Build 64bit browser for Android with clang for ARMv8

build/config/compiler/BUILD.gn

 # Copyright (c) 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/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/nacl/config.gni")
 import("//build/toolchain/cc_wrapper.gni")
 
-if (current_cpu == "arm") {
+if (current_cpu == "arm" || current_cpu == "arm64") {
   import("//build/config/arm.gni")
 }
 if (current_cpu == "mipsel" || current_cpu == "mips64el") {
   import("//build/config/mips.gni")
 }
 if (is_win) {
   import("//build/config/win/visual_studio_version.gni")
 }
 
 declare_args() {
@@ skipping 604 matching lines @@
       "-mstack-alignment=16",
       "-mstackrealign",
     ]
   }
 }
 
 config("compiler_arm_fpu") {
   if (current_cpu == "arm" && !is_ios && !is_nacl) {
     cflags = [ "-mfpu=$arm_fpu" ]
     asmflags = cflags
+  } else if (current_cpu == "arm64" && !is_ios && !is_nacl) {
+    cflags = [ "-mcpu=$arm_fpu" ]

[Nico, 2016/04/14 15:43:55]

the 32-bit arm branch sets -mfpu, this sets -mcpu. is that intentional?

[khasim.mohammed, 2016/04/14 16:38:46]

-mpu is a 32bit only option, for 64bit mpu is not the correct option, we should
use -mcpu. 

+    asmflags = cflags
   }
 }
 
 # runtime_library -------------------------------------------------------------
 #
 # Sets the runtime library and associated options.
 #
 # How do you determine what should go in here vs. "compiler" above? Consider if
 # a target might choose to use a different runtime library (ignore for a moment
 # if this is possible or reasonable on your system). If such a target would want
@@ skipping 231 matching lines @@
       # http://crbug.com/255186
       "-Wno-deprecated-register",
 
       # TODO(thakis): This used to be implied by -Wno-unused-function,
       # which we no longer use. Check if it makes sense to remove
       # this as well. http://crbug.com/316352
       "-Wno-unneeded-internal-declaration",
 
       # TODO(hans): Get this cleaned up, http://crbug.com/428099
       "-Wno-inconsistent-missing-override",
+      "-Wno-error=unused-command-line-argument",

[Nico, 2016/04/14 15:43:55]

why is this needed?

we want a warning-free build, we don't accept -Wno-error flags. what complains
without this? can we not pass these flags instead?

[khasim.mohammed, 2016/04/14 16:38:46]

I will remove this. It is not needed.

     ]
 
     # NaCl's Clang compiler and Chrome's hermetic Clang compiler will almost
     # always have different versions. Certain flags may not be recognized by
     # one version or the other.
     if (!is_nacl) {
       # Flags NaCl (Clang 3.7) does not recognize.
       cflags += [
         # TODO(thakis): Enable this, crbug.com/507717
         "-Wno-shift-negative-value",
@@ skipping 11 matching lines @@
   if (is_win) {
     cflags = [ "/W4" ]  # Warning level 4.
   } else {
     cflags = [ "-Wall" ]
     if (treat_warnings_as_errors) {
       cflags += [ "-Werror" ]
     }
     if (is_clang) {
       # Enable -Wextra for chromium_code when we control the compiler.
       cflags += [ "-Wextra" ]
+      cflags += [ "-Wno-error=implicit-exception-spec-mismatch" ]
     }
 
     # In Chromium code, we define __STDC_foo_MACROS in order to get the
     # C99 macros on Mac and Linux.
     defines = [
       "__STDC_CONSTANT_MACROS",
       "__STDC_FORMAT_MACROS",
     ]
 
     if (!is_debug && !using_sanitizer &&
@@ skipping 40 matching lines @@
       # https://codereview.webrtc.org/1552863002/ made its way into chromium.
       cflags += [ "-Wall" ]
     }
   }
 
   if (is_clang) {
     cflags += [
       # Lots of third-party libraries have unused variables. Instead of
       # suppressing them individually, we just blanket suppress them here.
       "-Wno-unused-variable",
+      "-Wno-asm-operand-widths",
     ]
   }
 
   if (is_linux || is_android) {
     cflags_cc += [
       # Don't warn about hash_map in third-party code.
       "-Wno-deprecated",
     ]
   }
 
@@ skipping 350 matching lines @@
 
 if (is_ios || is_mac) {
   # On Mac and iOS, this enables support for ARC (automatic ref-counting).
   # See http://clang.llvm.org/docs/AutomaticReferenceCounting.html.
   config("enable_arc") {
     common_flags = [ "-fobjc-arc" ]
     cflags_objc = common_flags
     cflags_objcc = common_flags
   }
 }