linux-kernel - [PATCH] Use -mskip-rax-setup if supported

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Message-ID: <CAMe9rOrfDo3MGaQc_s5crw3TrYhS8NtqeyRcUFiA0yAV8e9Nig@mail.gmail.com>
Date:	Thu, 16 Apr 2015 14:23:44 -0700
From:	"H.J. Lu" <hjl.tools@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>
Subject: [PATCH] Use -mskip-rax-setup if supported

GCC 5 added a compiler option, -mskip-rax-setup, for x86-64.  It skips
setting up the RAX register when SSE is disabled and there are no
variable arguments passed in vector registers.  Since kernel doesn't
pass vector registers to functions with variable arguments, this option
can be used to optimize the x86-64 kernel.  For kernel 3.17:

    text   data    bss    dec      hex   filename
11455921 2204048 5853184 19513153 129bf41 vmlinux #with -mskip-rax-setup
11480079 2204048 5853184 19537311 12a1d9f vmlinux

-- 
H.J.

View attachment "0001-Use-mskip-rax-setup-if-supported.patch" of type "text/x-patch" (1401 bytes)