From: Lee Nicks 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 Cc: Paul Mackerras Cc: Benjamin Herrenschmidt Signed-off-by: Andrew Morton --- arch/ppc/Makefile | 4 ++++ arch/ppc64/Makefile | 3 +++ 2 files changed, 7 insertions(+) diff -puN arch/ppc64/Makefile~ppc-prevent-gcc-4-from-generating-altivec-instructions-in-kernel arch/ppc64/Makefile --- devel/arch/ppc64/Makefile~ppc-prevent-gcc-4-from-generating-altivec-instructions-in-kernel 2005-09-14 00:08:13.000000000 -0700 +++ devel-akpm/arch/ppc64/Makefile 2005-09-14 00:08:38.000000000 -0700 @@ -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 += $(call cc-option,-funit-at-a-time) diff -puN arch/ppc/Makefile~ppc-prevent-gcc-4-from-generating-altivec-instructions-in-kernel arch/ppc/Makefile --- devel/arch/ppc/Makefile~ppc-prevent-gcc-4-from-generating-altivec-instructions-in-kernel 2005-09-14 00:08:13.000000000 -0700 +++ devel-akpm/arch/ppc/Makefile 2005-09-14 00:09:00.000000000 -0700 @@ -26,6 +26,10 @@ CPPFLAGS += -Iarch/$(ARCH) -Iarch/$(ARCH AFLAGS += -Iarch/$(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 _