[Cronet] Build static libcronet.a for iOS with complete dependencies.

components/cronet/tools/hide_symbols.py

Index: components/cronet/tools/hide_symbols.py
diff --git a/components/cronet/tools/hide_symbols.py b/components/cronet/tools/hide_symbols.py
new file mode 100755
index 0000000000000000000000000000000000000000..55e7fb81c2bab1d8042c197c09c9daca0091acb7
--- /dev/null
+++ b/components/cronet/tools/hide_symbols.py
@@ -0,0 +1,101 @@
+#!/usr/bin/env python
+
+# Copyright 2017 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.
+
+# Create a static library which exposes only symbols which are explicitly marked
+# as visible e.g., by __attribute__((visibility("default"))).
+#
+# See BUILD.gn in this directory for usage example.
+#
+# This way, we can reduce risk of symbol conflict when linking it into apps
+# by exposing internal symbols, especially in third-party libraries.
+
+import optparse
+import os
+import subprocess
+
+
+# Mapping from GN's target_cpu attribute to ld's -arch parameter.
+# Taken from the definition of config("compiler") in:
+#   //build/config/mac/BUILD.gn
+GN_CPU_TO_LD_ARCH = {
+  'x64': 'x86_64',
+  'x86': 'i386',
+  'armv7': 'armv7',
+  'arm': 'armv7',
+  'arm64': 'arm64',
+}
+
+
+def main():
+  parser = optparse.OptionParser()
+  parser.add_option(
+      '--input_libs',
+      help='Comma-separated paths to input .a files which contain symbols '
+           'which must be always linked.')
+  parser.add_option(
+      '--deps_lib',
+      help='The path to a complete static library (.a file) which contains all '
+           'dependencies of --input_libs. .o files in this library are also '
+           'added to the output library, but only if they are referred from '
+           '--input_libs.')
+  parser.add_option(
+      '--output_obj',
+      help='Outputs the generated .o file here. This is an intermediate file.')
+  parser.add_option(
+      '--output_lib',
+      help='Outputs the generated .a file here.')
+  parser.add_option(
+      '--current_cpu',
+      help='The current processor architecture in the format of the target_cpu '
+           'attribute in GN.')
+  (options, args) = parser.parse_args()
+  assert not args
+
+  # ld -r concatenates multiple .o files and .a files into a single .o file,
+  # while "hiding" symbols not marked as visible.
+  command = [
+    'xcrun', 'ld',
+    '-arch', GN_CPU_TO_LD_ARCH[options.current_cpu],
+    '-r',
+  ]
+  for input_lib in options.input_libs.split(','):
+    # By default, ld only pulls .o files out of a static library if needed to
+    # resolve some symbol reference. We apply -force_load option to input_lib
+    # (but not to deps_lib) to force pulling all .o files.
+    command += ['-force_load', input_lib]
+  command += [
+    options.deps_lib,
+    '-o', options.output_obj
+  ]
+  try:
+    subprocess.check_call(command)
+  except subprocess.CalledProcessError:
+    # Work around LD failure for x86 Debug buiilds when it fails with error:
+    # ld: scattered reloc r_address too large for architecture i386
+    if options.current_cpu == "x86":
+      # Combmine input lib with dependencies into output lib.
+      command = [
+        'xcrun', 'libtool', '-static', '-no_warning_for_no_symbols',
+        '-o', options.output_lib,
+        options.input_libs, options.deps_lib,
+      ]
+      subprocess.check_call(command)
+      return
+
+  if os.path.exists(options.output_lib):
+    os.remove(options.output_lib)
+
+  # Creates a .a file which contains a single .o file.
+  command = [
+    'xcrun', 'ar', '-r',
+    options.output_lib,
+    options.output_obj,
+  ]
+  subprocess.check_call(command)
+
+
+if __name__ == "__main__":
+  main()