Messages in this thread Patch in this message | | | Date | Tue, 13 Sep 2005 23:12:06 -0700 | From | Lee Nicks <> | Subject | [PATCH 2.6.14-rc1] ppc: prevent GCC 4 from generating AltiVec instructions in kernel |
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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. Please review and apply it.
Signed-off-by: Lee Nicks <allinux@gmail.com> ======================================
diff -ruN linux-2.6.14-rc1-original/arch/ppc/Makefile linux-2.6.14-rc1/arch/ppc/Makefile --- linux-2.6.14-rc1-original/arch/ppc/Makefile 2005-09-13 20:00:34.000000000 -0700 +++ linux-2.6.14-rc1/arch/ppc/Makefile 2005-09-13 20:09:36.000000000 -0700 @@ -26,6 +26,12 @@ AFLAGS += -Iarch/$(ARCH) CFLAGS += -Iarch/$(ARCH) -msoft-float -pipe \ -ffixed-r2 -mmultiple + +# No AltiVec instruction when building kernel +ifeq ($(call cc-option-yn, -mno-altivec), y) +CFLAGS += -mno-altivec +endif + CPP = $(CC) -E $(CFLAGS) # Temporary hack until we have migrated to asm-powerpc LINUXINCLUDE += -Iarch/$(ARCH)/include diff -ruN linux-2.6.14-rc1-original/arch/ppc64/Makefile linux-2.6.14-rc1/arch/ppc64/Makefile --- linux-2.6.14-rc1-original/arch/ppc64/Makefile 2005-09-13 20:00:36.000000000 -0700 +++ linux-2.6.14-rc1/arch/ppc64/Makefile 2005-09-13 20:08:41.000000000 -0700 @@ -75,6 +75,11 @@ CFLAGS += $(call cc-option,-mtune=power4) endif
+# No AltiVec instruction when building kernel +ifeq ($(call cc-option-yn, -mno-altivec), y) +CFLAGS += -mno-altivec +endif + # Enable unit-at-a-time mode when possible. It shrinks the # kernel considerably. CFLAGS += $(call cc-option,-funit-at-a-time) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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