linux-kernel - Re: [PATCH 13/X] uprobes: introduce UTASK_SSTEP

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Message-ID: <20111025143026.GA12750@redhat.com>
Date:	Tue, 25 Oct 2011 16:30:26 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ananth N Mavinakayanahalli <ananth@...ibm.com>
Cc:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux-mm <linux-mm@...ck.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jonathan Corbet <corbet@....net>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Hugh Dickins <hughd@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...k.frob.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 13/X] uprobes: introduce UTASK_SSTEP_TRAPPED logic

On 10/25, Ananth N Mavinakayanahalli wrote:
>
> No, you are right... my inference was wrong. On a core with a uprobe
> with an explicit raise(SIGABRT) does show the breakpoint.
>
> (gdb) disassemble start_thread2
> Dump of assembler code for function start_thread2:
>    0x0000000000400831 <+0>:	int3
>    0x0000000000400832 <+1>:	mov    %rsp,%rbp
>    0x0000000000400835 <+4>:	sub    $0x10,%rsp
>    0x0000000000400839 <+8>:	mov    %rdi,-0x8(%rbp)
>    0x000000000040083d <+12>:	callq  0x400650 <getpid@plt>
>
> Now, I guess we need to agree on what is the acceptable behavior in the
> uprobes case. What's your suggestion?

Well, personally I think this is acceptable.

Once again, uprobes were designed to be "system wide", and each uprobe
connects to the file. This int3 reflects this fact. In any case, I do
not see how we can hide these int3's. Perhaps we can fool ptrace/core,
but I am not sure this would be really good, this can add more confusion.
And the application itself can read its .text and see int3, what can
we do?

Oleg.

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