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Message-Id: <1F0B8A18-092F-42AF-91B4-7A5D414ED83D@amacapital.net>
Date: Fri, 20 Oct 2017 18:27:24 +0200
From: Andy Lutomirski <luto@...capital.net>
To: Ingo Molnar <mingo@...nel.org>
Cc: Thomas Garnier <thgarnie@...gle.com>,
Herbert Xu <herbert@...dor.apana.org.au>,
"David S . Miller" <davem@...emloft.net>,
Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
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Subject: Re: [PATCH v1 06/27] x86/entry/64: Adapt assembly for PIE support
> On Oct 20, 2017, at 5:20 PM, Ingo Molnar <mingo@...nel.org> wrote:
>
>
> * Thomas Garnier <thgarnie@...gle.com> wrote:
>
>>>> */
>>>> - cmpq $.Lentry_SYSCALL_64_after_fastpath_call, (%rsp)
>>>> + leaq .Lentry_SYSCALL_64_after_fastpath_call(%rip), %r11
>>>> + cmpq %r11, (%rsp)
>>>> jne 1f
>
>>> This patch seems to add extra overhead to the syscall fast-path even when PIE is
>>> disabled, right?
>>
>> It does add extra instructions when one is not possible, I preferred
>> that over ifdefing but I can change it.
>
> So my problem is, this pattern repeats in many other places as well, but sprinking
> various pieces of assembly code with #ifdefs would be very bad as well.
>
> I have no good idea how to solve this.
>
How about:
.macro JMP_TO_LABEL ...
> Thanks,
>
> Ingo
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