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| author | Lee Nicks <allinux@gmail.com> | 2005-10-29 02:46:09 +0200 |
|---|---|---|
| committer | Paul Mackerras <paulus@samba.org> | 2005-10-29 05:55:19 +0200 |
| commit | 9e3699ea7b8d63eabde7fefa9892e3a258c9c27d (patch) | |
| tree | 66f9318c92f0f88fdf0dc1b2948faec1d429e8a8 /arch/ppc64 | |
| parent | powerpc: Merge xmon (diff) | |
| download | linux-9e3699ea7b8d63eabde7fefa9892e3a258c9c27d.tar.xz linux-9e3699ea7b8d63eabde7fefa9892e3a258c9c27d.zip | |
[PATCH] ppc: prevent GCC 4 from generating AltiVec instructions in kernel
Depending on how GCC is built, GCC 4 may generate altivec instructions without
user explicitly requesting vector operations in the code. Although this is a
performance booster for user applications, it is a problem for kernel.
This patch explicitly instruct GCC to NOT generate altivec instructions while
building the kernel.
Here are some test cases I ran.
(1) build gcc 4.0.1 with '--with-cpu=7450 --enable-altivec
--enable-cxx-flags=-mcpu=7450', and use this gcc to build kernel WITHOUT
this kernel patch. Kernel fail to boot up on a 7450 board because of
altivec instructions in kernel.
(2) build gcc 4.0.1 with "--with-cpu=7450 --enable-altivec
--enable-cxx-flags=-mcpu=7450", and use this gcc to build kernel WITH this
kernel patch. Kernel boot up on a 7450 board without any problem.
(3) build gcc 4.0.1 with "--with-cpu=750 --enable-cxx-flags=-mcpu=750",
and use this gcc to build kernel with or without this kernel patch.
Kernel boot up on a 7450 board without any problem.
This patch should also work with GCC 3 or even earlier GCC 2.95.3.
Signed-off-by: Lee Nicks <allinux@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Diffstat (limited to 'arch/ppc64')
| -rw-r--r-- | arch/ppc64/Makefile | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/arch/ppc64/Makefile b/arch/ppc64/Makefile index 743f0dbdebf3..db1b25cdb5be 100644 --- a/arch/ppc64/Makefile +++ b/arch/ppc64/Makefile @@ -75,6 +75,9 @@ else CFLAGS += $(call cc-option,-mtune=power4) endif +# No AltiVec instruction when building kernel +CFLAGS += $(call cc-option, -mno-altivec) + # Enable unit-at-a-time mode when possible. It shrinks the # kernel considerably. CFLAGS += $(call cc-option,-funit-at-a-time) |