Allow for __system_property_get() being hidden in Android 'L' and bey…

…ond.

src/time_zone_info.cc

@@ -649,22 +649,22 @@ std::unique_ptr<ZoneInfoSource> FileZoneInfoSource::Open(
   return std::unique_ptr<ZoneInfoSource>(new FileZoneInfoSource(fp, length));
 }
 
-#if defined(__BIONIC__)
-class BionicZoneInfoSource : public FileZoneInfoSource {
+#if defined(__ANDROID__)
+class AndroidZoneInfoSource : public FileZoneInfoSource {
  public:
   static std::unique_ptr<ZoneInfoSource> Open(const std::string& name);
 
  private:
-  explicit BionicZoneInfoSource(FILE* fp, std::size_t len)
+  explicit AndroidZoneInfoSource(FILE* fp, std::size_t len)
       : FileZoneInfoSource(fp, len) {}
 };
 
-std::unique_ptr<ZoneInfoSource> BionicZoneInfoSource::Open(
+std::unique_ptr<ZoneInfoSource> AndroidZoneInfoSource::Open(
     const std::string& name) {
   // Use of the "file:" prefix is intended for testing purposes only.
   if (name.compare(0, 5, "file:") == 0) return Open(name.substr(5));
 
-  // See Bionic libc/tzcode/bionic.cpp for additional information.
+  // See Android's libc/tzcode/bionic.cpp for additional information.
   for (const char* tzdata : {"/data/misc/zoneinfo/current/tzdata",
                              "/system/usr/share/zoneinfo/tzdata"}) {
     std::unique_ptr<FILE, int (*)(FILE*)> fp(FOpen(tzdata, "rb"), fclose);
@@ -692,7 +692,7 @@ std::unique_ptr<ZoneInfoSource> BionicZoneInfoSource::Open(
       ebuf[40] = '\0';  // ensure zone name is NUL terminated
       if (strcmp(name.c_str(), ebuf) == 0) {
         if (fseek(fp.get(), static_cast<long>(start), SEEK_SET) != 0) break;
-        return std::unique_ptr<ZoneInfoSource>(new BionicZoneInfoSource(
+        return std::unique_ptr<ZoneInfoSource>(new AndroidZoneInfoSource(
             fp.release(), static_cast<std::size_t>(length)));
       }
     }
@@ -717,8 +717,8 @@ bool TimeZoneInfo::Load(const std::string& name) {
   auto zip = cctz_extension::zone_info_source_factory(
       name, [](const std::string& name) -> std::unique_ptr<ZoneInfoSource> {
         if (auto zip = FileZoneInfoSource::Open(name)) return zip;
-#if defined(__BIONIC__)
-        if (auto zip = BionicZoneInfoSource::Open(name)) return zip;
+#if defined(__ANDROID__)
+        if (auto zip = AndroidZoneInfoSource::Open(name)) return zip;
 #endif
         return nullptr;
       });

src/time_zone_lookup.cc

@@ -14,8 +14,11 @@
 
 #include "cctz/time_zone.h"
 
-#if defined(__BIONIC__)
+#if defined(__ANDROID__)
 #include <sys/system_properties.h>
+#if __ANDROID_API__ >= 21
+#include <dlfcn.h>
+#endif
 #endif
 #include <cstdlib>
 #include <cstring>
@@ -26,6 +29,35 @@
 
 namespace cctz {
 
+#if defined(__ANDROID__) && __ANDROID_API__ >= 21
+namespace {
+// Android 'L' removes __system_property_get() from the NDK, however
+// it is still a hidden symbol in libc so we use dlsym() to access it.
+// See Chromium's base/sys_info_android.cc for a similar example.
+
+using property_get_func = int (*)(const char*, char*);
+
+property_get_func LoadSystemPropertyGet() {
+  int flag = RTLD_LAZY | RTLD_GLOBAL;
+#if defined(RTLD_NOLOAD)
+  flag |= RTLD_NOLOAD;  // libc.so should already be resident
+#endif
+  if (void* handle = dlopen("libc.so", flag)) {
+    void* sym = dlsym(handle, "__system_property_get");
+    dlclose(handle);
+    return reinterpret_cast<property_get_func>(sym);
+  }
+  return nullptr;
+}
+
+int __system_property_get(const char* name, char* value) {
+  static property_get_func system_property_get = LoadSystemPropertyGet();
+  return system_property_get ? system_property_get(name, value) : -1;
+}
+
+}  // namespace
+#endif
+
 std::string time_zone::name() const {
   return time_zone::Impl::get(*this).name();
 }
@@ -67,7 +99,7 @@ time_zone local_time_zone() {
 #else
   tz_env = std::getenv("TZ");
 #endif
-#if defined(__BIONIC__)
+#if defined(__ANDROID__)
   char sysprop[PROP_VALUE_MAX];
   if (tz_env == nullptr)
     if (__system_property_get("persist.sys.timezone", sysprop) > 0)