Make GN Android build link executables

build/config/android/config.gni

Index: build/config/android/config.gni
diff --git a/build/config/android/config.gni b/build/config/android/config.gni
index 6a9080bcf86c93da40ff1b7c30f4370dd876412b..f7d7dac49896b332794519cf681c7625ba97696d 100644
--- a/build/config/android/config.gni
+++ b/build/config/android/config.gni
@@ -20,10 +20,62 @@ if (is_android) {
            "You must specify android_src for an Android WebView build.")
   }
 
-  # android_ndk_root -----------------------------------------------------------
+  # Host stuff -----------------------------------------------------------------

[scottmg, 2014/05/12 16:33:58]

i have no idea about any of this file

 
-  # Full system path to the Android NDK.
-  android_ndk_root = rebase_path("//third_party/android_tools/ndk")
+  # Defines the name the Android build gives to the current host CPU
+  # architecture, which is different than the names GN uses.
+  if (build_cpu_arch == "x64") {
+    android_host_arch = "x86_64"

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

ick. Is this actually a variable we wish to expose beyond the toolchain config?
If not, maybe use _android_host_arch?

Same with android_host_os.

Somethings I wonder if there should be a "local" declaration on a symbol that
keeps it scoped to a single file (eg, doesn't even transit include)

+  } else if (build_cpu_arch == "x86") {
+    android_host_arch = "x86"
+  } else {
+    assert(false, "Need Android toolchain support for your build CPU arch.")
+  }
+
+  # Defines the name the Android build gives to the current host CPU
+  # architecture, which is different than the names GN uses.
+  if (build_os == "linux") {
+    android_host_os = "linux"

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

Are there other android_host_os values that we will be adding in the future?
Maybe add a TODO? As is, it looks like we should just assert build_os == "linux"
and not have the extra level of indirection.

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

They're working on Mac.

+  } else {
+    assert(false, "Need Android toolchain support for your build OS.")
+  }
+
+  # Directories and files ------------------------------------------------------
+  #
+  # We define may of the dirs strings here for each output architecture (rather
+  # than just the current one) since these are needed by the Android toolchain
+  # file to define toolchains for all possible targets in one pass.
+
+  # Path to the Android NDK.
+  android_ndk_root = "//third_party/android_tools/ndk"

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

Not for this CL, but FYI, at some point the ndk root might want be overrideable.

+
+  # Subdirectories inside android_ndk_root that contain the sysroot for the
+  # associated platform.
+  x86_android_sysroot_subdir = "platforms/android-14/arch-x86"

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

Pull 14 out int a _android_api_level variable or something.

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

Done.

+  arm_android_sysroot_subdir = "platforms/android-14/arch-arm"
+  mips_android_sysroot_subdir = "platforms/android-14/arch-mips"

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

Why do we have a different variable exposed for each cpu architecture?

Are there build configurations where I'm targeting arm and need to read the maps
sysroot or something? If not, it feels like we should just be exposing a single
"android_sysroot_subdir".

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

Yes, these all need to be here since the toolchain file needs all of them (it
sets up all the toolchains at once). This is what I was going for with the
comment under "Directories and files".

+
+  # Toolchain root directory for each build. The actual binaries are inside
+  # a "bin" directory inside of these.
+  x86_android_toolchain_root = "$android_ndk_root/toolchains/x86-4.6/prebuilt/$android_host_os-$android_host_arch"

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

Pull 4.6 out to something like _android_toolchain_version. In the future, this
will become _android_toolchain_version=clang-3.4 or something.

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

Done.

+  arm_android_toolchain_root = "$android_ndk_root/toolchains/arm-linux-androideabi-4.6/prebuilt/$android_host_os-$android_host_arch"
+  mips_android_toolchain_root = "$android_ndk_root/toolchains/mipsel-linux-android-4.6/prebuilt/$android_host_os-$android_host_arch"
+
+  # Location of libgcc. This is only needed for the current GN toolchain, so we
+  # only need to define the current one, rather than one for every platform
+  # like the toolchain roots.

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

Hmm...why do we actually need this? libgcc.a is pretty rare to need explicitly.
Is something compiling with -nostdlib or something crazy?

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

I don't know, I just copied gyp:
https://code.google.com/p/chromium/codesearch#chromium/src/build/common.gypi&...

[cjhopman, 2014/05/12 21:04:19]

AIUI, android builds use -nostdlib simply because that's what the normal Android
ndk does (see
https://chromium.googlesource.com/android_tools/+/master-backup/ndk/build/too...
and other lines in there). It's possible that we could get away with something
simpler like -nodefaultlibs, idk. I also don't know if it is worth diverging
from what the ndk does.

[awong, 2014/05/12 21:34:23]

Hmm...let me talk with NDK team. I thought I had upstreamed a fix for this, but
looking at
https://android.googlesource.com/platform/ndk/+/master/build/tools/builder-fu...
it's still there.

I'm okay ignoring for this CL since we should fix upstream in NDK, then port to
gyp, and then to here anyways.

+  if (cpu_arch == "x86") {
+    android_libgcc_file =
+      "$x86_android_toolchain_root/lib/gcc/i686-linux-android/4.6/libgcc.a"
+  } else if (cpu_arch == "arm") {
+    android_libgcc_file =
+      "$arm_android_toolchain_root/lib/gcc/arm-linux-androideabi/4.6/libgcc.a"
+  } else if (cpu_arch == "mips") {
+    android_libgcc_file =
+      "$mips_android_toolchain_root/lib/gcc/mipsel-linux-android/4.6/libgcc.a"
+  } else {
+    assert(false, "Need android libgcc support for your target arch.")
+  }
 
   # stlport stuff --------------------------------------------------------------