android: Hide JNI exports by default.

build/common.gypi

 # Copyright (c) 2012 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 expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 1778 matching lines @@
 
         # Uses system APIs for decoding audio and video.
         'use_libffmpeg%': '0',
 
         # TODO(torne): Remove this unsupported option once all the places that
         # test it have been updated.
         'use_system_stlport%': 0,
 
         # Copy it out one scope.
         'android_webview_build%': '<(android_webview_build)',
-
-        # Default android linker script for shared library exports.
-        'android_linker_script%': '<(SHARED_INTERMEDIATE_DIR)/android_exports.lst',
       }],  # OS=="android"
       ['embedded==1', {
         'use_system_fontconfig%': 0,
       }, {
         'use_system_fontconfig%': 1,
       }],
       ['chromecast==1', {
         'enable_mpeg2ts_stream_parser%': 1,
         'ffmpeg_branding%': 'ChromeOS',
         'ozone_platform_ozonex%': 1,
@@ skipping 652 matching lines @@
         # pnacl uses the clang compiler so we need to suppress all the
         # same warnings as we do for clang.
         # TODO(sbc): Remove these if/when they are removed from the clang
         # build.
         '-Wno-unused-function',
         '-Wno-char-subscripts',
         '-Wno-c++11-extensions',
         '-Wno-unnamed-type-template-args',
       ],
 
+      # By default, Android targets have their exported JNI symbols stripped,
+      # so we test the manual JNI registration code paths that are required
+      # when using the crazy linker. To allow use of native JNI exports (lazily

[rmcilroy, 2015/02/03 13:43:56]

nit - maybe mention that binaries which set "use_chromium_linker=1" use the
crazy linker to make it obvious what gyp variables would affect this.

+      # resolved by the JVM), targets can enable this variable, which will stop
+      # the stripping from happening. Only targets which do not need to be
+      # compatible with the crazy linker are permitted to set this.
+      'use_native_jni_exports%': 0,
+
       'conditions': [
         ['OS=="win" and component=="shared_library"', {
           # See http://msdn.microsoft.com/en-us/library/aa652367.aspx
           'win_release_RuntimeLibrary%': '2', # 2 = /MD (nondebug DLL)
           'win_debug_RuntimeLibrary%': '3',   # 3 = /MDd (debug DLL)
         }, {
           # See http://msdn.microsoft.com/en-us/library/aa652367.aspx
           'win_release_RuntimeLibrary%': '0', # 0 = /MT (nondebug static)
           'win_debug_RuntimeLibrary%': '1',   # 1 = /MTd (debug static)
         }],
@@ skipping 2098 matching lines @@
               '_STLP_USE_PTR_SPECIALIZATIONS=1',
               'CHROME_BUILD_ID="<(chrome_build_id)"',
             ],
             'ldflags!': [
               '-pthread',  # Not supported by Android toolchain.
             ],
             'ldflags': [
               '-Wl,--no-undefined',
             ],
             'conditions': [
-              ['component=="static_library"', {
+              ['component=="static_library" and android_webview_build==0', {
                 'ldflags': [
                   '-Wl,--exclude-libs=ALL',
                 ],
+                'target_conditions': [
+                  ['use_native_jni_exports==0', {
+                    # Use a linker version script to strip JNI exports from
+                    # binaries which have not specifically asked to use them.
+                    'ldflags': [
+                      '-Wl,--version-script=<!(cd <(DEPTH) && pwd -P)/build/android/android_no_jni_exports.lst',
+                    ],
+                  }],
+                ],
               }],
               ['clang==1', {
                 'cflags': [
                   # Work around incompatibilities between bionic and clang
                   # headers.
                   '-D__compiler_offsetof=__builtin_offsetof',
                   '-Dnan=__builtin_nan',
                 ],
                 'conditions': [
                   ['target_arch=="arm"', {
@@ skipping 1255 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }