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")
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>
Signed-off-by: Willy Tarreau <w@1wt.eu>

diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index 469d7715d6aaf9caa0bcc91a16b2e96583f1ea8c..954168be78788e009de4a65c419cb8e4782400cf 100644 (file)
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -1136,7 +1136,7 @@
                                "       .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;})