From 769327258a141ba80ac8b96fce35c68631228370 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Tue, 25 Jun 2024 17:50:04 -0700 Subject: [PATCH] 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 95ece48165c1 ("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 Closes: https://lore.kernel.org/oe-kbuild-all/202406230912.F6XFIyA6-lkp@intel.com/ Fixes: 95ece48165c1 ("locking/atomic/x86: Rewrite x86_32 arch_atomic64_{,fetch}_{and,or,xor}() functions") Link: https://lore.kernel.org/all/202406230912.F6XFIyA6-lkp@intel.com/ Suggested-by: Uros Bizjak Reviewed-and-Tested-by: Uros Bizjak Signed-off-by: Linus Torvalds --- arch/x86/include/asm/cmpxchg_32.h | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-) diff --git a/arch/x86/include/asm/cmpxchg_32.h b/arch/x86/include/asm/cmpxchg_32.h index ed2797f132ce..62cef2113ca7 100644 --- a/arch/x86/include/asm/cmpxchg_32.h +++ b/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)) \