From: Lee Nicks Date: Sat, 29 Oct 2005 00:46:09 +0000 (-0700) Subject: [PATCH] ppc: prevent GCC 4 from generating AltiVec instructions in kernel X-Git-Tag: v2.6.15-rc1~59^2~57 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9e3699ea7b8d63eabde7fefa9892e3a258c9c27d;p=linux-2.6 [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 Cc: Benjamin Herrenschmidt Signed-off-by: Andrew Morton Signed-off-by: Paul Mackerras --- diff --git a/arch/ppc/Makefile b/arch/ppc/Makefile index 121d2347b8..94d5716fa7 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 diff --git a/arch/ppc64/Makefile b/arch/ppc64/Makefile index 743f0dbdeb..db1b25cdb5 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)