linux-kernel - Re: [PATCH v3 2/2] x86_64: Don't save flags on context switch

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Date:	Wed, 1 Oct 2014 11:44:44 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>, X86 ML <x86@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Sebastian Lackner <sebastian@...-team.de>,
	Anish Bhatt <anish@...lsio.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Chuck Ebbert <cebbert.lkml@...il.com>
Subject: Re: [PATCH v3 2/2] x86_64: Don't save flags on context switch

On Wed, Oct 1, 2014 at 11:35 AM, H. Peter Anvin <hpa@...or.com> wrote:
> On 10/01/2014 11:28 AM, Andy Lutomirski wrote:
>>
>>  #define __EXTRA_CLOBBER  \
>>       , "rcx", "rbx", "rdx", "r8", "r9", "r10", "r11", \
>> -       "r12", "r13", "r14", "r15"
>> +       "r12", "r13", "r14", "r15", "flags"
>>
>
> I was under the impression that gcc *always* assumes the flags were
> clobbered for an asm statement.  Otherwise I think we'd have a lot of
> problems.
>

I have no idea, but I doubt that adding the explicit "flags" clobber
hurts, and it will make other people who are unsure about this less
worried.

--Andy

>         -hpa
>
>



-- 
Andy Lutomirski
AMA Capital Management, LLC
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