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| author | Paul Mackerras <paulus@samba.org> | 2013-08-27 06:07:49 (GMT) |
|---|---|---|
| committer | Benjamin Herrenschmidt <benh@kernel.crashing.org> | 2013-08-27 06:59:30 (GMT) |
| commit | bdbc29c19b2633b1d9c52638fb732bcde7a2031a (patch) | |
| tree | de4fe4de7dc8abe6d79db9e99dd042c1e34cec56 /arch/powerpc/Kconfig | |
| parent | f5f6cbb61610b7bf9d9d96db9c3979d62a424bab (diff) | |
| download | linux-bdbc29c19b2633b1d9c52638fb732bcde7a2031a.tar.xz | |
powerpc: Work around gcc miscompilation of __pa() on 64-bit
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>
Diffstat (limited to 'arch/powerpc/Kconfig')
| -rw-r--r-- | arch/powerpc/Kconfig | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig index dbd9d3c..9cf59816d 100644 --- a/arch/powerpc/Kconfig +++ b/arch/powerpc/Kconfig @@ -979,6 +979,7 @@ config RELOCATABLE must live at a different physical address than the primary kernel. +# This value must have zeroes in the bottom 60 bits otherwise lots will break config PAGE_OFFSET hex default "0xc000000000000000" |