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

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Message-ID: <481241DC.3070601@zytor.com>
Date:	Fri, 25 Apr 2008 13:41:00 -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:
>>> +
>> As far as this is concerned, all you accomplish here is that gcc, if it 
>> wants to re-use the %al value, will copy it into another register before 
>> doing your imv_conv_end().
>>
> 
> Exactly, and by doing so, it will have to add instructions (mov, push..)
> in the instruction pattern I am looking for and therefore I will detect
> this and fall back on standard immediate values.
> 

So what you're saying is you'll follow all the branches of code until 
you detect an immediate value (and eflags) kill.

Yes, that should work.  It's still ugly, and I have to say I find the 
complexity rather distasteful.  I am willing to be convinced it's worth 
it, but I would really like to see hard numbers.

Personally, I wouldn't be all that surprised if you lost more in 
constraining gcc scheduling than you gain.

	-hpa
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