Search "__android_log_" for *.h and *.c* in gecko and you will find more than 400 matches. When some module wants to output a log message on b2g, normally it will do: #ifdef MOZ_WIDGET_GONK #include <android/log.h> #endif and then #ifdef MOZ_WIDGET_GONK __android_log_write(ANDROID_LOG_INFO, SOME_TAG, cstr); #endif The good part of doing this is: * The log will surely be seen in android logcat. * Android log API has severity and tag, allowing the log viewer to filter log messages. The bad part of it is: * We litter throughout our code base with the above code snippets, probably because of copy and paste. * The log messages are only available on emulator and device. B2G desktop won't see the messages. Some alternatives to __android_log_print/write() calls: 1. printf_stderr() 2. PR_LOG() 3. just printf() and redirect stdout and stderr to some self-pipe. Then we can decide where to output these messages.

Dupe to bug 881389, which tracks the work to unify logging in b2g.