linux-kernel - Re: [PATCH] x86: use register variable to get stack pointer value

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Message-ID: <20170929153828.rtxwllhsjgiaeaos@treble>
Date:   Fri, 29 Sep 2017 10:38:28 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: use register variable to get stack pointer value

On Fri, Sep 29, 2017 at 05:15:36PM +0300, Andrey Ryabinin wrote:
> Currently we use current_stack_pointer() function to get the value
> of the stack pointer register. Since commit f5caf621ee35
> ("x86/asm: Fix inline asm call constraints for Clang") we have stack
> register variable declared. It can be used instead of current_stack_pointer()
> function which allows to optimize away some excessive "mov %rsp, %<dst>"
> instructions:
> 
> -mov    %rsp,%rdx
> -sub    %rdx,%rax
> -cmp    $0x3fff,%rax
> -ja     ffffffff810722fd <ist_begin_non_atomic+0x2d>
> 
> +sub    %rsp,%rax
> +cmp    $0x3fff,%rax
> +ja     ffffffff810722fa <ist_begin_non_atomic+0x2a>
> 
> Remove current_stack_pointer(), rename __asm_call_sp to current_stack_pointer
> and use it instead of removed function.
> 
> Signed-off-by: Andrey Ryabinin <aryabinin@...tuozzo.com>

Reviewed-by: Josh Poimboeuf <jpoimboe@...hat.com>

-- 
Josh