• Paul Mackerras's avatar
    powerpc: Work around gcc miscompilation of __pa() on 64-bit · bdbc29c1
    Paul Mackerras authored
    On 64-bit, __pa(&static_var) gets miscompiled by recent versions of
    gcc as something like:
    
            addis 3,2,.LANCHOR1+4611686018427387904@toc@ha
            addi 3,3,.LANCHOR1+4611686018427387904@toc@l
    
    This ends up effectively ignoring the offset, since its bottom 32 bits
    are zero, and means that the result of __pa() still has 0xC in the top
    nibble.  This happens with gcc 4.8.1, at least.
    
    To work around this, for 64-bit we make __pa() use an AND operator,
    and for symmetry, we make __va() use an OR operator.  Using an AND
    operator rather than a subtraction ends up with slightly shorter code
    since it can be done with a single clrldi instruction, whereas it
    takes three instructions to form the constant (-PAGE_OFFSET) and add
    it on.  (Note that MEMORY_START is always 0 on 64-bit.)
    
    CC: <stable@vger.kernel.org>
    Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
    Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
    bdbc29c1
page.h 11.9 KB