linux-kernel - Re: [PATCH 06/18] x86/asm/64: Use pop instead of movq in syscall_return_via

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Date:   Fri, 27 Oct 2017 22:11:05 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     X86 ML <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 06/18] x86/asm/64: Use pop instead of movq in
 syscall_return_via_sysret

On Thu, Oct 26, 2017 at 01:26:38AM -0700, Andy Lutomirski wrote:
> Saves 64 bytes.
> 
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
>  arch/x86/entry/entry_64.S | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index d6404a613df4..9dafafa3e0ec 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -313,10 +313,18 @@ return_from_SYSCALL_64:
>  	 */
>  syscall_return_via_sysret:
>  	/* rcx and r11 are already restored (see code above) */
> -	RESTORE_EXTRA_REGS
> -	RESTORE_C_REGS_EXCEPT_RCX_R11
> -	movq	RSP(%rsp), %rsp
>  	UNWIND_HINT_EMPTY
> +	POP_EXTRA_REGS
> +	popq	%rsi	/* skip r11 */
> +	popq	%r10
> +	popq	%r9
> +	popq	%r8
> +	popq	%rax
> +	popq	%rsi	/* skip rcx */
> +	popq	%rdx
> +	popq	%rsi
> +	popq	%rdi
> +	movq	RSP-ORIG_RAX(%rsp), %rsp
>  	USERGS_SYSRET64
>  END(entry_SYSCALL_64)
>  
> -- 

Reviewed-by: Borislav Petkov <bp@...e.de>

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--