Workaround removal of __system_property_get in Android NDK.

base/sys_info_android.cc

 // 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.
 
 #include "base/sys_info.h"
 
+#include <dlfcn.h>
 #include <sys/system_properties.h>
 
 #include "base/android/sys_utils.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_piece.h"
 #include "base/strings/stringprintf.h"
 #include "base/sys_info_internal.h"
 
+// TODO(rmcilroy): Update API level when 'L' gets an official API level.
+#if (__ANDROID_API__ >= 9999 /* 'L' */)
+
+// Android 'L' removes __system_property_get from the NDK, however it is still
+// a hidden symbol in libc. Until we remove all calls of __system_property_get
+// from Chrome we work around this by defining a weak stub here, which uses
+// dlsym to but ensures that Chrome uses the real system
+// implementatation when loaded.
+int __system_property_get(const char* name, char* value) {
+  static int (*__real_system_property_get)(const char*, char*) = NULL;

[Nico, 2014/07/17 16:55:50]

Is this always called from the same thread? (I think we build with
-fno-threadsafe-statics.)

[rmcilroy, 2014/07/17 18:41:51]

Good point.  Updated to use a LazyInstance instead.

+  if (__real_system_property_get == NULL) {
+    // libc.so should already be open, get a handle to it.
+    void* handle = dlopen("libc.so", RTLD_NOLOAD);
+    if (!handle) {
+      LOG(FATAL) << "Cannot dlopen libc.so: " << dlerror();
+    }
+    __real_system_property_get = reinterpret_cast<int (*)(const char*, char*)>(
+        dlsym(handle, "__system_property_get"));
+    if (!__real_system_property_get) {
+      LOG(FATAL) << "Cannot resolve __system_property_get(): " << dlerror();
+    }
+  }
+  return (*__real_system_property_get)(name, value);
+}
+
+#endif
+
 namespace {
 
 // Default version of Android to fall back to when actual version numbers
 // cannot be acquired. Use the latest Android release with a higher bug fix
 // version to avoid unnecessarily comparison errors with the latest release.
 // This should be manually kept up-to-date on each Android release.
 const int kDefaultAndroidMajorVersion = 4;
 const int kDefaultAndroidMinorVersion = 4;
 const int kDefaultAndroidBugfixVersion = 99;
 
@@ skipping 143 matching lines @@
     base::internal::LazySysInfoValue<bool,
         android::SysUtils::IsLowEndDeviceFromJni> >::Leaky
     g_lazy_low_end_device = LAZY_INSTANCE_INITIALIZER;
 
 bool SysInfo::IsLowEndDevice() {
   return g_lazy_low_end_device.Get().value();
 }
 
 
 }  // namespace base