linux-kernel - [PATCH] m68k: Fix asm register constraints for atomic ops

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Message-Id: <20210725104618.365790-1-geert@linux-m68k.org>
Date:   Sun, 25 Jul 2021 12:46:18 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Greg Ungerer <gerg@...inux.org>, Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Boqun Feng <boqun.feng@...il.com>
Cc:     Brendan Jackman <jackmanb@...gle.com>,
        kernel test robot <lkp@...el.com>,
        Arnd Bergmann <arnd@...db.de>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-m68k@...ts.linux-m68k.org, linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: [PATCH] m68k: Fix asm register constraints for atomic ops

Depending on register assignment by the compiler:

    {standard input}:3084: Error: operands mismatch -- statement `andl %a1,%d1' ignored
    {standard input}:3145: Error: operands mismatch -- statement `orl %a1,%d1' ignored
    {standard input}:3195: Error: operands mismatch -- statement `eorl %a1,%d1' ignored

Indeed, the first operand must not be an address register.  Fix this by
adjusting the register constraint from "g" (general purpose register) to
"d" (data register).

Fixes: e39d88ea3ce4a471 ("locking/atomic, arch/m68k: Implement atomic_fetch_{add,sub,and,or,xor}()")
Fixes: d839bae4269aea46 ("locking,arch,m68k: Fold atomic_ops")
Reported-by: kernel test robot <lkp@...el.com>
Reported-by: Arnd Bergmann <arnd@...db.de>
Reported-by: Alexander Viro <viro@...iv.linux.org.uk>
Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
---
Personally, I have never seen this failure in an 68020+ build, but I can
reproduce it on Coldfire with the config provided by lkp (with bogus
CONFIG_RMW_INSNS=y).

Technically, the issue was present before, but I doubt adding pre-v3.18
Fixes tags would make any difference for stable...
---
 arch/m68k/include/asm/atomic.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/m68k/include/asm/atomic.h b/arch/m68k/include/asm/atomic.h
index 8637bf8a2f652009..2d5a6e556754290b 100644
--- a/arch/m68k/include/asm/atomic.h
+++ b/arch/m68k/include/asm/atomic.h
@@ -48,7 +48,7 @@ static inline int arch_atomic_##op##_return(int i, atomic_t *v)		\
 			"	casl %2,%1,%0\n"			\
 			"	jne 1b"					\
 			: "+m" (*v), "=&d" (t), "=&d" (tmp)		\
-			: "g" (i), "2" (arch_atomic_read(v)));		\
+			: "d" (i), "2" (arch_atomic_read(v)));		\
 	return t;							\
 }
 
@@ -63,7 +63,7 @@ static inline int arch_atomic_fetch_##op(int i, atomic_t *v)		\
 			"	casl %2,%1,%0\n"			\
 			"	jne 1b"					\
 			: "+m" (*v), "=&d" (t), "=&d" (tmp)		\
-			: "g" (i), "2" (arch_atomic_read(v)));		\
+			: "d" (i), "2" (arch_atomic_read(v)));		\
 	return tmp;							\
 }
 
-- 
2.25.1