Multiple signals?

Found a problem while debugging gdb.. it looks like we don't correctly handle multiple pending signals in the kernel?

For example, if a task has both a SIGTRAP and a SIGALRM pending, it looks like we only deliver the SIGTRAP but not the SIGALRM. Argh...

Does anybody have an ideas how to debug/fix this? i thought it's just a matter of making intr_do_signal and syscall_do_signal loop back to recheck the SIGPENDING flags, but that doesn't seem to do it....

Test case:
compile the attached program with
gcc -g -o sigstep sigstep.c

then do something like:

(gdb) b handler
Breakpoint 1 at 0x10608: file /home/tausq/gdb/gdb-cvs/gdb/testsuite/gdb.base/sigstep.c, line 31. (gdb) b 66
Breakpoint 2 at 0x106f4: file /home/tausq/gdb/gdb-cvs/gdb/testsuite/gdb.base/sigstep.c, line 66. (gdb) run
Starting program: /home/tausq/gdb/build-cvs/gdb/testsuite/gdb.base/sigstep

Breakpoint 2, main ()
at /home/tausq/gdb/gdb-cvs/gdb/testsuite/gdb.base/sigstep.c:66
66 while (!done);
(gdb) step

Breakpoint 2, main ()
at /home/tausq/gdb/gdb-cvs/gdb/testsuite/gdb.base/sigstep.c:66
66 while (!done);

notice that the printf in the signal handler never gets triggered, and we never stop at the breakpoint on the signal handler....

i wonder if this might also explain some other "lost signals" problems others are seeing?

randolph

Randolph Chung
Debian GNU/Linux Developer, hppa/ia64 ports
http://www.tausq.org/

/* This testcase is part of GDB, the GNU debugger.

Copyright 2004 Free Software Foundation, Inc.

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

*/

#include <stdio.h>
#include <string.h>
#include <signal.h>
#include <sys/time.h>

static volatile int done;

static void
handler (int sig)
{
printf("in handler\n");
done = 1;
} /* handler */

struct itimerval itime;
struct sigaction action;

/* The enum is so that GDB can easily see these macro values. */ enum {
itimer_real = ITIMER_REAL,
itimer_virtual = ITIMER_VIRTUAL
} itimer = ITIMER_VIRTUAL;

main ()
{

  /* Set up the signal handler.  */
  memset (&action, 0, sizeof (action));
  action.sa_handler = handler;
  sigaction (SIGVTALRM, &action, NULL);
  sigaction (SIGALRM, &action, NULL);

/* The values needed for the itimer. This needs to be at least long
enough for the setitimer() call to return. */
memset (&itime, 0, sizeof (itime)); itime.it_value.tv_usec = 250 * 1000;

/* Loop for ever, constantly taking an interrupt. */ while (1)

    {
      /* Set up a one-off timer.  A timer, rather than SIGSEGV, is
	 used as after a timer handler finishes the interrupted code
	 can safely resume.  */
      setitimer (itimer, &itime, NULL);
      /* Wait.  */
      while (!done);
      done = 0;
    }
}

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