From: Borislav Petkov <bp@alien8.de>
To: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86_64: use -mskip-rax-setup when available
Date: Mon, 20 Apr 2015 17:07:35 +0200 [thread overview]
Message-ID: <20150420150735.GA10191@pd.tnic> (raw)
In-Reply-To: <1429532896-10265-1-git-send-email-linux@rasmusvillemoes.dk>
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@rasmusvillemoes.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.
--
next prev parent reply other threads:[~2015-04-20 15:07 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-20 12:28 [PATCH] x86_64: use -mskip-rax-setup when available Rasmus Villemoes
2015-04-20 15:07 ` Borislav Petkov [this message]
2015-04-20 20:24 ` Rasmus Villemoes
2015-04-20 20:41 ` Borislav Petkov
2015-04-23 11:00 ` Rasmus Villemoes
2015-04-23 12:29 ` Borislav Petkov
2015-04-23 12:55 ` Rasmus Villemoes
2015-04-23 13:12 ` Borislav Petkov
2015-04-23 12:55 ` H.J. Lu
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