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

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Message-ID: <20110516172058.GD20624@htj.dyndns.org>
Date:	Mon, 16 May 2011 19:20:58 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
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

Hello,

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?

> > so, if si->si_code contains SIGTRAP | PTRACE_EVENT_* << 8,
> 
> But in this case (without PT_TRACE_EXEC) the tracee simply sends SIGTRAP
> to itself. It will be reported later like a normal signal.

Ah, okay, I missed the context.  I thought we were talking about
GETSIGINFO after traps not the extra SIGTRAP after execve.  Sorry
about that.  :-)

> > Maybe we can remove these if SEIZED?
> 
> Heh... I am not sure.

Yeah, I'm not sure either.  I think the most reasonable solution would
be leaving them alone but strongly discourage their use.

> Hmm. What do you mean? tracehook_report_syscall_exit() can skip
> ptrace_report_syscall() if step, but this is another story. And in this
> case the tracee sends the real signal to itself, unlike
> tracehook_signal_handler() which does ptrace_notify().

Please disregard.  Still was fixated on GETSIGINFO.

Thanks.

-- 
tejun
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