https://github.com/torvalds/linux
Revision bdbc29c19b2633b1d9c52638fb732bcde7a2031a authored by Paul Mackerras on 27 August 2013, 06:07:49 UTC, committed by Benjamin Herrenschmidt on 27 August 2013, 06:59:30 UTC
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: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
1 parent f5f6cbb
Tip revision: bdbc29c19b2633b1d9c52638fb732bcde7a2031a authored by Paul Mackerras on 27 August 2013, 06:07:49 UTC
powerpc: Work around gcc miscompilation of __pa() on 64-bit
powerpc: Work around gcc miscompilation of __pa() on 64-bit
Tip revision: bdbc29c
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