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

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Date:	Wed, 02 Apr 2014 12:53:15 -0700
From:	Jim Keniston <jkenisto@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.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 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)".

Jim

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