linux-kernel - [RESEND,PATCH] ARM: fix __div64_32() error when compiling with clang

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Message-Id: <20201123073634.6854-1-swpenim@gmail.com>
Date:   Mon, 23 Nov 2020 15:36:32 +0800
From:   Antony Yu <swpenim@...il.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     swpenim@...il.com, Russell King <linux@...linux.org.uk>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com
Subject: [RESEND,PATCH] ARM: fix __div64_32() error when compiling with clang

__do_div64 clobbers the input register r0 in little endian system.
According to the inline assembly document, if an input operand is
modified, it should be tied to a output operand. This patch can
prevent compilers from reusing r0 register after asm statements.

Signed-off-by: Antony Yu <swpenim@...il.com>
---
 arch/arm/include/asm/div64.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/arm/include/asm/div64.h b/arch/arm/include/asm/div64.h
index 898e9c78a7e7..809efc51e90f 100644
--- a/arch/arm/include/asm/div64.h
+++ b/arch/arm/include/asm/div64.h
@@ -39,9 +39,10 @@ static inline uint32_t __div64_32(uint64_t *n, uint32_t base)
 	asm(	__asmeq("%0", __xh)
 		__asmeq("%1", "r2")
 		__asmeq("%2", "r0")
-		__asmeq("%3", "r4")
+		__asmeq("%3", "r0")
+		__asmeq("%4", "r4")
 		"bl	__do_div64"
-		: "=r" (__rem), "=r" (__res)
+		: "=r" (__rem), "=r" (__res), "=r" (__n)
 		: "r" (__n), "r" (__base)
 		: "ip", "lr", "cc");
 	*n = __res;
-- 
2.23.0