Re: exit(1) pb

[Adam Heath <adam@lapdoog.doogie.brainfood.com>]

On Tue, 26 Jun 2001, Russell Coker wrote:

> Regarding my problem of exit(1) not causing a program to exit, here's
> some further information:
>
> The following code fragment from src/chat.c in the 2001-06-26 release of
> Portslave seems critical to the exit(1) problem I am having.  The "return
> 0" statement on line 380 of the file seems to change things somehow.  If
> I comment it out then exit(1) will work, if I leave it in then it won't
> work.  In this case *expect != 0 so the return 0 code is not being
>  called!
>
>                 /* Empty expects always succeed. */
>                 if (*expect == 0) {
>                         nsyslog (LOG_DEBUG, "chat_expect - got it");
>                         free(s);
>                         return 0;
>                 }
>
> Here's the difference that this makes to the assembly code that is
> produced:
>
> --- chat.s.works        Tue Jun 26 19:31:48 2001
> +++ chat.s      Tue Jun 26 19:32:38 2001
> @@ -1012,7 +1012,8 @@
>         addl $-12,%esp
>         pushl %esi
>         call free@PLT
> -       addl $32,%esp
> +       xorl %eax,%eax
> +       jmp .L502
>         .p2align 4,,7
>  .L423:
>         addl $-12,%esp

This is stack corruption at its finest.  Some variable being allocated from
the stack in your function is being overrun.

Have fun tracking it down. :)