[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..7a21652d58fb361419da5d94e81ba462e4d523fc
--- /dev/null
+++ b/components/cronet/tools/hide_symbols.py
@@ -0,0 +1,88 @@
+#!/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],

[mef, 2017/04/11 21:05:09]

This gets an error in debug simulator build:

ld: scattered reloc r_address too large for architecture i386

[Hiroshi Ichikawa, 2017/04/12 04:35:25]

Does it happen only on trybot, or does it happen on local build too?

For me, it worked fine with local build, and the issue happened only on trybot.

If it's also the case for you, one possible workaround is to stop integrating
hide_symbols.py into the BUILD.gn file, and run the script manually locally to
build the static library. It's not a great solution, though.

Another possible solution is to upgrade the version of XCode toolchain in
trybot. I'm doubting that the issue happens only with an old version of XCode
toolchain, though not verified.

[mef, 2017/04/12 15:57:50]

It happens locally, but only for one configuration - x86 Debug. 
Possibly because of extra debug symbols that make object file too big?  
I'm thinking about reducing symbol level and/or splitting combined .o file into
two or more. 
Not that great either.
I'm using XCode 8.2.1, which (IIUIC) is current.

+    '-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
+  ]
+  subprocess.check_call(command)
+
+  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()