linux-kernel - Re: [PATCH] x86_64: use -mskip-rax-setup when available

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Date:	Mon, 20 Apr 2015 17:07:35 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86_64: use -mskip-rax-setup when available

On Mon, Apr 20, 2015 at 02:28:16PM +0200, Rasmus Villemoes wrote:
> gcc 5 supports the option -mskip-rax-setup to avoid emitting the
> two-byte instruction xor %eax,%eax before a vararg function
> call. Clearing %eax is redundant in the kernel, since no callee
> expects any floating point arguments, and hence never use the incoming
> value of %eax for anything.
> 
> For a defconfig kernel, the .text saving is around 26 kB:
> 
> $ size /tmp/vmlinux.{old,new}
>    text    data     bss     dec     hex filename
> 12221850        1735352 1077248 15034450         e56852 /tmp/vmlinux.old
> 12195955        1735352 1077248 15008555         e5032b /tmp/vmlinux.new
> 
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
> ---
> 
> Nothing seems to have happened on the kernel side since H.J. Lu
> implemented this in December.  Since gcc 5 is officially released

I see the same patch from him from Apr. 16th:

https://lkml.kernel.org/r/CAMe9rOrfDo3MGaQc_s5crw3TrYhS8NtqeyRcUFiA0yAV8e9Nig@mail.gmail.com

Why are you sending it too?

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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