Rework the way ChromiumOS toolchains will work in GN.

build/toolchain/cros/BUILD.gn

 # 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.
 
 import("//build/toolchain/gcc_toolchain.gni")
 
 # CrOS builds must cross-compile on a Linux host for the actual CrOS
 # device target. There are many different CrOS devices so the build
 # system provides configuration variables that permit a CrOS build to
 # control the cross-compilation tool chain. However, requiring such
@@ skipping 18 matching lines @@
 #
 # goma_dir = "/g/.cros_cache/common/goma+2"
 # target_sysroot= /g/.cros_cache/chrome-sdk/tarballs/auron_paine+7644.0.0+sysroot_chromeos-base_chromeos-chrome.tar.xz"
 # cros_target_cc = "x86_64-cros-linux-gnu-gcc -B/g/.cros_cache/chrome-sdk/tarballs/auron_paine+7657.0.0+target_toolchain/usr/x86_64-pc-linux-gnu/x86_64-cros-linux-gnu/binutils-bin/2.25.51-gold"
 # cros_target_cxx = "x86_64-cros-linux-gnu-g++ -B/g/.cros_cache/chrome-sdk/tarballs/auron_paine+7657.0.0+target_toolchain/usr/x86_64-pc-linux-gnu/x86_64-cros-linux-gnu/binutils-bin/2.25.51-gold"
 # cros_target_ar = "x86_64-cros-linux-gnu-gcc-ar"
 # target_cpu = "x64"
 
 declare_args() {
   # These must be specified for a board-specific build.
-  cros_target_cc = ""
-  cros_target_cxx = ""
-  cros_target_ar = ""
+  cros_target_ar = "ar"
+  cros_target_cc = "gcc"
+  cros_target_cxx = "g++"
+  cros_target_ld = ""
+
+  # These can be optionally set.
+  cros_target_extra_cflags = ""
+  cros_target_extra_cppflags = ""
+  cros_target_extra_cxxflags = ""
+  cros_target_extra_ldflags = ""
+
+  # is_clang is used instead of cros_target_is_clang
+
+  cros_host_ar = "ar"
+  cros_host_cc = "gcc"
+  cros_host_cxx = "g++"
+  cros_host_ld = ""
+  cros_host_extra_cflags = ""
+  cros_host_extra_cppflags = ""
+  cros_host_extra_cxxflags = ""
+  cros_host_extra_ldflags = ""
+  cros_host_is_clang = false
+
+  cros_v8_snapshot_ar = "ar"
+  cros_v8_snapshot_cc = "gcc"
+  cros_v8_snapshot_cxx = "g++"
+  cros_v8_snapshot_ld = ""
+  cros_v8_snapshot_extra_cflags = ""
+  cros_v8_snapshot_extra_cppflags = ""
+  cros_v8_snapshot_extra_cxxflags = ""
+  cros_v8_snapshot_extra_ldflags = ""
+  cros_v8_snapshot_is_clang = false
 }
 
+# TODO(dpranke): Delete this after we get rid of the reference to
+# build/toolchain/cros:clang_target in BUILDCONFIG.gn
 clang_toolchain("clang_target") {
   toolchain_cpu = target_cpu
   toolchain_os = "linux"
 }
 
 gcc_toolchain("target") {
-  # These defaults permit building on a Linux host as described above.
-  cc = "gcc"
-  cxx = "g++"
-  ar = "ar"
+  # TODO(dpranke): change the cros_target_{cc,cxx,ar} vars to default
+  # to empty strings, and then assert that they are non-empty (i.e.,
+  # set in args.gn) once we get rid of the reference to
+  # build/toolchain/cros:target in BUILDCONFIG.gn

[hashimoto, 2016/05/17 06:26:31]

How are we going to use this toolchain after removing the references to
cros:target and cros:clang_target from BUILDCONFIG.gn (IIUC it's going to use
linux:target and linux:clang_target even when target_os=="chromeos")?
By specifying custom_toolchain?

[hashimoto, 2016/05/18 03:24:01]

ping?

[Dirk Pranke, 2016/05/18 04:12:12]

That's weird, I thought I wrote an answer for this.

This TODO is wrong and should be deleted. We're keeping the cros:target
toolchain, and we have more sensible defaults now.

 
-  # But to build for a specific board, the cros_* args will need to be defined.
-  if (cros_target_cc != "") {
-    cc = "${cros_target_cc}"
+  # These are args for the template.
+  cc = cros_target_cc
+  cxx = cros_target_cxx
+  ar = cros_target_ar
+  ld = cxx
+  if (cros_target_ld != "") {
+    ld = cros_target_ld
   }
-  if (cros_target_cxx != "") {
-    cxx = "${cros_target_cxx}"
-  }
-  if (cros_target_ar != "") {
-    ar = "${cros_target_ar}"
-  }
-  ld = cxx
+  extra_cflags = cros_target_extra_cflags
+  extra_cppflags = cros_target_extra_cppflags
+  extra_cxxflags = cros_target_extra_cxxflags
+  extra_ldflags = cros_target_extra_ldflags
 
+  # These are passed through as toolchain_args.
+  cc_wrapper = ""
+  is_clang = is_clang
   toolchain_cpu = target_cpu
   toolchain_os = "linux"
-  is_clang = is_clang
+}
+
+gcc_toolchain("host") {
+  # These are args for the template.
+  ar = cros_host_ar

[hashimoto, 2016/05/17 06:26:31]

nit: Please make the order consistent ("cc cxx ar ld" or "ar cc cxx ld") among
all three toolchains.

[Dirk Pranke, 2016/05/17 21:37:45]

Yup, that's unintentionally different. Will fix.

+  cc = cros_host_cc
+  cxx = cros_host_cxx
+  ld = cxx
+  if (cros_host_ld != "") {
+    ld = cros_host_ld
+  }
+  extra_cflags = cros_host_extra_cflags
+  extra_cppflags = cros_host_extra_cppflags
+  extra_cxxflags = cros_host_extra_cxxflags
+  extra_ldflags = cros_host_extra_ldflags
+
+  # These are passed through as toolchain_args.
   cc_wrapper = ""
+  is_clang = cros_host_is_clang
+  toolchain_cpu = host_cpu
+  toolchain_os = "linux"
+  use_sysroot = false
 }
+
+gcc_toolchain("v8_snapshot") {
+  # These are args for the template.
+  ar = cros_v8_snapshot_ar
+  cc = cros_v8_snapshot_cc
+  cxx = cros_v8_snapshot_cxx
+  ld = cxx
+  if (cros_v8_snapshot_ld != "") {
+    ld = cros_v8_snapshot_ld
+  }
+  extra_cflags = cros_v8_snapshot_extra_cflags
+  extra_cppflags = cros_v8_snapshot_extra_cppflags
+  extra_cxxflags = cros_v8_snapshot_extra_cxxflags
+  extra_ldflags = cros_v8_snapshot_extra_ldflags
+
+  # These are passed through as toolchain_args.
+  cc_wrapper = ""
+  is_clang = cros_v8_snapshot_is_clang
+  if (target_cpu == "x86" || target_cpu == "arm" || target_cpu == "mipsel") {
+    toolchain_cpu = "x86"
+  } else {
+    toolchain_cpu = "x64"
+  }
+  toolchain_os = "linux"
+  use_sysroot = false
+}