/link/macho/dylib/main.c

@@ -0,0 +1,9 @@
+#include <stdio.h>
+
+char* hello();
+extern char world[];
+
+int main() {
+  printf("%s %s", hello(), world);
+  return 0;
+}

test/link/macho/entry/build.zig

@@ -0,0 +1,34 @@
+const std = @import("std");
+const Builder = std.build.Builder;
+
+pub fn build(b: *Builder) void {
+    const mode = b.standardReleaseOptions();
+
+    const test_step = b.step("test", "Test");
+    test_step.dependOn(b.getInstallStep());
+
+    const exe = b.addExecutable("main", null);
+    exe.setBuildMode(mode);
+    exe.addCSourceFile("main.c", &.{});
+    exe.linkLibC();
+    exe.entry_symbol_name = "_non_main";
+
+    const check_exe = exe.checkObject(.macho);
+
+    check_exe.checkStart("segname __TEXT");
+    check_exe.checkNext("vmaddr {vmaddr}");
+
+    check_exe.checkStart("cmd MAIN");
+    check_exe.checkNext("entryoff {entryoff}");
+
+    check_exe.checkInSymtab();
+    check_exe.checkNext("_non_main {n_value}");
+
+    check_exe.checkComputeEq("vmaddr entryoff +", "n_value");
+
+    test_step.dependOn(&check_exe.step);
+
+    const run = exe.run();
+    run.expectStdOutEqual("42");
+    test_step.dependOn(&run.step);
+}

test/link/macho/entry/main.c

@@ -0,0 +1,6 @@
+#include <stdio.h>
+
+int non_main() {
+  printf("%d", 42);
+  return 0;
+}

test/link/macho/frameworks/build.zig

@@ -0,0 +1,32 @@
+const std = @import("std");
+const Builder = std.build.Builder;
+
+pub fn build(b: *Builder) void {
+    const mode = b.standardReleaseOptions();
+
+    const test_step = b.step("test", "Test the program");
+
+    const exe = b.addExecutable("test", null);
+    b.default_step.dependOn(&exe.step);
+    exe.addCSourceFile("main.c", &[0][]const u8{});
+    exe.setBuildMode(mode);
+    exe.linkLibC();
+    exe.linkFramework("Cocoa");
+
+    const check = exe.checkObject(.macho);
+    check.checkStart("cmd LOAD_DYLIB");
+    check.checkNext("name {*}Cocoa");
+
+    switch (mode) {
+        .Debug, .ReleaseSafe => {
+            check.checkStart("cmd LOAD_DYLIB");
+            check.checkNext("name {*}libobjc{*}.dylib");
+        },
+        else => {},
+    }
+
+    test_step.dependOn(&check.step);
+
+    const run_cmd = exe.run();
+    test_step.dependOn(&run_cmd.step);
+}

test/link/macho/objc/build.zig

@@ -1,19 +1,8 @@
 const std = @import("std");
 const Builder = std.build.Builder;
-const CrossTarget = std.zig.CrossTarget;
-
-fn isRunnableTarget(t: CrossTarget) bool {
-    // TODO I think we might be able to run this on Linux via Darling.
-    // Add a check for that here, and return true if Darling is available.
-    if (t.isNative() and t.getOsTag() == .macos)
-        return true
-    else
-        return false;
-}
 
 pub fn build(b: *Builder) void {
     const mode = b.standardReleaseOptions();
-    const target = b.standardTargetOptions(.{});
 
     const test_step = b.step("test", "Test the program");
 
@@ -23,14 +12,11 @@ pub fn build(b: *Builder) void {
     exe.addCSourceFile("Foo.m", &[0][]const u8{});
     exe.addCSourceFile("test.m", &[0][]const u8{});
     exe.setBuildMode(mode);
-    exe.setTarget(target);
     exe.linkLibC();
     // TODO when we figure out how to ship framework stubs for cross-compilation,
     // populate paths to the sysroot here.
     exe.linkFramework("Foundation");
 
-    if (isRunnableTarget(target)) {
-        const run_cmd = exe.run();
-        test_step.dependOn(&run_cmd.step);
-    }
+    const run_cmd = exe.run();
+    test_step.dependOn(&run_cmd.step);
 }

test/link/macho/objcpp/build.zig

@@ -1,19 +1,8 @@
 const std = @import("std");
 const Builder = std.build.Builder;
-const CrossTarget = std.zig.CrossTarget;
-
-fn isRunnableTarget(t: CrossTarget) bool {
-    // TODO I think we might be able to run this on Linux via Darling.
-    // Add a check for that here, and return true if Darling is available.
-    if (t.isNative() and t.getOsTag() == .macos)
-        return true
-    else
-        return false;
-}
 
 pub fn build(b: *Builder) void {
     const mode = b.standardReleaseOptions();
-    const target = b.standardTargetOptions(.{});
 
     const test_step = b.step("test", "Test the program");
 
@@ -23,14 +12,13 @@ pub fn build(b: *Builder) void {
     exe.addCSourceFile("Foo.mm", &[0][]const u8{});
     exe.addCSourceFile("test.mm", &[0][]const u8{});
     exe.setBuildMode(mode);
-    exe.setTarget(target);
     exe.linkLibCpp();
     // TODO when we figure out how to ship framework stubs for cross-compilation,
     // populate paths to the sysroot here.
     exe.linkFramework("Foundation");
 
-    if (isRunnableTarget(target)) {
-        const run_cmd = exe.run();
-        test_step.dependOn(&run_cmd.step);
-    }
+    const run_cmd = exe.run();
+    run_cmd.expectStdOutEqual("Hello from C++ and Zig");
+
+    test_step.dependOn(&run_cmd.step);
 }

test/link/macho/pagezero/build.zig

@@ -0,0 +1,43 @@
+const std = @import("std");
+const Builder = std.build.Builder;
+
+pub fn build(b: *Builder) void {
+    const mode = b.standardReleaseOptions();
+
+    const test_step = b.step("test", "Test");
+    test_step.dependOn(b.getInstallStep());
+
+    {
+        const exe = b.addExecutable("pagezero", null);
+        exe.setBuildMode(mode);
+        exe.addCSourceFile("main.c", &.{});
+        exe.linkLibC();
+        exe.pagezero_size = 0x4000;
+
+        const check = exe.checkObject(.macho);
+        check.checkStart("LC 0");
+        check.checkNext("segname __PAGEZERO");
+        check.checkNext("vmaddr 0");
+        check.checkNext("vmsize 4000");
+
+        check.checkStart("segname __TEXT");
+        check.checkNext("vmaddr 4000");
+
+        test_step.dependOn(&check.step);
+    }
+
+    {
+        const exe = b.addExecutable("no_pagezero", null);
+        exe.setBuildMode(mode);
+        exe.addCSourceFile("main.c", &.{});
+        exe.linkLibC();
+        exe.pagezero_size = 0;
+
+        const check = exe.checkObject(.macho);
+        check.checkStart("LC 0");
+        check.checkNext("segname __TEXT");
+        check.checkNext("vmaddr 0");
+
+        test_step.dependOn(&check.step);
+    }
+}

test/link/macho/pagezero/main.c

@@ -0,0 +1,3 @@
+int main(int argc, char* argv[]) {
+  return 0;
+}

test/link/macho/stack_size/build.zig

@@ -0,0 +1,24 @@
+const std = @import("std");
+const Builder = std.build.Builder;
+
+pub fn build(b: *Builder) void {
+    const mode = b.standardReleaseOptions();
+
+    const test_step = b.step("test", "Test");
+    test_step.dependOn(b.getInstallStep());
+
+    const exe = b.addExecutable("main", null);
+    exe.setBuildMode(mode);
+    exe.addCSourceFile("main.c", &.{});
+    exe.linkLibC();
+    exe.stack_size = 0x100000000;
+
+    const check_exe = exe.checkObject(.macho);
+    check_exe.checkStart("cmd MAIN");
+    check_exe.checkNext("stacksize 100000000");
+
+    test_step.dependOn(&check_exe.step);
+
+    const run = exe.run();
+    test_step.dependOn(&run.step);
+}

test/link/macho/stack_size/main.c

@@ -0,0 +1,3 @@
+int main(int argc, char* argv[]) {
+  return 0;
+}

test/link/tls/a.c

@@ -0,0 +1,5 @@
+_Thread_local int a;
+
+int getA() {
+  return a;
+}

test/link/tls/build.zig

@@ -6,10 +6,12 @@ pub fn build(b: *Builder) void {
     const lib = b.addSharedLibrary("a", null, b.version(1, 0, 0));
     lib.setBuildMode(mode);
     lib.addCSourceFile("a.c", &.{});
+    lib.linkLibC();
 
     const test_exe = b.addTest("main.zig");
     test_exe.setBuildMode(mode);
     test_exe.linkLibrary(lib);
+    test_exe.linkLibC();
 
     const test_step = b.step("test", "Test it");
     test_step.dependOn(&test_exe.step);

test/link/tls/main.zig

@@ -0,0 +1,15 @@
+const std = @import("std");
+
+extern threadlocal var a: i32;
+extern fn getA() i32;
+
+fn getA2() i32 {
+    return a;
+}
+
+test {
+    a = 2;
+    try std.testing.expect(getA() == 2);
+    try std.testing.expect(2 == getA2());
+    try std.testing.expect(getA() == getA2());
+}

test/standalone.zig

@@ -13,31 +13,12 @@ pub fn addCases(cases: *tests.StandaloneContext) void {
     cases.addBuildFile("test/standalone/main_pkg_path/build.zig", .{});
     cases.addBuildFile("test/standalone/shared_library/build.zig", .{});
     cases.addBuildFile("test/standalone/mix_o_files/build.zig", .{});
-    if (builtin.os.tag == .macos) {
-        // Zig's macOS linker does not yet support LTO for LLVM IR files:
-        // https://github.com/ziglang/zig/issues/8680
-        cases.addBuildFile("test/standalone/mix_c_files/build.zig", .{
-            .build_modes = false,
-            .cross_targets = true,
-        });
-    } else {
-        cases.addBuildFile("test/standalone/mix_c_files/build.zig", .{
-            .build_modes = true,
-            .cross_targets = true,
-        });
-    }
+    cases.addBuildFile("test/standalone/mix_c_files/build.zig", .{
+        .build_modes = true,
+        .cross_targets = true,
+    });
     cases.addBuildFile("test/standalone/global_linkage/build.zig", .{});
     cases.addBuildFile("test/standalone/static_c_lib/build.zig", .{});
-    cases.addBuildFile("test/standalone/link_interdependent_static_c_libs/build.zig", .{});
-    cases.addBuildFile("test/standalone/link_static_lib_as_system_lib/build.zig", .{});
-    cases.addBuildFile("test/standalone/link_common_symbols/build.zig", .{});
-    cases.addBuildFile("test/standalone/link_frameworks/build.zig", .{
-        .requires_macos_sdk = true,
-    });
-    cases.addBuildFile("test/standalone/link_common_symbols_alignment/build.zig", .{});
-    if (builtin.os.tag == .macos) {
-        cases.addBuildFile("test/standalone/link_import_tls_dylib/build.zig", .{});
-    }
     cases.addBuildFile("test/standalone/issue_339/build.zig", .{});
     cases.addBuildFile("test/standalone/issue_8550/build.zig", .{});
     cases.addBuildFile("test/standalone/issue_794/build.zig", .{});
@@ -69,16 +50,6 @@ pub fn addCases(cases: *tests.StandaloneContext) void {
     if (builtin.os.tag == .linux) {
         cases.addBuildFile("test/standalone/pie/build.zig", .{});
     }
-    // Try to build and run an Objective-C executable.
-    cases.addBuildFile("test/standalone/objc/build.zig", .{
-        .build_modes = true,
-        .requires_macos_sdk = true,
-    });
-    // Try to build and run an Objective-C++ executable.
-    cases.addBuildFile("test/standalone/objcpp/build.zig", .{
-        .build_modes = true,
-        .requires_macos_sdk = true,
-    });
 
     // Ensure the development tools are buildable.
     cases.add("tools/gen_spirv_spec.zig");

test/standalone/link_frameworks/build.zig

@@ -1,34 +0,0 @@
-const std = @import("std");
-const Builder = std.build.Builder;
-const CrossTarget = std.zig.CrossTarget;
-
-fn isRunnableTarget(t: CrossTarget) bool {
-    // TODO I think we might be able to run this on Linux via Darling.
-    // Add a check for that here, and return true if Darling is available.
-    if (t.isNative() and t.getOsTag() == .macos)
-        return true
-    else
-        return false;
-}
-
-pub fn build(b: *Builder) void {
-    const mode = b.standardReleaseOptions();
-    const target = b.standardTargetOptions(.{});
-
-    const test_step = b.step("test", "Test the program");
-
-    const exe = b.addExecutable("test", null);
-    b.default_step.dependOn(&exe.step);
-    exe.addCSourceFile("main.c", &[0][]const u8{});
-    exe.setBuildMode(mode);
-    exe.setTarget(target);
-    exe.linkLibC();
-    // TODO when we figure out how to ship framework stubs for cross-compilation,
-    // populate paths to the sysroot here.
-    exe.linkFramework("Cocoa");
-
-    if (isRunnableTarget(target)) {
-        const run_cmd = exe.run();
-        test_step.dependOn(&run_cmd.step);
-    }
-}

test/standalone/link_import_tls_dylib/a.c

@@ -1 +0,0 @@
-_Thread_local int a;

test/standalone/link_import_tls_dylib/main.zig

@@ -1,7 +0,0 @@
-const std = @import("std");
-
-extern threadlocal var a: i32;
-
-test {
-    try std.testing.expect(a == 0);
-}

test/tests.zig

@@ -21,6 +21,7 @@ const assemble_and_link = @import("assemble_and_link.zig");
 const translate_c = @import("translate_c.zig");
 const run_translated_c = @import("run_translated_c.zig");
 const gen_h = @import("gen_h.zig");
+const link = @import("link.zig");
 
 // Implementations
 pub const TranslateCContext = @import("src/translate_c.zig").TranslateCContext;
@@ -479,6 +480,27 @@ pub fn addStandaloneTests(
     return cases.step;
 }
 
+pub fn addLinkTests(
+    b: *build.Builder,
+    test_filter: ?[]const u8,
+    modes: []const Mode,
+    enable_macos_sdk: bool,
+) *build.Step {
+    const cases = b.allocator.create(StandaloneContext) catch unreachable;
+    cases.* = StandaloneContext{
+        .b = b,
+        .step = b.step("test-link", "Run the linker tests"),
+        .test_index = 0,
+        .test_filter = test_filter,
+        .modes = modes,
+        .skip_non_native = true,
+        .enable_macos_sdk = enable_macos_sdk,
+        .target = .{},
+    };
+    link.addCases(cases);
+    return cases.step;
+}
+
 pub fn addCliTests(b: *build.Builder, test_filter: ?[]const u8, modes: []const Mode) *build.Step {
     _ = test_filter;
     _ = modes;
@@ -973,7 +995,8 @@ pub const StandaloneContext = struct {
         }
 
         if (features.cross_targets and !self.target.isNative()) {
-            const target_arg = fmt.allocPrint(b.allocator, "-Dtarget={s}", .{self.target.zigTriple(b.allocator) catch unreachable}) catch unreachable;
+            const target_triple = self.target.zigTriple(b.allocator) catch unreachable;
+            const target_arg = fmt.allocPrint(b.allocator, "-Dtarget={s}", .{target_triple}) catch unreachable;
             zig_args.append(target_arg) catch unreachable;
         }