linux-kernel - Re: [PATCH v7 3.2-rc2 8/30] x86: analyze instruction and determine fixups.

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Message-ID: <20111201055211.GD18380@linux.vnet.ibm.com>
Date:	Thu, 1 Dec 2011 11:22:11 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-mm <linux-mm@...ck.org>, Ingo Molnar <mingo@...e.hu>,
	Andi Kleen <andi@...stfloor.org>,
	Christoph Hellwig <hch@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Roland McGrath <roland@...k.frob.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Anton Arapov <anton@...hat.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Stephen Wilson <wilsons@...rt.ca>
Subject: Re: [PATCH v7 3.2-rc2 8/30] x86: analyze instruction and determine
 fixups.

* Oleg Nesterov <oleg@...hat.com> [2011-11-30 19:57:51]:

> On 11/18, Srikar Dronamraju wrote:
> >
> > +static void handle_riprel_insn(struct mm_struct *mm, struct uprobe *uprobe,
> > +							struct insn *insn)
> > +{
> > [...snip...]
> > +	if (insn->immediate.nbytes) {
> > +		cursor++;
> > +		memmove(cursor, cursor + insn->displacement.nbytes,
> > +						insn->immediate.nbytes);
> > +	}
> > +	return;
> > +}
> 
> Of course I don not understand this code. But it seems that it can
> rewrite uprobe->insn ?
> 

Yes, we do rewrite the instruction for the RIP relative instructions. 
But the first byte is still intact.

> If yes, don't we need to save the original insn for unregister_uprobe?

When we unregister, we just put back the least opcode size which
happens to be the first byte for x86.

-- 
Thanks and Regards
Srikar

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