# Re: Just-in-time debugging on Linux

# Re: Just-in-time debugging on Linux

[Michael Veksler]

/References/: <007a01c20e82$daf93e20$0301a8c0@rowboat 
<http://sources.redhat.com/ml/gdb/2002-06/msg00063.html>> 
<20020608172614.GA16912@redhat.com 
<http://sources.redhat.com/ml/gdb/2002-06/msg00064.html>>

 > Christopher,
 >
 > > On windows you'd do:
 > >
 > > set cygwin=error_start=x:/path/to/gdb.exe
 >
 > Thanks lots, but I meant Linux. Does anyone know the trick to launch gdb
 > automatically there?
 >
 > Robin

Try the following code:

#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
#include <signal.h>
#include <stdio.h>

static char* exec_name="";

static void crash_handler(int sig)
{
   int status=0;
   int pid;
   char * gdb_array[]={"gdb", exec_name, "PID", NULL};
   char pid_str[40];

   sprintf(pid_str, "%d%c", getpid(), '\0');
   gdb_array[2]= pid_str;

   pid= fork();

   if (pid < 0)    /* error */
     abort();
   else if (pid)   /* parent */
   {
     sleep(60);   /* Give GDB time to attach */
     _exit(1);     /* you can skip this line by telling gdb to "return" */
   }
   else            /* child */
     execvp("gdb", gdb_array);
}
void register_gdb()
{
   signal(SIGQUIT, crash_handler);  /* Normally got from Ctrl-\ */
   signal(SIGILL,  crash_handler);
   signal(SIGTRAP, crash_handler);
   signal(SIGABRT, crash_handler);
   signal(SIGFPE,  crash_handler);
   signal(SIGBUS,  crash_handler);
   signal(SIGSEGV, crash_handler);  /* This is the most common crash */
   signal(SIGSYS,  crash_handler);
}

void crash_segv()
{
   int *p=0;
   *p=1;
}

int main(int argc, char *argv[])
{
   exec_name=argv[0];
   register_gdb();
   crash_segv();
   return 0;
}

Re: Just-in-time debugging on Linux

[Robin Rowe]

Michael,

>    signal(SIGSEGV, crash_handler);  /* This is the most common crash */

This is an interesting approach, but I want to trap unmodified programs.

Thanks,

Robin
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Re: Just-in-time debugging on Linux

[phi]

Robin Rowe wrote:
> 
> Michael,
> 
> >    signal(SIGSEGV, crash_handler);  /* This is the most common crash */
> 
> This is an interesting approach, but I want to trap unmodified programs.
> 


Then wrap them up in a script 

rename prog xyz into xyz.ori  this doesn't modify the prog?

then implement the script xyz that does

xyz::
#! your shell
gdb xyz.ori $@

and have you gdbinit (or other ways) to catch the signal you want.

At xyz invocation we start gdb wich start xyz.ori wich will catch the signal
and let you see.


==================

If you really don't want to rename xyz.ori then have the script xyz earlier in
your PATH and make the script invoke the xyz from its original path

Phi

Re: Just-in-time debugging on Linux

[Tom Tromey]

>>>>> "phi" == phi  <phi@hpfrcu81.france.hp.com> writes:

phi> Then wrap them up in a script 
phi> rename prog xyz into xyz.ori  this doesn't modify the prog?
phi> then implement the script xyz that does

phi> xyz::
phi> #! your shell
phi> gdb xyz.ori $@

This doesn't really work.  One problem is that the inferior won't
start running automatically.  The other problem is that I/O
redirections get hosed (I think).

I do think this would be a useful feature for gdb.  I've wanted it for
a number of years now, but haven't had the time to implement it.

Incidentally your script is missing a `--args'.

Tom

Just-in-time debugging

[Robin Rowe]

Hi. Can I configure gdb so that it will launch automatically in response to
a core dump?

Thanks,

Robin
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Re: Just-in-time debugging

[Christopher Faylor]

On Fri, Jun 07, 2002 at 05:24:29PM -0700, Robin Rowe wrote:
>Hi. Can I configure gdb so that it will launch automatically in response to
>a core dump?

On what system?  On windows you'd do:

set cygwin=error_start=x:/path/to/gdb.exe

I don't know if it's possible to do on unix or not.

cgf

Re: Just-in-time debugging on Linux

[Robin Rowe]

Christopher,

> On windows you'd do:
>
> set cygwin=error_start=x:/path/to/gdb.exe

Thanks lots, but I meant Linux. Does anyone know the trick to launch gdb
automatically there?

Robin
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