linux-ext4 - Re: [PATCH 1/1] x86: fix text

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Message-ID: <481209F2.4050908@zytor.com>
Date:	Fri, 25 Apr 2008 09:42:26 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	Andi Kleen <andi@...stfloor.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Jiri Slaby <jirislaby@...il.com>,
	David Miller <davem@...emloft.net>, zdenek.kabelac@...il.com,
	rjw@...k.pl, paulmck@...ux.vnet.ibm.com, akpm@...ux-foundation.org,
	linux-ext4@...r.kernel.org, herbert@...dor.apana.org.au,
	penberg@...helsinki.fi, clameter@....com,
	linux-kernel@...r.kernel.org, pageexec@...email.hu,
	Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [PATCH 1/1] x86: fix text_poke

Mathieu Desnoyers wrote:
> 
> Yes, the immediate values, in general, only need to do atomic writes,
> because I have taken care of placing the mov instruction in the correct
> alignment so its immediate value happens to be aligned in memory.
> However, the latest optimisation I did to change a conditional branch
> into a jump when the correct code pattern is detected :
> 
> mov, test, bne short
> into a
> nop2, nop2, nop1, jmp short
> 
> or
> 
> mov, test, bne near
> into a
> nop2, nop2, nop1, jmp near
> 

And how, pray tell, do you deal with the fact that:

a) the EFLAGS may be live on exit;
b) there might be a jump into the middle of this instruction sequence?

	-hpa
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