x86-32: fix cmpxchg8b_emu build error with clang

The kernel test robot reported that clang no longer compiles the 32-bit
x86 kernel in some configurations due to commit 95ece48
("locking/atomic/x86: Rewrite x86_32 arch_atomic64_{,fetch}_{and,or,xor}()
functions").

The build fails with

  arch/x86/include/asm/cmpxchg_32.h:149:9: error: inline assembly requires more registers than available

and the reason seems to be that not only does the cmpxchg8b instruction
need four fixed registers (EDX:EAX and ECX:EBX), with the emulation
fallback the inline asm also wants a fifth fixed register for the
address (it uses %esi for that, but that's just a software convention
with cmpxchg8b_emu).

Avoiding using another pointer input to the asm (and just forcing it to
use the "0(%esi)" addressing that we end up requiring for the sw
fallback) seems to fix the issue.

Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
Fixes: 95ece48 ("locking/atomic/x86: Rewrite x86_32 arch_atomic64_{,fetch}_{and,or,xor}() functions")
Link: https://lore.kernel.org/all/[email protected]/
Suggested-by: Uros Bizjak <[email protected]>
Reviewed-and-Tested-by: Uros Bizjak <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: torvalds

arch/x86/include/asm/cmpxchg_32.h

@@ -93,10 +93,9 @@ static __always_inline bool __try_cmpxchg64_local(volatile u64 *ptr, u64 *oldp,
 									\
 	asm volatile(ALTERNATIVE(_lock_loc				\
 				 "call cmpxchg8b_emu",			\
-				 _lock "cmpxchg8b %[ptr]", X86_FEATURE_CX8) \
-		     : [ptr] "+m" (*(_ptr)),				\
-		       "+a" (o.low), "+d" (o.high)			\
-		     : "b" (n.low), "c" (n.high), "S" (_ptr)		\
+				 _lock "cmpxchg8b %a[ptr]", X86_FEATURE_CX8) \
+		     : "+a" (o.low), "+d" (o.high)			\
+		     : "b" (n.low), "c" (n.high), [ptr] "S" (_ptr)	\
 		     : "memory");					\
 									\
 	o.full;								\
@@ -122,12 +121,11 @@ static __always_inline u64 arch_cmpxchg64_local(volatile u64 *ptr, u64 old, u64
 									\
 	asm volatile(ALTERNATIVE(_lock_loc				\
 				 "call cmpxchg8b_emu",			\
-				 _lock "cmpxchg8b %[ptr]", X86_FEATURE_CX8) \
+				 _lock "cmpxchg8b %a[ptr]", X86_FEATURE_CX8) \
 		     CC_SET(e)						\
 		     : CC_OUT(e) (ret),					\
-		       [ptr] "+m" (*(_ptr)),				\
 		       "+a" (o.low), "+d" (o.high)			\
-		     : "b" (n.low), "c" (n.high), "S" (_ptr)		\
+		     : "b" (n.low), "c" (n.high), [ptr] "S" (_ptr)	\
 		     : "memory");					\
 									\
 	if (unlikely(!ret))						\