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

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Date:	Sun, 15 May 2011 16:02:32 +0200
From:	Jan Kratochvil <jan.kratochvil@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	oleg@...hat.com, vda.linux@...glemail.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, indan@....nu
Subject: getter PTRACE_GETSIGINFO should not modify anything  [Re: [PATCH
 11/11] ptrace: implement group stop notification for ptracer]

On Sun, 08 May 2011 17:49:05 +0200, Tejun Heo wrote:
> which triggers INTERRUPT trap but is sticky until the next
> PTRACE_GETSIGINFO.

PTRACE_GETSIGINFO is a getter.  It must not modify anything.  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.

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.

Thanks,
Jan
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