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Message-ID: <20080425203717.GB25950@Krystal>
Date: Fri, 25 Apr 2008 16:37:17 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To: "H. Peter Anvin" <hpa@...or.com>
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
* H. Peter Anvin (hpa@...or.com) wrote:
> Mathieu Desnoyers wrote:
>> This epilogue should then be used on both branches of the condition,
>> like this :
>> if (unlikely(imv_cond(var))) {
>> imv_cond_end();
>> ...
>> } else {
>> imv_cond_end();
>> ...
>> }
>> Where imv_cond_end() would look like this :
>> +/*
>> + * Puts a test and branch make sure the %al register and ZF are not live
>> + * anymore.
>> + * All asm statements clobbers the flags, but add "cc" clobber just to be
>> sure.
>> + * Clobbers %al.
>> + */
>> +#define imv_cond_end() \
>> + do { \
>> + asm (".section __imv_cond_end,\"a\",@progbits\n\t" \
>> + _ASM_PTR "1f\n\t" \
>> + ".previous\n\t" \
>> + "1:\n\t" \
>> + : : : "a", "cc"); \
>> + } while (0)
>> +
>
> 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.
Mathieu
> -hpa
--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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