[build] Re-add linker flags to create empty section in AOT runtime.

To avoid these flags being applied to unexpected build rules, we
separate them out into a separate config that is then pulled in
explicitly in the `dart_precompiled_runtime{,_product}` executable
rules. Only those two executables need the additional empty section:
the product version because it becomes `dartaotruntime` in the SDK
bundle, and the non-product version because some of our tests build
standalone executables using it.

The linker flags were originally removed due to
https://github.com/flutter/flutter/issues/112687.
With the recent removal of bitcode support from Flutter (see
https://github.com/flutter/flutter/issues/107883), I can build
the `ios_release` target locally without any issue.

This also reverts the clang DEPS changes from CL 256208 (again).

TEST=pkg/dartdev/test/commands/compile_test

Bug: https://github.com/dart-lang/sdk/issues/49783
Cq-Include-Trybots: luci.dart.try:analyzer-mac-release-try,dart-sdk-mac-arm64-try,dart-sdk-mac-try,pkg-mac-release-arm64-try,pkg-mac-release-try,vm-kernel-precomp-mac-product-x64-try,vm-kernel-precomp-nnbd-mac-release-arm64-try
Change-Id: Ie46402ec2eeda23109247eb9d7a64935ec2052cb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/262429
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Tess Strickland <sstrickl@google.com>

DEPS

@@ -74,8 +74,8 @@ vars = {
   # The list of revisions for these tools comes from Fuchsia, here:
   # https://fuchsia.googlesource.com/integration/+/HEAD/toolchain
   # If there are problems with the toolchain, contact fuchsia-toolchain@.
-  "clang_revision": "c2592c374e469f343ecea82d6728609650924259",
-  "gn_revision": "d7c2209cebcfe37f46dba7be4e1a7000ffc342fb",
+  "clang_revision": "60d276923902051192eba692e5312e605c9d9f65",
+  "gn_revision": "0bcd37bd2b83f1a9ee17088037ebdfe6eab6d31a",
 
   # Ninja, runs the build based on files generated by GN.
   "ninja_tag": "version:2@1.11.1.chromium.4",
@@ -474,8 +474,7 @@ deps = {
               "version": "git_revision:" + Var("clang_revision"),
           },
       ],
-      # TODO(https://fxbug.dev/73385): Use arm64 toolchain on arm64 when it exists.
-      "condition": "host_cpu == x64 and host_os == mac or host_cpu == arm64 and host_os == mac",
+      "condition": "host_os == mac", # On ARM64 Macs too because Goma doesn't support the host-arm64 toolchain.
       "dep_type": "cipd",
   },
   Var("dart_root") + "/buildtools/win-x64/clang": {
@@ -498,6 +497,16 @@ deps = {
       "condition": "host_os == 'linux' and host_cpu == 'arm64'",
       "dep_type": "cipd",
   },
+  Var("dart_root") + "/buildtools/mac-arm64/clang": {
+      "packages": [
+          {
+              "package": "fuchsia/third_party/clang/mac-arm64",
+              "version": "git_revision:" + Var("clang_revision"),
+          },
+      ],
+      "condition": "host_os == 'mac' and host_cpu == 'arm64'",
+      "dep_type": "cipd",
+  },
 
   Var("dart_root") + "/third_party/webdriver/chrome": {
     "packages": [

build/config/clang/clang.gni

@@ -2,9 +2,11 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("../../toolchain/goma.gni")
+
 _toolchain_cpu = host_cpu
-if (host_os == "mac") {
-  # TODO(https://fxbug.dev/73385): Use arm64 toolchain on arm64 when it exists.
+if (host_os == "mac" && use_goma) {
+  # Goma does not support ARM64.
   _toolchain_cpu = "x64"
 }
 

build/config/compiler/BUILD.gn

@@ -377,7 +377,10 @@ config("compiler") {
     } else if (is_linux) {
       toolchain_stamp_file =
           "//buildtools/linux-x64/clang/.versions/clang.cipd_version"
-    } else {
+    } else if (is_mac && host_cpu == "arm64") {
+      toolchain_stamp_file =
+          "//buildtools/mac-arm64/clang/.versions/clang.cipd_version"
+    } else if (is_mac) {
       toolchain_stamp_file =
           "//buildtools/mac-x64/clang/.versions/clang.cipd_version"
     }
@@ -548,6 +551,7 @@ if (is_win) {
       "-Wno-microsoft-unqualified-friend",
       "-Wno-unknown-argument",  # icu
       "-Wno-unused-value",  # crashpad
+      "-Wno-deprecated-non-prototype",  # zlib
     ]
   } else {
     default_warning_flags += [
@@ -579,6 +583,7 @@ if (is_win) {
     default_warning_flags += [
       "-Wno-tautological-constant-compare",
       "-Wno-unused-but-set-variable",  # icu
+      "-Wno-deprecated-non-prototype",  # zlib
     ]
   } else {
     default_warning_flags +=

build/toolchain/mac/BUILD.gn

@@ -20,6 +20,15 @@ if (use_goma) {
   goma_prefix = ""
 }
 
+# Goma doesn't support the host-arm64 toolchain, so continue using Rosetta.
+if (host_cpu == "arm64" && !use_goma) {
+  rebased_clang_dir =
+      rebase_path("//buildtools/mac-arm64/clang/bin", root_build_dir)
+} else {
+  rebased_clang_dir =
+      rebase_path("//buildtools/mac-x64/clang/bin", root_build_dir)
+}
+
 # Shared toolchain definition. Invocations should set toolchain_os to set the
 # build args in this definition.
 template("mac_toolchain") {
@@ -211,28 +220,10 @@ template("mac_toolchain") {
   }
 }
 
-# Toolchain used for Mac host targets.
 mac_toolchain("clang_x64") {
   toolchain_cpu = "x64"
   toolchain_os = "mac"
-  prefix = rebase_path("//buildtools/mac-x64/clang/bin", root_build_dir)
-  cc = "${goma_prefix}$prefix/clang"
-  cxx = "${goma_prefix}$prefix/clang++"
-  ar = "${prefix}/llvm-ar"
-  ld = cxx
-  strip = "strip"
-  is_clang = true
-  if (mac_enable_relative_sdk_path) {
-    mac_sdk_path = rebase_path(mac_sdk_path, root_build_dir)
-  }
-  sysroot_flags = "-isysroot $mac_sdk_path -mmacosx-version-min=$mac_sdk_min"
-}
-
-# Toolchain used for Mac host (i386) targets.
-mac_toolchain("clang_x86") {
-  toolchain_cpu = "i386"
-  toolchain_os = "mac"
-  prefix = rebase_path("//buildtools/mac-x64/clang/bin", root_build_dir)
+  prefix = rebased_clang_dir
   cc = "${goma_prefix}$prefix/clang"
   cxx = "${goma_prefix}$prefix/clang++"
   ar = "${prefix}/llvm-ar"
@@ -248,7 +239,7 @@ mac_toolchain("clang_x86") {
 mac_toolchain("clang_arm64") {
   toolchain_cpu = "arm64"
   toolchain_os = "mac"
-  prefix = rebase_path("//buildtools/mac-x64/clang/bin", root_build_dir)
+  prefix = rebased_clang_dir
   cc = "${goma_prefix}$prefix/clang"
   cxx = "${goma_prefix}$prefix/clang++"
   ar = "${prefix}/llvm-ar"

runtime/BUILD.gn

@@ -61,6 +61,24 @@ config("dart_precompiled_runtime_config") {
   ]
 }
 
+config("add_empty_macho_section_config") {
+  if (is_mac) {
+    # We create an empty __space_for_note section in a __CUSTOM segment to
+    # reserve the header space needed for inserting a snapshot into the
+    # executable when creating standalone executables. This segment and section
+    # is removed in standalone executables, replaced with a note that points to
+    # the snapshot in the file.
+    #
+    # (A segment load command with a single section is 132 bytes in 32-bit
+    # executables and 152 bytes in 64-bit ones, and a note load command is
+    # always 40 bytes.)
+    #
+    # Keep this in sync with the constants reservedSegmentName and
+    # reservedSectionName in pkg/dart2native/lib/macho_utils.dart.
+    ldflags = [ "-Wl,-add_empty_section,__CUSTOM,__space_for_note" ]
+  }
+}
+
 # Controls DART_PRECOMPILER #define.
 config("dart_precompiler_config") {
   defines = []

runtime/bin/BUILD.gn

@@ -831,7 +831,10 @@ dart_executable("dart") {
 }
 
 dart_executable("dart_precompiled_runtime") {
-  extra_configs = [ "..:dart_precompiled_runtime_config" ]
+  extra_configs = [
+    "..:dart_precompiled_runtime_config",
+    "..:add_empty_macho_section_config",
+  ]
   extra_deps = [
     "..:libdart_precompiled_runtime",
     "../platform:libdart_platform_precompiled_runtime",
@@ -862,7 +865,10 @@ dart_executable("dart_precompiled_runtime") {
 
 dart_executable("dart_precompiled_runtime_product") {
   use_product_mode = true
-  extra_configs = [ "..:dart_precompiled_runtime_config" ]
+  extra_configs = [
+    "..:dart_precompiled_runtime_config",
+    "..:add_empty_macho_section_config",
+  ]
   extra_deps = [
     "..:libdart_precompiled_runtime_product",
     "../platform:libdart_platform_precompiled_runtime_product",

runtime/vm/malloc_hooks_ia32.cc

@@ -11,9 +11,9 @@
 namespace dart {
 
 #if defined(DEBUG)
-const intptr_t kSkipCount = 6;
+const intptr_t kSkipCount = 7;
 #elif !(defined(PRODUCT) || defined(DEBUG))
-const intptr_t kSkipCount = 5;
+const intptr_t kSkipCount = 6;
 #endif
 
 }  // namespace dart