On 10/05, Oleg Nesterov wrote:
>
> On 10/05, Jan Kratochvil wrote:
> >
> > On Mon, 05 Oct 2009 04:51:32 +0200, Oleg Nesterov wrote:
>
> > > It is not trivial to implement, and I don't understand why
> > > it is important to keep this behaviour. But we have the test
> > > case which checks this: attach-into-signal.
> >
> > This testcase is in fact PASSing even when non-SIGSTOP signal is sent as the
> > first one after PTRACE_ATTACH. It has specific handling of such cases.
>
> This test-case also does:
>
> /* detach with SIGPIPE/attach. This should kill tracee */
> ptrace (PTRACE_DETACH, child, (void *) 1, (void *) SIGPIPE);
>
> ptrace (PTRACE_ATTACH, child, (void *) 0, (void *) 0);
>
> waitpid (child, &status, 0);
> assert (WIFSIGNALED (status) && WTERMSIG (status) == SIGPIPE);
>
> It fails if the second PTRACE_ATTACH sees SIGPIPE. This is what
> I can't understand.
Just in case... If I change the test-case
--- a/ptrace-tests/tests/attach-into-signal.c 2009-01-31
13:11:40.000000000 -0800
+++ b/ptrace-tests/tests/attach-into-signal.c 2009-09-20
13:32:30.000000000 -0700
@@ -225,9 +225,9 @@ static void reproduce (void)
return;
}
assert (WIFSTOPPED (status));
- assert (WSTOPSIG (status) == SIGSTOP);
+ assert (WSTOPSIG (status) == SIGPIPE);
/* let tracee run. it must be killed very soon by SIGPIPE */
- ptrace (PTRACE_CONT, child, (void *) 1, (void *) 0);
+ ptrace (PTRACE_CONT, child, (void *) 1, (void *) SIGPIPE);
assert_perror (errno);
pid = waitpid (child, &status, 0);
assert (pid == child);
then it doesn't fail.
> OK. Currently, ptrace(DETACH, SIGXXX) means:
>
> - untrace
>
> - the tracee will get this SIGXXX and handle this signal
>
> - BUT! if the new tracer attaches right now, before the
> tracee handles the signal, this signal will not be
> reported to the new tracer.
>
> With the current utrace-ptrace implementation: if the second
> attach happens before the tracee dequeues SIGXXX, this signal
> will be reported to the new tracer too.
So... Jan, do you think this behaviour change can break gdb?
Oleg.
