Make GN Android build link executables

build/toolchain/android/BUILD.gn

 # Copyright 2013 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/config/android/config.gni")
+import("//build/config/sysroot.gni")  # Imports android/config.gni.
 import("//build/toolchain/clang.gni")
 import("//build/toolchain/goma.gni")
 import("//build/toolchain/gcc_toolchain.gni")
 
-# Get the Android version of the name of the build host's architecture.
-if (build_cpu_arch == "x64") {
-  android_host_arch = "x86_64"
-} else if (build_cpu_arch == "x86") {
-  android_host_arch = "x86"
-} else {
-  assert(false, "Need Android toolchain support for your build OS.")
+android_ndk_lib = sysroot + "android_ndk_lib_dir"
+
+# The Android GCC toolchains share most of the same parameters, so we have this
+# wrapper around gcc_toolchain to avoid duplication of logic.
+#
+# Parameters:
+#  - android_ndk_sysroot
+#      Sysroot for this architecture.
+#  - android_ndk_lib_dir
+#      Subdirectory inside of android_ndk_sysroot where libs go.
+#  - tool_prefix
+#      Prefix to be added to the tool names.
+#  - toolchain_cpu_arch
+#      Same as gcc_toolchain
+template("android_gcc_toolchain") {
+  gcc_toolchain(target_name) {
+    # Make our manually injected libs relative to the build dir.
+    android_ndk_lib = rebase_path(
+      invoker.android_ndk_sysroot + "/" + invoker.android_ndk_lib_dir,
+      root_build_dir)
+
+    libs_section_prefix = "$android_ndk_lib/crtbegin_dynamic.o"

[awong, 2014/05/12 19:23:02]

I think you might be able to kill this if you don't use nostdlib

+    libs_section_postfix = "$android_ndk_lib/crtend_android.o"
+
+    # The tools should be run relative to the build dir.
+    tool_prefix = rebase_path(invoker.tool_prefix, root_build_dir)
+
+    cc = tool_prefix + "gcc"
+    cxx = tool_prefix + "g++"
+    ar = tool_prefix + "ar"
+    ld = cxx
+
+    toolchain_os = "android"
+    toolchain_cpu_arch = invoker.toolchain_cpu_arch
+  }
 }
 
-gcc_toolchain("x86") {
-  prefix = "$android_ndk_root/toolchains/x86-4.6/prebuilt/$build_os-$android_host_arch/bin/i686-linux-android-"
-  cc  = prefix + "gcc"
-  cxx = prefix + "g++"
-  ar  = prefix + "ar"
-  ld  = cxx
+android_gcc_toolchain("x86") {
+  android_ndk_sysroot = "$android_ndk_root/$x86_android_sysroot_subdir"
+  android_ndk_lib_dir = "usr/lib"
 
+  tool_prefix = "$x86_android_toolchain_root/bin/i686-linux-android-"

[awong, 2014/05/12 19:23:02]

Is there a reason the tool_prefix is here rather than in config.gni? Just
limiting the visibility of the symbol?

Also, longer term, I wonder if we should just make *all* of Chrome gcc/clang
toolchains build using the fully qualified platform triple names for the tools
(i686-linux-android-gcc, etc) rather than the shorthand "gcc/g++, etc"

If we always treat ourselves as a cross-compiler configuration even when
host==target, we may cut down some complexity. IIRC, Google3 is setup this way.

[brettw, 2014/05/12 21:00:08]

Yes, because it's different in every toolchain in this file. This file is
executed once in the context of default toolchain to define to the toolchains,
and it defines all of them. Otherwise there is a chicken-and-egg problem.

   toolchain_cpu_arch = "x86"
-  toolchain_os = "android"
 }
 
-gcc_toolchain("arm") {
-  prefix = "$android_ndk_root/toolchains/arm-linux-androideabi-4.6/prebuilt/$build_os-$android_host_arch/bin/arm-linux-androideabi-"
-  cc  = prefix + "gcc"
-  cxx = prefix + "g++"
-  ar  = prefix + "ar"
-  ld  = cxx
+android_gcc_toolchain("arm") {
+  android_ndk_sysroot = "$android_ndk_root/$arm_android_sysroot_subdir"
+  android_ndk_lib_dir = "usr/lib"
 
+  tool_prefix = "$arm_android_toolchain_root/bin/arm-linux-androideabi-"
   toolchain_cpu_arch = "arm"
-  toolchain_os = "android"
 }
 
-gcc_toolchain("mipsel") {
-  prefix = "$android_ndk_root/toolchains/mipsel-linux-android-4.6/prebuilt/$build_os-$android_host_arch/bin/mipsel-linux-android-"
-  cc  = prefix + "gcc"
-  cxx = prefix + "g++"
-  ar  = prefix + "ar"
-  ld  = cxx
+android_gcc_toolchain("mipsel") {
+  android_ndk_sysroot = "$android_ndk_root/$mips_android_sysroot_subdir"
+  android_ndk_lib_dir = "usr/lib"
 
+  tool_prefix = "$mips_android_toolchain_root/bin/mipsel-linux-android-"
   toolchain_cpu_arch = "mipsel"
-  toolchain_os = "android"
 }