Date: Thu, 23 Apr 2009 17:16:33 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Roland McGrath <roland@redhat.com>
Cc: linux-kernel@vger.kernel.org, Jan Kratochvil <jan.kratochvil@redhat.com>,
       Denys Vlasenko <dvlasenk@redhat.com>
Subject: Q: ptrace_signal() && PTRACE_SETSIGINFO (Was: SIGSTOP && ptrace)
Message-ID: <20090423151633.GA3120@redhat.com>
References: <1158166a0904230515h333a78c9uf49931824c1dfe72@mail.gmail.com> <20090423142627.GA31572@redhat.com>
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ptrace_signal:

	signr = current->exit_code;

	/* Update the siginfo structure if the signal has
	   changed.  If the debugger wanted something
	   specific in the siginfo structure then it should
	   have updated *info via PTRACE_SETSIGINFO.  */

Yes. PTRACE_SETSIGINFO can change *info if debugger wants something
special. But then we do:

	if (signr != info->si_signo) {
		info->si_signo = signr;
		info->si_errno = 0;
		info->si_code = SI_USER;
		info->si_pid = task_pid_vnr(current->parent);
		info->si_uid = task_uid(current->parent);
	}

Why? If the tracer changes ->exit_code it should know what it does.
Why do we reset *info?

But the real question, how can PTRACE_SETSIGINFO change ->si_signo
(for example, for do_signal_stop(si_signo)) if this in fact is not
allowed?

Oleg.

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