macho: implement -dead_strip_dylibs linker flag

7 files changed, 31 insertions, 7 deletions

diff --git a/src/Compilation.zig b/src/Compilation.zig
index 652938d741..fffa777f22 100644
--- a/src/Compilation.zig
+++ b/src/Compilation.zig
@@ -911,6 +911,8 @@ pub const InitOptions = struct {
     headerpad_size: ?u32 = null,
     /// (Darwin) set enough space as if all paths were MATPATHLEN
     headerpad_max_install_names: bool = false,
+    /// (Darwin) remove dylibs that are unreachable by the entry point or exported symbols
+    dead_strip_dylibs: bool = false,
 };
 
 fn addPackageTableToCacheHash(
@@ -1754,6 +1756,7 @@ pub fn create(gpa: Allocator, options: InitOptions) !*Compilation {
             .search_strategy = options.search_strategy,
             .headerpad_size = options.headerpad_size,
             .headerpad_max_install_names = options.headerpad_max_install_names,
+            .dead_strip_dylibs = options.dead_strip_dylibs,
         });
         errdefer bin_file.destroy();
         comp.* = .{
@@ -2369,7 +2372,7 @@ fn prepareWholeEmitSubPath(arena: Allocator, opt_emit: ?EmitLoc) error{OutOfMemo
 /// to remind the programmer to update multiple related pieces of code that
 /// are in different locations. Bump this number when adding or deleting
 /// anything from the link cache manifest.
-pub const link_hash_implementation_version = 6;
+pub const link_hash_implementation_version = 7;
 
 fn addNonIncrementalStuffToCacheManifest(comp: *Compilation, man: *Cache.Manifest) !void {
     const gpa = comp.gpa;
@@ -2379,7 +2382,7 @@ fn addNonIncrementalStuffToCacheManifest(comp: *Compilation, man: *Cache.Manifes
     defer arena_allocator.deinit();
     const arena = arena_allocator.allocator();
 
-    comptime assert(link_hash_implementation_version == 6);
+    comptime assert(link_hash_implementation_version == 7);
 
     if (comp.bin_file.options.module) |mod| {
         const main_zig_file = try mod.main_pkg.root_src_directory.join(arena, &[_][]const u8{
@@ -2488,6 +2491,7 @@ fn addNonIncrementalStuffToCacheManifest(comp: *Compilation, man: *Cache.Manifes
     man.hash.addOptional(comp.bin_file.options.search_strategy);
     man.hash.addOptional(comp.bin_file.options.headerpad_size);
     man.hash.add(comp.bin_file.options.headerpad_max_install_names);
+    man.hash.add(comp.bin_file.options.dead_strip_dylibs);
 
     // COFF specific stuff
     man.hash.addOptional(comp.bin_file.options.subsystem);
diff --git a/src/link.zig b/src/link.zig
index 21d54d531c..18e10dc74c 100644
--- a/src/link.zig
+++ b/src/link.zig
@@ -199,6 +199,9 @@ pub const Options = struct {
     /// (Darwin) set enough space as if all paths were MATPATHLEN
     headerpad_max_install_names: bool = false,
 
+    /// (Darwin) remove dylibs that are unreachable by the entry point or exported symbols
+    dead_strip_dylibs: bool = false,
+
     pub fn effectiveOutputMode(options: Options) std.builtin.OutputMode {
         return if (options.use_lld) .Obj else options.output_mode;
     }
diff --git a/src/link/Coff.zig b/src/link/Coff.zig
index 77059a7fd9..0e7d7c89ee 100644
--- a/src/link/Coff.zig
+++ b/src/link/Coff.zig
@@ -969,7 +969,7 @@ fn linkWithLLD(self: *Coff, comp: *Compilation, prog_node: *std.Progress.Node) !
         man = comp.cache_parent.obtain();
         self.base.releaseLock();
 
-        comptime assert(Compilation.link_hash_implementation_version == 6);
+        comptime assert(Compilation.link_hash_implementation_version == 7);
 
         for (self.base.options.objects) |obj| {
             _ = try man.addFile(obj.path, null);
diff --git a/src/link/Elf.zig b/src/link/Elf.zig
index 79545d1e1a..faeb7c9d27 100644
--- a/src/link/Elf.zig
+++ b/src/link/Elf.zig
@@ -1298,7 +1298,7 @@ fn linkWithLLD(self: *Elf, comp: *Compilation, prog_node: *std.Progress.Node) !v
         // We are about to obtain this lock, so here we give other processes a chance first.
         self.base.releaseLock();
 
-        comptime assert(Compilation.link_hash_implementation_version == 6);
+        comptime assert(Compilation.link_hash_implementation_version == 7);
 
         try man.addOptionalFile(self.base.options.linker_script);
         try man.addOptionalFile(self.base.options.version_script);
diff --git a/src/link/MachO.zig b/src/link/MachO.zig
index 4ddee493b8..bd354ba1ce 100644
--- a/src/link/MachO.zig
+++ b/src/link/MachO.zig
@@ -541,7 +541,7 @@ pub fn flushModule(self: *MachO, comp: *Compilation, prog_node: *std.Progress.No
         // We are about to obtain this lock, so here we give other processes a chance first.
         self.base.releaseLock();
 
-        comptime assert(Compilation.link_hash_implementation_version == 6);
+        comptime assert(Compilation.link_hash_implementation_version == 7);
 
         for (self.base.options.objects) |obj| {
             _ = try man.addFile(obj.path, null);
@@ -558,6 +558,7 @@ pub fn flushModule(self: *MachO, comp: *Compilation, prog_node: *std.Progress.No
         man.hash.addOptional(self.base.options.search_strategy);
         man.hash.addOptional(self.base.options.headerpad_size);
         man.hash.add(self.base.options.headerpad_max_install_names);
+        man.hash.add(self.base.options.dead_strip_dylibs);
         man.hash.addListOfBytes(self.base.options.lib_dirs);
         man.hash.addListOfBytes(self.base.options.framework_dirs);
         man.hash.addListOfBytes(self.base.options.frameworks);
@@ -987,6 +988,10 @@ pub fn flushModule(self: *MachO, comp: *Compilation, prog_node: *std.Progress.No
                     try argv.append("-headerpad_max_install_names");
                 }
 
+                if (self.base.options.dead_strip_dylibs) {
+                    try argv.append("-dead_strip_dylibs");
+                }
+
                 if (self.base.options.entry) |entry| {
                     try argv.append("-e");
                     try argv.append(entry);
@@ -1425,7 +1430,12 @@ pub fn parseDylib(self: *MachO, path: []const u8, opts: DylibCreateOpts) ParseDy
     try self.dylibs.append(self.base.allocator, dylib);
     try self.dylibs_map.putNoClobber(self.base.allocator, dylib.id.?.name, dylib_id);
 
-    if (!(opts.is_dependent or self.referenced_dylibs.contains(dylib_id))) {
+    const should_link_dylib_even_if_unreachable = blk: {
+        if (self.base.options.dead_strip_dylibs) break :blk false;
+        break :blk !(opts.is_dependent or self.referenced_dylibs.contains(dylib_id));
+    };
+
+    if (should_link_dylib_even_if_unreachable) {
         try self.addLoadDylibLC(dylib_id);
         try self.referenced_dylibs.putNoClobber(self.base.allocator, dylib_id, {});
     }
diff --git a/src/link/Wasm.zig b/src/link/Wasm.zig
index b074799771..467aa89621 100644
--- a/src/link/Wasm.zig
+++ b/src/link/Wasm.zig
@@ -2546,7 +2546,7 @@ fn linkWithLLD(self: *Wasm, comp: *Compilation, prog_node: *std.Progress.Node) !
         // We are about to obtain this lock, so here we give other processes a chance first.
         self.base.releaseLock();
 
-        comptime assert(Compilation.link_hash_implementation_version == 6);
+        comptime assert(Compilation.link_hash_implementation_version == 7);
 
         for (self.base.options.objects) |obj| {
             _ = try man.addFile(obj.path, null);
diff --git a/src/main.zig b/src/main.zig
index d63e235360..8f9d3e5a13 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -452,6 +452,7 @@ const usage_build_generic =
     \\  -search_dylibs_first           (Darwin) search `libx.dylib` in each dir in library search paths, then `libx.a`
     \\  -headerpad [value]             (Darwin) set minimum space for future expansion of the load commands in hexadecimal notation
     \\  -headerpad_max_install_names   (Darwin) set enough space as if all paths were MAXPATHLEN
+    \\  -dead_strip_dylibs             (Darwin) remove dylibs that are unreachable by the entry point or exported symbols
     \\  --import-memory                (WebAssembly) import memory from the environment
     \\  --import-table                 (WebAssembly) import function table from the host environment
     \\  --export-table                 (WebAssembly) export function table to the host environment
@@ -703,6 +704,7 @@ fn buildOutputType(
     var search_strategy: ?link.File.MachO.SearchStrategy = null;
     var headerpad_size: ?u32 = null;
     var headerpad_max_install_names: bool = false;
+    var dead_strip_dylibs: bool = false;
 
     // e.g. -m3dnow or -mno-outline-atomics. They correspond to std.Target llvm cpu feature names.
     // This array is populated by zig cc frontend and then has to be converted to zig-style
@@ -937,6 +939,8 @@ fn buildOutputType(
                         };
                     } else if (mem.eql(u8, arg, "-headerpad_max_install_names")) {
                         headerpad_max_install_names = true;
+                    } else if (mem.eql(u8, arg, "-dead_strip_dylibs")) {
+                        dead_strip_dylibs = true;
                     } else if (mem.eql(u8, arg, "-T") or mem.eql(u8, arg, "--script")) {
                         linker_script = args_iter.next() orelse {
                             fatal("expected parameter after {s}", .{arg});
@@ -1700,6 +1704,8 @@ fn buildOutputType(
                     };
                 } else if (mem.eql(u8, arg, "-headerpad_max_install_names")) {
                     headerpad_max_install_names = true;
+                } else if (mem.eql(u8, arg, "-dead_strip_dylibs")) {
+                    dead_strip_dylibs = true;
                 } else if (mem.eql(u8, arg, "--gc-sections")) {
                     linker_gc_sections = true;
                 } else if (mem.eql(u8, arg, "--no-gc-sections")) {
@@ -2821,6 +2827,7 @@ fn buildOutputType(
         .search_strategy = search_strategy,
         .headerpad_size = headerpad_size,
         .headerpad_max_install_names = headerpad_max_install_names,
+        .dead_strip_dylibs = dead_strip_dylibs,
     }) catch |err| switch (err) {
         error.LibCUnavailable => {
             const target = target_info.target;