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Date:   Thu, 11 Jun 2020 18:32:35 +0000
Message-Id: <20200611183235.37508-1-nhuck@google.com>
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Subject: [PATCH] riscv/atomic: Fix sign extension for RV64I
From:   Nathan Huckleberry <nhuck@google.com>
To:     paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu
Cc:     linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        clang-built-linux@googlegroups.com,
        Nathan Huckleberry <nhuck@google.com>
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Sender: linux-kernel-owner@vger.kernel.org
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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@googlegroups.com
Signed-off-by: Nathan Huckleberry <nhuck@google.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