Re: how can I get a backtrace from inside my program?

[jcupitt gmail com]

2008/10/31 Brian J. Tarricone <bjt23 cornell edu>:
> Garth's KidStuff wrote:
> > I have a large Gtk app running on Ubuntu and I'd love to be able to log
> > stack trace information when unusual events occur.  Any ideas on where to
> > look for this?
>
> If you don't mind that it only works on Linux, with glibc and gcc, take a
> look at backtrace() and backtrace_symbols() (or backtrace_symbols_fd()).
>  I've never used it myself, but that might be what you're looking for.

Another option (brace yourself, this is very hacky) is to start gdb,
attach to yourself, send a "bt" (backtrace) command, and capture the
output. It's slow, but it does work, sort of, and it would be slightly
more portable.

Of course your app will need to be built with -g, the user will need
to have gdb installed, and the ugly way I've done it in this scrap of
code is horribly insecure. You'd need to trim the output down a bit
too.

-----------
#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>

/* Largest output we can capture.
*/
#define MAX_TRACE (1024)

char *
getstacktrace( const char *argv0 )
{
      pid_t pid = getpid();
      char output[MAX_TRACE];
      char cmd[256];
      FILE *fp;
      int i;
      int ch;

      snprintf( cmd, 256,
              "echo bt > /tmp/poop | gdb -batch %s %d -x /tmp/poop",
              argv0, pid );
      if( !(fp = popen( cmd, "r" )) )
              return( NULL );

      for( i = 0; i < MAX_TRACE - 1 && (ch = fgetc( fp )) != EOF; i++ )
              output[i] = ch;
      output[i] = 0;

      pclose( fp );

      return( strdup( output ) );
}

int
main( int argc, char **argv )
{
      char *trace;

      if( (trace = getstacktrace( argv[0] )) ) {
              printf( "stack trace:\n%s", trace );
              free( trace );
      }

      return( 0 );
}
--------------

J