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

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Message-ID: <20111025060059.GA8247@in.ibm.com>
Date:	Tue, 25 Oct 2011 11:31:00 +0530
From:	Ananth N Mavinakayanahalli <ananth@...ibm.com>
To:	Oleg Nesterov <oleg@...hat.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 Mon, Oct 24, 2011 at 06:13:06PM +0200, Oleg Nesterov wrote:
> On 10/24, Ananth N Mavinakayanahalli wrote:
> >
> > Thinking further on this, in the normal 'running gdb on a core' case, we
> > won't have this problem, as the binary that we point gdb to, will be a
> > pristine one, without the uprobe int3s, right?
> 
> Not sure I understand.
> 
> I meant, if we have a binary with uprobes (iow, register_uprobe() installed
> uprobes into that file), then gdb will see int3's with or without the core.
> Or you can add uprobe into glibc, say you can probe getpid(). Now (again,
> with or without the core) disassemble shows that getpid() starts with int3.
> 
> But I guess you meant something else...

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?

Ananth

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