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powerpc/asm: Mark cr0 as clobbered in mftb() 

The workaround for the CELL timebase bug does not correctly mark cr0 as
being clobbered. This means GCC doesn't know that the asm block changes cr0 and
might leave the result of an unrelated comparison in cr0 across the block, which
we then trash, leading to basically random behaviour.

Fixes: 859deea949 ("[POWERPC] Cell timebase bug workaround")
Cc: stable@vger.kernel.org # v2.6.19+
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
[mpe: Tweak change log and flag for stable]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Oliver O'Halloran 2017-07-06 18:46:43 +10:00 committed by Michael Ellerman
parent 41d0c2ecde
commit 2400fd822f
1 changed files with 1 additions and 1 deletions
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arch/powerpc/include/asm/reg.h
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@ -1303,7 +1303,7 @@ static inline void msr_check_and_clear(unsigned long bits)
" .llong 0\n" \
".previous" \
: "=r" (rval) \
: "i" (CPU_FTR_CELL_TB_BUG), "i" (SPRN_TBRL)); \
: "i" (CPU_FTR_CELL_TB_BUG), "i" (SPRN_TBRL) : "cr0"); \
rval;})
#else
#define mftb() ({unsigned long rval; \