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Date: Sun, 15 May 2011 16:28:27 +0200
From: Tejun Heo <tj@kernel.org>
To: Jan Kratochvil <jan.kratochvil@redhat.com>
Cc: oleg@redhat.com, vda.linux@googlemail.com, linux-kernel@vger.kernel.org,
        torvalds@linux-foundation.org, akpm@linux-foundation.org, indan@nul.nu
Subject: Re: getter PTRACE_GETSIGINFO should not modify anything  [Re:
 [PATCH 11/11] ptrace: implement group stop notification for ptracer]
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 <1304869745-1073-12-git-send-email-tj@kernel.org>
 <20110515140232.GB31855@host1.jankratochvil.net>
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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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