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From: Andy Lutomirski <luto@amacapital.net>
Date: Fri, 6 Jun 2014 14:44:51 -0700
Message-ID: <CALCETrXoveOV5qoQ0vBcLiZ15BXAyEiL+oWUWrHKOXuui-Cspg@mail.gmail.com>
Subject: Re: [GIT PULL] x86/vdso changes for v3.16
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: "H. Peter Anvin" <hpa@linux.intel.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Cyrill Gorcunov <gorcunov@openvz.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>, Sasha Levin <sasha.levin@oracle.com>,
        Stefani Seibold <stefani@seibold.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Pavel Emelyanov <xemul@parallels.com>
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Sender: linux-kernel-owner@vger.kernel.org

On Fri, Jun 6, 2014 at 2:42 PM, H. Peter Anvin <hpa@zytor.com> wrote:
> On 06/06/2014 02:39 PM, Andy Lutomirski wrote:
>>>
>>> For accessing memory members doing it via a pointer is pretty much TRT,
>>> but for things that might be in register it is undesirable to force it
>>> out to memory.
>>
>> Do you also believe in the folklore that GCC can optimize code
>> sequences like the things in that header?  Because I'm pretty sure
>> that no clang or gcc version I've ever seen can do it.
>>
>
> I have seen gcc do some pretty sophisticated memory elision lately.
> Don't know if that includes byte swaps.
>
>> On the other hand, even a factor of ten in the time it takes to run
>> vdso2c is completely irrelevant.
>
> Yep, as I noted in the patch I sent (which is broken - updated one
> included here.)

Acked-by: Andy Lutomirski <luto@amacapital.net>

The generated vdso-image-*.c files are identical.

--Andy

>
>         -hpa
>


-- 
Andy Lutomirski
AMA Capital Management, LLC
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