How to get longer stack dump (tombstone) from android?

Question

As I have noticed, logcat returns always 34 lines of crashlog, like this:

4cf7c700  401c0000 
4cf7c704  48463ff0 
4cf7c708  44d11f7c  
4cf7c70c  afd0cd89 
4         


        

Answer 1

The crash handling program in android, which is called debuggerd, only writes a portion of the stack into the log, but writes the full stack into the tombstone file. This is hardcoded in system/core/debuggerd/debuggerd.c.

Look in the routine debug_stack_and_code() for the calls to _LOG(). The second parameter to _LOG controls whether stuff goes only to the tombstone, or to the log and the tombstone.

Where you see (sp_depth>2||only_in_tombstone), you can change the 2 to something else to get deeper stack frames reported in the log. This assumes that you can re-compile debuggerd and replace it on your system. If not, you're stuck with examining the tombstone files themselves for the longer stack dumps.

The dumps are created by debuggerd when a program crashes under Linux. When this happens, the kernel will send a signal to the dying program. This signal is caught by a special signal handler installed in every native Android app. by the bionic C library. The signal handler contacts debuggerd (via a named pipe), which then connects back to the dying program using ptrace to read registers and memory to produce the tombstone and log entries.