linux-kernel - Re: Ptrace documentation, draft #1

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Date:	Mon, 16 May 2011 19:48:14 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Denys Vlasenko <vda.linux@...glemail.com>,
	jan.kratochvil@...hat.com, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	indan@....nu
Subject: Re: Ptrace documentation, draft #1

On 05/16, Tejun Heo wrote:
>
> On Mon, May 16, 2011 at 06:53:52PM +0200, Oleg Nesterov wrote:
> > > If you do GETSIGINFO and look at si->si_code, user generated signals
> > > can't have non-zero value there
> >
> > Hmm. The can? sys_kill() sets si_code = 0, but tkill() or queueinfo()
> > can pass any si_code < 0. Also, the kernel can generate the signal
> > with si_code > 0.
>
> Yeah, sure, not non-zero then, but it's still distinguishible, no?

Hmm. Now it is me who is missing context. And probably I misunderstood
the original question:

	Kernel delivers an extra SIGTRAP to tracee after execve syscall
	returns. This is an ordinary signal
	...
	??? can this SIGTRAP be distinguished from "real" user-generated SIGTRAP
	    by looking at its siginfo?

I meant, we can't distinguish this SIGTRAP. But if PTRACE_O_TRACEEXEC is
set then the tracee reports PTRACE_EVENT_EXEC, this is probably
distinguishible. IIUC, si_code > 0 if the tracee reports an event.

Oleg.

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