diff options
author | Lee Nicks <allinux@gmail.com> | 2005-10-28 20:46:09 -0400 |
---|---|---|
committer | Paul Mackerras <paulus@samba.org> | 2005-10-28 23:55:19 -0400 |
commit | 9e3699ea7b8d63eabde7fefa9892e3a258c9c27d (patch) | |
tree | 66f9318c92f0f88fdf0dc1b2948faec1d429e8a8 /arch/ppc | |
parent | f78541dcec327b0c46b150ee7d727f3db80275c4 (diff) |
[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')
-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 | |||
26 | AFLAGS += -Iarch/$(ARCH) | 26 | AFLAGS += -Iarch/$(ARCH) |
27 | CFLAGS += -Iarch/$(ARCH) -msoft-float -pipe \ | 27 | CFLAGS += -Iarch/$(ARCH) -msoft-float -pipe \ |
28 | -ffixed-r2 -mmultiple | 28 | -ffixed-r2 -mmultiple |
29 | |||
30 | # No AltiVec instruction when building kernel | ||
31 | CFLAGS += $(call cc-option, -mno-altivec) | ||
32 | |||
29 | CPP = $(CC) -E $(CFLAGS) | 33 | CPP = $(CC) -E $(CFLAGS) |
30 | # Temporary hack until we have migrated to asm-powerpc | 34 | # Temporary hack until we have migrated to asm-powerpc |
31 | LINUXINCLUDE += -Iarch/$(ARCH)/include | 35 | LINUXINCLUDE += -Iarch/$(ARCH)/include |