linux-kernel - [PATCH] riscv/atomic: Fix sign extension for RV64I

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Date:   Thu, 11 Jun 2020 18:32:35 +0000
From:   Nathan Huckleberry <nhuck@...gle.com>
To:     paul.walmsley@...ive.com, palmer@...belt.com, aou@...s.berkeley.edu
Cc:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Nathan Huckleberry <nhuck@...gle.com>
Subject: [PATCH] riscv/atomic: Fix sign extension for RV64I

The argument passed to cmpxchg is not guaranteed to be sign
extended, but lr.w sign extends on RV64I. This makes cmpxchg
fail on clang built kernels when __old is negative.

To fix this, we just cast __old to long which sign extends on
RV64I. With this fix, clang built RISC-V kernels now boot.

Link: https://github.com/ClangBuiltLinux/linux/issues/867
Cc: clang-built-linux@...glegroups.com
Signed-off-by: Nathan Huckleberry <nhuck@...gle.com>
---
 arch/riscv/include/asm/cmpxchg.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/include/asm/cmpxchg.h b/arch/riscv/include/asm/cmpxchg.h
index d969bab4a26b..262e5bbb2776 100644
--- a/arch/riscv/include/asm/cmpxchg.h
+++ b/arch/riscv/include/asm/cmpxchg.h
@@ -179,7 +179,7 @@
 			"	bnez %1, 0b\n"				\
 			"1:\n"						\
 			: "=&r" (__ret), "=&r" (__rc), "+A" (*__ptr)	\
-			: "rJ" (__old), "rJ" (__new)			\
+			: "rJ" ((long)__old), "rJ" (__new)		\
 			: "memory");					\
 		break;							\
 	case 8:								\
@@ -224,7 +224,7 @@
 			RISCV_ACQUIRE_BARRIER				\
 			"1:\n"						\
 			: "=&r" (__ret), "=&r" (__rc), "+A" (*__ptr)	\
-			: "rJ" (__old), "rJ" (__new)			\
+			: "rJ" ((long)__old), "rJ" (__new)		\
 			: "memory");					\
 		break;							\
 	case 8:								\
@@ -270,7 +270,7 @@
 			"	bnez %1, 0b\n"				\
 			"1:\n"						\
 			: "=&r" (__ret), "=&r" (__rc), "+A" (*__ptr)	\
-			: "rJ" (__old), "rJ" (__new)			\
+			: "rJ" ((long)__old), "rJ" (__new)		\
 			: "memory");					\
 		break;							\
 	case 8:								\
@@ -316,7 +316,7 @@
 			"	fence rw, rw\n"				\
 			"1:\n"						\
 			: "=&r" (__ret), "=&r" (__rc), "+A" (*__ptr)	\
-			: "rJ" (__old), "rJ" (__new)			\
+			: "rJ" ((long)__old), "rJ" (__new)		\
 			: "memory");					\
 		break;							\
 	case 8:								\
-- 
2.27.0.278.ge193c7cf3a9-goog