Workaround removal of __system_property_get in Android NDK.

base/sys_info_android.cc

Index: base/sys_info_android.cc
diff --git a/base/sys_info_android.cc b/base/sys_info_android.cc
index 92eefef6527b0ad29a44be05663e1bf7a9b02442..ae02447ab640b3defe341af58e7e228858657080 100644
--- a/base/sys_info_android.cc
+++ b/base/sys_info_android.cc
@@ -4,6 +4,7 @@
 
 #include "base/sys_info.h"
 
+#include <dlfcn.h>
 #include <sys/system_properties.h>
 
 #include "base/android/sys_utils.h"
@@ -14,6 +15,33 @@
 #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