[linux] Improve link time with Chromium-bundled binutils.

build/toolchain.gypi

 # Copyright 2013 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 68 matching lines @@
     'v8_toolset_for_d8%': 'target',
 
     'host_os%': '<(OS)',
     'werror%': '-Werror',
     # For a shared library build, results in "libv8-<(soname_version).so".
     'soname_version%': '',
 
     # Allow to suppress the array bounds warning (default is no suppression).
     'wno_array_bounds%': '',
 
+    # Override where to find binutils
+    'binutils_dir%': '',
+
+    'conditions': [
+      ['OS=="linux" and host_arch=="x64"', {
+        'binutils_dir%': 'third_party/binutils/Linux_x64/Release/bin',
+      }],
+      ['OS=="linux" and host_arch=="ia32"', {
+        'binutils_dir%': 'third_party/binutils/Linux_ia32/Release/bin',
+      }],
+
+      # linux_use_bundled_gold: whether to use the gold linker binary checked
+      # into third_party/binutils.  Force this off via GYP_DEFINES when you
+      # are using a custom toolchain and need to control -B in ldflags.
+      # Do not use 32-bit gold on 32-bit hosts as it runs out address space
+      # for component=static_library builds.
+      ['OS=="linux" and (target_arch=="x64" or target_arch=="arm")', {
+        'linux_use_bundled_gold%': 1,
+      }, {
+        'linux_use_bundled_gold%': 0,
+      }],
+      # linux_use_bundled_binutils: whether to use the binary binutils
+      # checked into third_party/binutils.  These are not multi-arch so cannot
+      # be used except on x86 and x86-64 (the only two architectures which
+      # are currently checke in).  Force this off via GYP_DEFINES when you
+      # are using a custom toolchain and need to control -B in cflags.
+      ['OS=="linux" and (target_arch=="ia32" or target_arch=="x64")', {
+        'linux_use_bundled_binutils%': 1,
+      }, {
+        'linux_use_bundled_binutils%': 0,
+      }],
+      # linux_use_gold_flags: whether to use build flags that rely on gold.
+      # On by default for x64 Linux.
+      ['OS=="linux" and target_arch=="x64"', {
+        'linux_use_gold_flags%': 1,
+      }, {
+        'linux_use_gold_flags%': 0,
+      }],
+    ],
+
     # Link-Time Optimizations
     'use_lto%': 0,
 
     'variables': {
       # This is set when building the Android WebView inside the Android build
       # system, using the 'android' gyp backend.
       'android_webview_build%': 0,
     },
     # Copy it out one scope.
     'android_webview_build%': '<(android_webview_build)',
@@ skipping 691 matching lines @@
         ],
         'cflags': [
           '-mx32',
           # Inhibit warning if long long type is used.
           '-Wno-long-long',
         ],
         'ldflags': [
           '-mx32',
         ],
       }],  # v8_target_arch=="x32"
+      ['linux_use_gold_flags==1', {
+        # Newer gccs and clangs support -fuse-ld, use the flag to force gold
+        # selection.
+        # gcc -- http://gcc.gnu.org/onlinedocs/gcc-4.8.0/gcc/Optimize-Options.html
+        'ldflags': [ '-fuse-ld=gold', ],
+      }],
+      ['linux_use_bundled_binutils==1', {
+        'cflags': [
+          '-B<!(cd <(DEPTH) && pwd -P)/<(binutils_dir)',
+        ],
+      }],
+      ['linux_use_bundled_gold==1', {
+        # Put our binutils, which contains gold in the search path. We pass
+        # the path to gold to the compiler. gyp leaves unspecified what the
+        # cwd is when running the compiler, so the normal gyp path-munging
+        # fails us. This hack gets the right path.
+        'ldflags': [
+          '-B<!(cd <(DEPTH) && pwd -P)/<(binutils_dir)',
+        ],
+      }],
       ['OS=="win"', {
         'defines': [
           'WIN32',
         ],
         # 4351: VS 2005 and later are warning us that they've fixed a bug
         #       present in VS 2003 and earlier.
         'msvs_disabled_warnings': [4351],
         'msvs_configuration_attributes': {
           'OutputDirectory': '<(DEPTH)\\build\\$(ConfigurationName)',
           'IntermediateDirectory': '$(OutDir)\\obj\\$(ProjectName)',
@@ skipping 266 matching lines @@
               ['android_full_debug==0', {
                 # Disable full debug if we want a faster v8 in a debug build.
                 # TODO(2304): pass DISABLE_DEBUG_ASSERT instead of hiding DEBUG.
                 'defines!': [
                   'DEBUG',
                   'ENABLE_SLOW_DCHECKS',
                 ],
               }],
             ],
           }],
+          ['linux_use_gold_flags==1', {
+            'target_conditions': [
+              ['_toolset=="target"', {
+                'ldflags': [
+                  # Experimentation found that using four linking threads
+                  # saved ~20% of link time.
+                  # https://groups.google.com/a/chromium.org/group/chromium-dev/browse_thread/thread/281527606915bb36
+                  # Only apply this to the target linker, since the host
+                  # linker might not be gold, but isn't used much anyway.
+                  '-Wl,--threads',
+                  '-Wl,--thread-count=4',
+                ],
+              }],
+            ],
+          }],
         ],
       },  # DebugBaseCommon
       'Debug': {
         'inherit_from': ['DebugBaseCommon'],
         'conditions': [
           ['v8_optimized_debug==0', {
             'inherit_from': ['DebugBase0'],
           }, {
             'inherit_from': ['DebugBase1'],
           }],
@@ skipping 75 matching lines @@
           ['v8_enable_slow_dchecks==1', {
             'defines': [
               'ENABLE_SLOW_DCHECKS',
             ],
           }],
         ],  # conditions
       },  # Release
     },  # configurations
   },  # target_defaults
 }