GN: Add an option to build against the Debian wheezy sysroot

Set the environment variable DART_USE_WHEEZY to build against
the wheezy sysroot on Linux.

R=johnmccutchan@google.com

Review URL: https://codereview.chromium.org/2476343004 .

DEPS

@@ -555,6 +555,20 @@ hooks = [
       Var('dart_root') + "/third_party/clang.tar.gz.sha1",
     ],
   },
+  {
+    # Pull Debian wheezy sysroot for i386 Linux
+    'name': 'sysroot_i386',
+    'pattern': '.',
+    'action': ['python', 'sdk/build/linux/sysroot_scripts/install-sysroot.py',
+               '--running-as-hook', --arch', 'i386'],
+  },
+  {
+    # Pull Debian wheezy sysroot for amd64 Linux
+    'name': 'sysroot_amd64',
+    'pattern': '.',
+    'action': ['python', 'sdk/build/linux/sysroot_scripts/install-sysroot.py',
+               '--running-as-hook', '--arch', 'amd64'],
+  },
   {
     # Pull clang if needed or requested via GYP_DEFINES.
     'name': 'gn_clang',

build/.gitignore

@@ -1,2 +1,6 @@
 # Generated file containing information about the VS toolchain on Windows
 win_toolchain.json
+
+# Pulled Debian wheezy sysroots
+linux/debian_wheezy_amd64-sysroot
+linux/debian_wheezy_i386-sysroot

build/config/linux/BUILD.gn

@@ -17,5 +17,14 @@ config("sdk") {
                                sysroot,
                              ],
                              "value") ]
+
+    # When using the pulled wheezy sysroot with gcc, we have to specify these
+    # excplicitly.
+    if (dart_use_wheezy_sysroot && !is_clang) {
+      cflags += [
+        "-I=/usr/include/c++/4.6",
+        "-I=/usr/include/c++/4.6/i486-linux-gnu",
+      ]
+    }
   }
 }

build/config/sysroot.gni

@@ -9,6 +9,20 @@ declare_args() {
   # The absolute path of the sysroot that is applied when compiling using
   # the target toolchain.
   target_sysroot = ""
+
+  # Whether the Debian wheezy sysroot should be used.
+  dart_use_wheezy_sysroot = false
+}
+
+if (is_linux && dart_use_wheezy_sysroot) {
+  if (current_cpu == "x86") {
+    target_sysroot = rebase_path("//build/linux/debian_wheezy_i386-sysroot")
+  } else if (current_cpu == "x64") {
+    target_sysroot = rebase_path("//build/linux/debian_wheezy_amd64-sysroot")
+  } else {
+    print("There is no Debian wheezy sysroot present for $current_cpu")
+    assert(false)
+  }
 }
 
 if (current_toolchain == default_toolchain && target_sysroot != "") {

build/detect_host_arch.py

@@ -0,0 +1,40 @@
+#!/usr/bin/env python
+# Copyright 2014 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""Outputs host CPU architecture in format recognized by gyp."""
+
+import platform
+import re
+import sys
+
+
+def HostArch():
+  """Returns the host architecture with a predictable string."""
+  host_arch = platform.machine()
+
+  # Convert machine type to format recognized by gyp.
+  if re.match(r'i.86', host_arch) or host_arch == 'i86pc':
+    host_arch = 'ia32'
+  elif host_arch in ['x86_64', 'amd64']:
+    host_arch = 'x64'
+  elif host_arch.startswith('arm'):
+    host_arch = 'arm'
+
+  # platform.machine is based on running kernel. It's possible to use 64-bit
+  # kernel with 32-bit userland, e.g. to give linker slightly more memory.
+  # Distinguish between different userland bitness by querying
+  # the python binary.
+  if host_arch == 'x64' and platform.architecture()[0] == '32bit':
+    host_arch = 'ia32'
+
+  return host_arch
+
+def DoMain(_):
+  """Hook to be called from gyp without starting a separate python
+  interpreter."""
+  return HostArch()
+
+if __name__ == '__main__':
+  print DoMain([])

build/linux/sysroot_scripts/install-sysroot.py

@@ -108,18 +108,6 @@ def main():
       print 'Unable to detect host architecture'
       return 1
 
-  if options.running_as_hook and target_arch != 'arm' and target_arch != 'mips':
-    # When run from runhooks, only install the sysroot for an Official Chrome
-    # Linux build, except on ARM where we always use a sysroot.
-    skip_if_defined = ['branding=Chrome', 'buildtype=Official']
-    skip_if_undefined = ['chromeos=1']
-    for option in skip_if_defined:
-      if option not in gyp_defines:
-        return 0
-    for option in skip_if_undefined:
-      if option in gyp_defines:
-        return 0
-
   # The sysroot directory should match the one specified in build/common.gypi.
   # TODO(thestig) Consider putting this else where to avoid having to recreate
   # it on every build.

tools/gn.py

@@ -113,11 +113,15 @@ def to_gn_args(args, mode, arch, target_os):
 
   gn_args['is_asan'] = args.asan and gn_args['is_clang']
 
-  if args.target_sysroot:
-    gn_args['target_sysroot'] = args.target_sysroot
+  # Setup the user-defined sysroot.
+  if gn_args['target_os'] == 'linux' and args.wheezy:
+    gn_args['dart_use_wheezy_sysroot'] = True
+  else:
+    if args.target_sysroot:
+      gn_args['target_sysroot'] = args.target_sysroot
 
-  if args.toolchain_prefix:
-    gn_args['toolchain_prefix'] = args.toolchain_prefix
+    if args.toolchain_prefix:
+      gn_args['toolchain_prefix'] = args.toolchain_prefix
 
   goma_dir = os.environ.get('GOMA_DIR')
   goma_home_dir = os.path.join(os.getenv('HOME', ''), 'goma')
@@ -197,12 +201,16 @@ def ide_switch(host_os):
 
 # Environment variables for default settings.
 DART_USE_ASAN = "DART_USE_ASAN"
-
+DART_USE_WHEEZY = "DART_USE_WHEEZY"
 
 def use_asan():
   return DART_USE_ASAN in os.environ
 
 
+def use_wheezy():
+  return DART_USE_WHEEZY in os.environ
+
+
 def parse_args(args):
   args = args[1:]
   parser = argparse.ArgumentParser(description='A script to run `gn gen`.')
@@ -234,6 +242,14 @@ def parse_args(args):
       help='Disable ASAN',
       dest='asan',
       action='store_false')
+  parser.add_argument('--wheezy',
+      help='Use the Debian wheezy sysroot on Linux',
+      default=use_wheezy(),
+      action='store_true')
+  parser.add_argument('--no-wheezy',
+      help='Disable the Debian wheezy sysroot on Linux',
+      dest='wheezy',
+      action='store_false')
   parser.add_argument('--goma',
       help='Use goma',
       default=True,