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| author | Lee Nicks <allinux@gmail.com> | 2005-10-28 17:46:09 -0700 |
|---|---|---|
| committer | Paul Mackerras <paulus@samba.org> | 2005-10-29 13:55:19 +1000 |
| commit | 9e3699ea7b8d63eabde7fefa9892e3a258c9c27d (patch) | |
| tree | 66f9318c92f0f88fdf0dc1b2948faec1d429e8a8 /arch/ppc/Makefile | |
| parent | f78541dcec327b0c46b150ee7d727f3db80275c4 (diff) | |
| download | lwn-9e3699ea7b8d63eabde7fefa9892e3a258c9c27d.tar.gz lwn-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/ppc/Makefile')
| -rw-r--r-- | arch/ppc/Makefile | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/arch/ppc/Makefile b/arch/ppc/Makefile index 121d2347b89f..94d5716fa7c3 100644 --- a/arch/ppc/Makefile +++ b/arch/ppc/Makefile @@ -26,6 +26,10 @@ CPPFLAGS += -Iarch/$(ARCH) -Iarch/$(ARCH)/include AFLAGS += -Iarch/$(ARCH) CFLAGS += -Iarch/$(ARCH) -msoft-float -pipe \ -ffixed-r2 -mmultiple + +# No AltiVec instruction when building kernel +CFLAGS += $(call cc-option, -mno-altivec) + CPP = $(CC) -E $(CFLAGS) # Temporary hack until we have migrated to asm-powerpc LINUXINCLUDE += -Iarch/$(ARCH)/include |