• David Gibson's avatar
    [PATCH] powerpc: Fix handling of fpscr on 64-bit · 25c8a78b
    David Gibson authored
    The recent merge of fpu.S broken the handling of fpscr for
    ARCH=powerpc and CONFIG_PPC64=y.  FP registers could be corrupted,
    leading to strange random application crashes.
    
    The confusion arises, because the thread_struct has (and requires) a
    64-bit area to save the fpscr, because we use load/store double
    instructions to get it in to/out of the FPU.  However, only the low
    32-bits are actually used, so we want to treat it as a 32-bit quantity
    when manipulating its bits to avoid extra load/stores on 32-bit.  This
    patch replaces the current definition with a structure of two 32-bit
    quantities (pad and val), to clarify things as much as is possible.
    The 'val' field is used when manipulating bits, the structure itself
    is used when obtaining the address for loading/unloading the value
    from the FPU.
    
    While we're at it, consolidate the 4 (!) almost identical versions of
    cvt_fd() and cvt_df() (arch/ppc/kernel/misc.S,
    arch/ppc64/kernel/misc.S, arch/powerpc/kernel/misc_32.S,
    arch/powerpc/kernel/misc_64.S) into a single version in fpu.S.  The
    new version takes a pointer to thread_struct and applies the correct
    offset itself, rather than a pointer to the fpscr field itself, again
    to avoid confusion as to which is the correct field to use.
    
    Finally, this patch makes ARCH=ppc64 also use the consolidated fpu.S
    code, which it previously did not.
    
    Built for G5 (ARCH=ppc64 and ARCH=powerpc), 32-bit powermac (ARCH=ppc
    and ARCH=powerpc) and Walnut (ARCH=ppc, CONFIG_MATH_EMULATION=y).
    Booted on G5 (ARCH=powerpc) and things which previously fell over no
    longer do.
    Signed-off-by: default avatarDavid Gibson <dwg@au1.ibm.com>
    Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
    25c8a78b
Makefile 4.46 KB