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    Subject[PATCH 2.6.14-rc1] 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.
    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)
    -
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