Re: truss issue

[CC'ed Bruce]

Maxim Konovalov wrote on Mon, Dec 15, 2003 at 03:35:31PM +0300: 
> Hello,
> 
> On Mon, 16 Jun 2003, 23:40+0900, Alexander Nedotsukov wrote:
> 
> > All,
> >
> > I found current truss behaviour a bit strange. It coredumps always if
> > trussed process do without any significant reason for my understanding.
> > I also confused with comment for commit originally introduced this
> > functionality
> > http://www.freebsd.org/cgi/cvsweb.cgi/src/usr.bin/truss/main.c.diff?r1=1.9&r2=1.10.
> > I propose patch attached to make truss always return result of trussed
> > process and do not kill() itself. What do you think about it?
> 
> As a matter of fact, bin/58970 is a backout of rev.1.10 truss/main.c:
> 
> ----------------------------
> revision 1.10
> date: 1998/08/24 10:17:20;  author: cracauer;  state: Exp;  lines: +9 -1
> When exiting on SIGINT, exit with signal status
> =============================================================================
> 
> But a code does not match the comment and does something funny:
> 
> _at__at_ -216,6 +217,7 _at__at_
>         break;
>        case S_SIG:
>         fprintf(outfile, "SIGNAL %lu\n", pfs.val);
> +       sigexit = pfs.val;
>         break;
>        case S_EXIT:
>         fprintf (outfile, "process exit, rval = %lu\n", pfs.val);
> _at__at_ -232,5 +234,11 _at__at_
>      if (ioctl(Procfd, PIOCCONT, val) == -1)
>        warn("PIOCCONT");
>    } while (pfs.why != S_EXIT);
> +  if (sigexit) {
> +    if (sigexit == SIGQUIT)
> +      exit(sigexit);
> +    (void) signal(sigexit, SIG_DFL);
> +    (void) kill(getpid(), sigexit);
> +  }
>    return 0;
>  }
> 
> Gentlemen, does anobody know what is going on there?

If you catch a signal like SIGINT or SIGTERM (as opposed to leaving
the original OS handler to handle it), then you need to reissue that
same signal to yourself when after your did whatever cleanup you
want. 

The general reason is that the parent of the process needs to be
informed that you exited on a signal.

The specific reason is that if you don't, then a shellscript will not
be interruptable with SIGINT or SIGTERM.

I have a lengthly web page about it at 
  http://www.cons.org/cracauer/sigint.html


As for for problem with the coredumps, I assume this is when SIGQUIT
is used? The proper way of handling this would be to change truss (and
other transparent wrappers) to ulimit the coredump size to zero and
then reissue the SIGQUIT signal.

But the integrety towards the parent needs to be maintained, you must
not exit without a signal exit status or you get runaway scripts.

Martin
-- 
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Martin Cracauer <cracauer_at_cons.org>   http://www.cons.org/cracauer/
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