arm: Add thumb target and associated fixes

build/common.gypi

 # Copyright (c) 2009 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   'variables': {
     # .gyp files should set chromium_code to 1 if they build Chromium-specific
@@ skipping 182 matching lines @@
     # Set to select the Title Case versions of strings in GRD files.
     'use_titlecase_in_grd_files%': 0,
 
     # Used to disable Native Client at compile time, for platforms where it
     # isn't supported
     'disable_nacl%': 0,
 
     # Set ARM-v7 compilation flags
     'armv7%': 0,
 
+    # Set Thumb compilation flags.
+    'arm_thumb%': 0,
+
     'conditions': [
       ['OS=="linux"', {
         # This will set gcc_version to XY if you are running gcc X.Y.*.
         # This is used to tweak build flags for gcc 4.4.
         'gcc_version%': '<!(python <(DEPTH)/build/compiler_version.py)',
         'conditions': [
           ['branding=="Chrome" or linux_chromium_breakpad==1', {
             'linux_breakpad%': 1,
           }, {
             'linux_breakpad%': 0,
@@ skipping 490 matching lines @@
               }],
             ],
             'cflags': [
               '-m32',
             ],
             'ldflags': [
               '-m32',
             ],
           }],
           ['target_arch=="arm"', {
-            'conditions': [
-              ['armv7==1', {
-                'target_conditions': [
-                  ['_toolset=="target"', {
+            'target_conditions': [
+              ['_toolset=="target"', {
+                'cflags_cc': [
+                  # The codesourcery arm-2009q3 toolchain warns at that the ABI
+                  # has changed whenever it encounters a varargs function. This
+                  # silences those warnings, as they are not helpful and
+                  # clutter legitimate warnings.
+                  '-Wno-abi',
+                ],
+                'conditions': [
+                  ['arm_thumb == 1', {
+                    'cflags': [
+                    '-mthumb',
+                    # TODO(piman): -Wa,-mimplicit-it=thumb is needed for
+                    # inline assembly that uses condition codes but it's
+                    # suboptimal. Better would be to #ifdef __thumb__ at the
+                    # right place and have a separate thumb path.
+                    '-Wa,-mimplicit-it=thumb',
+                    ]
+                  }],
+                  ['armv7==1', {
                     'cflags': [
                       '-march=armv7-a',
                       '-mtune=cortex-a8',
                       '-mfpu=neon',
                       '-mfloat-abi=softfp',
                     ],
                   }],
                 ],
               }],
             ],
@@ skipping 310 matching lines @@
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }
 
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