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

commit 2400fd822f467cb4c886c879d8ad99feac9cf319 upstream.

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: 859deea949c3 ("[POWERPC] Cell timebase bug workaround")
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>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index 578e5a0d116d01be48d6fd240146dacd38976a09..b3b9d089dda6c1bbf042b89ff8a33c364c00b66f 100644 (file)
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -1054,7 +1054,9 @@
                                "       .llong 0\n"                     \
                                "       .llong 0\n"                     \
                                ".previous"                             \
-                       : "=r" (rval) : "i" (CPU_FTR_CELL_TB_BUG)); rval;})
+                       : "=r" (rval) \
+                       : "i" (CPU_FTR_CELL_TB_BUG) : "cr0"); \
+                       rval;})
 #else
 #define mftb()         ({unsigned long rval;   \
                        asm volatile("mftb %0" : "=r" (rval)); rval;})