From owner-freebsd-current  Wed Mar 12  8:25:49 2003
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Date: Thu, 13 Mar 2003 03:25:41 +1100 (EST)
From: Bruce Evans <bde@zeta.org.au>
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To: Tim Robbins <tjr@FreeBSD.ORG>
Cc: current@FreeBSD.ORG
Subject: Re: failed to set signal flags properly for ast()
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On Wed, 12 Mar 2003, Tim Robbins wrote:

> Compile, run under gdb, then type "print test()" when the program receives
> SIGABRT. Seems to work incorrectly on 4.7 too.
>
> #include <stdio.h>
> #include <stdlib.h>
>
> void
> test(void)
> {
>
> 	puts("hello");
> }
>
> int
> main(int argc, char *argv[])
> {
>
> 	abort();
> 	exit(0);
> }

Thanks.  At last it is possible to reproduce this bug :-).

The bug seems to be that issignal() is quite broken.  It gets called
for masked signals in the P_TRACED case, but never does anything for
masked signals, but at least the following things poing to a need
for doing something for masked signals:
- the special case for P_TRACED in SIGPENDING()
- the incorrect behaviour of the above program in RELENG_4.  I think
  it misbehaves in the same way under -current except in the INVARIANTS
  case the sanity check spews kernel printfs.
- code in NetBSD's issignal() to do something in the (p->p_stat == SSTOP)
  case without even checking if there are any signals (masked or not).

This bug seems to go back to at least FreeBSD-1 (Net/2).

SIGPENDING() is also inconsistent with issignal() in the P_PPWAIT case.
I think this just wastes time doing null calls to issignal(), and
triggers the INVARIANTS check in the same way as the P_TRACED case
(see below).  This seems to go back to FreeBSD-1 too.

SIGPENDING() is consistent with issignal() in the S_SIG case, but this
may be wrong since S_SIG is similar to P_TRACED.

The invariants check gets trigger as follows:
- sigpending() is called correctly.
- ast() clears the flags set by sigpending() and "handles" the signal
  using "while ((sig == cursig(td)) != 0) postsig()".  But cursig()
  doesn't find any signals since all the pending ones are masked.
- userret() checks that pending signals were handled.  It finds
  unhandled masked ones and thinks they needed handling because
  P_TRACED is set.
(IIRC, there is only a SIGTRAP pending to begin with, but attempting
to control the process using ^C^Z gave masked SIGINTs and SIGSTOPs
too).

Appart from the diagnostic, the incorrect working in -current is to
loop endlessly calling ast() and usrret().  ^C^Z doesn't stop it
because they are masked.

Bruce

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