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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>,
 "H . Peter Anvin" <hpa@...or.com>, Peter Zijlstra <peterz@...radead.org>,
 Josh Poimboeuf <jpoimboe@...hat.com>, Arnd Bergmann <arnd@...db.de>,
 Kees Cook <keescook@...omium.org>,
 Andrey Ryabinin <aryabinin@...tuozzo.com>,
 Matthias Kaehlcke <mka@...omium.org>,
 Tom Lendacky <thomas.lendacky@....com>, Andy Lutomirski <luto@...nel.org>,
 "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
 Borislav Petkov <bp@...e.de>, "Rafael J . Wysocki" <rjw@...ysocki.net>,
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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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