• Lee Nicks's avatar
    [PATCH] ppc: prevent GCC 4 from generating AltiVec instructions in kernel · 9e3699ea
    Lee Nicks authored
    
    
    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: default avatarLee Nicks <allinux@gmail.com>
    Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
    Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
    9e3699ea