[PING][PATCH] Segfault while unwinding an invalid function pointer

[Pete Eberlein]

Jakub Jelinek wrote on 10/29/2007 03:41:53 PM:
>> This should only happen for a signal frame or a garbage address.
> 
> Or a function without unwind info.  Something that happens quite often.
> E.g. even with -fasynchronous-unwind-tables built glibc, the outermost
> stack frame is always without unwind info and so every backtrace(3)
> will hit your tmpfile/write/fclose at least once.  This is too costly.

Would a single call to tmpfile be acceptable for the duration of the 
program?  I'm thinking something like this:

   static FILE* tmp_file = NULL;
   static int tmp_offset = 0;

   if (!tmp_file) {
     tmp_file = tmpfile();
   }
   if (tmp_file)
     {
       if (tmp_offset + len > 4096)
         {
	  rewind(tmp_file);
	  tmp_offset = 0;
	}
       rc = write (fileno(tmp_file), addr, len);
       tmp_offset += rc;
       result = (rc == len);
     }

This way tmp_file is only called once, write is called each time, and 
rewind is called when the file would exceed 4k.

Is this still too costly?  Or should I stop asking?

-- 
Pete Eberlein
IBM Linux Technology Center
Linux on Power Toolchain