linux-kernel - Re: getter PTRACE_GETSIGINFO should not modify anything [Re: [PATCH 11/11] ptrace: implement group stop notification for ptracer]

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Message-ID: <20110515142827.GF23665@htj.dyndns.org>
Date:	Sun, 15 May 2011 16:28:27 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Jan Kratochvil <jan.kratochvil@...hat.com>
Cc:	oleg@...hat.com, vda.linux@...glemail.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, indan@....nu
Subject: Re: getter PTRACE_GETSIGINFO should not modify anything  [Re:
 [PATCH 11/11] ptrace: implement group stop notification for ptracer]

Hello, Jan.

On Sun, May 15, 2011 at 04:02:32PM +0200, Jan Kratochvil wrote:
> Or there should be some other way how to query the siginfo_t state
> fully transparently (*).
>
> (*) But if there exists such syscall it probably does not make sense to modify
>     anything by PTRACE_GETSIGINFO.

If there's a syscall which doesn't affect notification state, then we
need something which does clear it.  Either way, I suppose you're
saying we need both something which clears the notification and
something which doesn't.

> Imagine various LD_PRELOAD tools which try to wrap system/library calls and
> operate with ptrace while keeping it transparent for the original debugger.
> (I have a bunch of such libraries for testing gdb/strace/etc. written there.)
> 
> Also complicated debuggers with internal OO hierarchy would need to just wrap
> PTRACE_GETSIGINFO into an internal function to make it transparent for calls
> not intending to modify the debuggee state.

We can add a flag or new request for that but I don't know.  Those are
pretty fringe use cases and they don't even strictly require such
feature - Even for LD_PRELOAD, it can simply keep scheduling INTERRUPT
until the application calls the wrapped GETSIGINFO when it detects the
stopped state has changed.  It can be easily done from userland.

Thank you.

-- 
tejun
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