Add gyp machinery to build with packed ARM relative relocations.

build/android/gyp/pack_arm_relocations.py

Index: build/android/gyp/pack_arm_relocations.py
diff --git a/build/android/gyp/pack_arm_relocations.py b/build/android/gyp/pack_arm_relocations.py
new file mode 100755
index 0000000000000000000000000000000000000000..f117ad7b80805bd619e5d5d5f55cd9e44266e13d
--- /dev/null
+++ b/build/android/gyp/pack_arm_relocations.py
@@ -0,0 +1,110 @@
+#!/usr/bin/env python
+#
+# 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.
+
+"""Pack ARM relative relocations in a library (or copy unchanged).
+
+If --enable-packing, invoke the relocation_packer tool to pack the .rel.dyn
+section in the given library files.  This step is inserted after the libraries
+are stripped.  Packing adds a new .android.rel.dyn section to the file and
+reduces the size of .rel.dyn accordingly.
+
+Currently packing only understands ARM32 shared libraries.  For all other
+architectures --enable-packing should be set to zero.  In this case the
+script copies files verbatim, with no attempt to pack relative relocations.
+
+Any library listed in --exclude-packing-list is also copied verbatim,
+irrespective of any --enable-packing setting.  Typically this would be
+'libchromium_android_linker.so'.
+"""
+
+import json
+import optparse
+import os
+import shlex
+import shutil
+import sys
+import tempfile
+
+from util import build_utils
+
+def PackArmLibraryRelocations(android_pack_relocations,
+                              android_objcopy,
+                              library_path,
+                              output_path):
+  if not build_utils.IsTimeStale(output_path, [library_path]):
+    return
+
+  # Copy and add a 'NULL' .android.rel.dyn section for the packing tool.
+  with tempfile.NamedTemporaryFile() as stream:
+    stream.write('NULL')
+    stream.flush()
+    objcopy_command = [android_objcopy,
+                       '--add-section', '.android.rel.dyn=%s' % stream.name,
+                       library_path, output_path]
+    build_utils.CheckOutput(objcopy_command)
+
+  # Pack R_ARM_RELATIVE relocations.
+  pack_command = [android_pack_relocations, output_path]
+  build_utils.CheckOutput(pack_command)
+
+
+def CopyArmLibraryUnchanged(library_path, output_path):
+  if not build_utils.IsTimeStale(output_path, [library_path]):
+    return
+
+  shutil.copy(library_path, output_path)
+
+
+def main():
+  parser = optparse.OptionParser()
+
+  parser.add_option('--enable-packing',
+      choices=['0', '1'],
+      help='Pack relocations if 1, otherwise plain file copy')
+  parser.add_option('--exclude-packing-list',
+      default='',
+      help='Names of any libraries explicitly not packed')
+  parser.add_option('--android-pack-relocations',
+      help='Path to the ARM relocations packer binary')
+  parser.add_option('--android-objcopy',
+      help='Path to the toolchain\'s objcopy binary')
+  parser.add_option('--stripped-libraries-dir',
+      help='Directory for stripped libraries')
+  parser.add_option('--packed-libraries-dir',
+      help='Directory for packed libraries')
+  parser.add_option('--libraries-file',
+      help='Path to json file containing list of libraries')
+  parser.add_option('--stamp', help='Path to touch on success')
+
+  options, _ = parser.parse_args()
+  enable_packing = options.enable_packing == '1'
+  exclude_packing_set = set(shlex.split(options.exclude_packing_list))
+
+  with open(options.libraries_file, 'r') as libfile:
+    libraries = json.load(libfile)
+
+  build_utils.MakeDirectory(options.packed_libraries_dir)
+
+  for library in libraries:
+    library_path = os.path.join(options.stripped_libraries_dir, library)
+    output_path = os.path.join(options.packed_libraries_dir, library)
+
+    if enable_packing and library not in exclude_packing_set:
+      PackArmLibraryRelocations(options.android_pack_relocations,
+                                options.android_objcopy,
+                                library_path,
+                                output_path)
+    else:
+      CopyArmLibraryUnchanged(library_path, output_path)
+
+  if options.stamp:
+    build_utils.Touch(options.stamp)
+
+  return 0
+
+
+if __name__ == '__main__':
+  sys.exit(main())