linux-kernel - Re: [PATCH 5/7] uprobes/x86: Gather "riprel" functions together

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Date:	Thu, 3 Apr 2014 21:50:14 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Jim Keniston <jkenisto@...ux.vnet.ibm.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	David Long <dave.long@...aro.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Jonathan Lebon <jlebon@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/7] uprobes/x86: Gather "riprel" functions together

On 04/02, Jim Keniston wrote:
>
> On Mon, 2014-03-31 at 21:44 +0200, Oleg Nesterov wrote:
> ...
> > +static void
> > +handle_riprel_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs, long *correction)
> > +{
> > +	if (auprobe->fixups & (UPROBE_FIX_RIP_AX | UPROBE_FIX_RIP_CX)) {
> > +		struct arch_uprobe_task *autask;
> > +
> > +		autask = &current->utask->autask;
> > +		if (auprobe->fixups & UPROBE_FIX_RIP_AX)
> > +			regs->ax = autask->saved_scratch_register;
> > +		else
> > +			regs->cx = autask->saved_scratch_register;
> > +
> > +		/*
> > +		 * The original instruction includes a displacement, and so
> > +		 * is 4 bytes longer than what we've just single-stepped.
> > +		 * Fall through to handle stuff like "jmpq *...(%rip)" and
> > +		 * "callq *...(%rip)".
> > +		 */
> > +		if (correction)
> > +			*correction += 4;
> > +	}
> > +}
>
> This is another case of a glitch in the code being moved.  Since this
> code was moved to its own function, the "Fall through" comment makes no
> sense.  Maybe
> 		 * Caller may need to apply other fixups to handle stuff
> 		 * like "jmpq *...(%rip)" and "callq *...(%rip)".

Thanks. updated the comment in v2.

Oleg.

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