linux-kernel - Re: [PATCH 02/10] x86: add support for relative CALL and JMP in alternatives

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Message-ID: <4B7D97A6.4060900@zytor.com>
Date:	Thu, 18 Feb 2010 11:40:22 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Luca Barbieri <luca@...a-barbieri.com>
CC:	mingo@...e.hu, a.p.zijlstra@...llo.nl, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/10] x86: add support for relative CALL and JMP in alternatives

On 02/17/2010 03:42 AM, Luca Barbieri wrote:
> Currently CALL and JMP cannot be used in alternatives because the
> relative offset would be wrong.
> 
> This patch uses the existing x86 instruction parser to parse the
> alternative sequence and fix up the displacements.
> 
> This allows to implement this feature with minimal code.
> 

The existing instruction parser is only present if KPROBES is configured
in... this patch would make it obligatory.  Your patch doesn't reflect
that.  Furthermore, it is ~16K of code and data which probably will make
embedded people unhappy... although perhaps isn't out of line.

A good question, though, is if we actually need support for JMP or CALL
as anything but the first instruction (usually the *only* instruction),
which would make it a lot easier...

	-hpa
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