From 769327258a141ba80ac8b96fce35c68631228370 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@linux-foundation.org>
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 <lkp@intel.com>
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 <ubizjak@gmail.com>
Reviewed-and-Tested-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
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 ed2797f132ce0..62cef2113ca74 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)) \
--
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