From 8eea4337db704e6ab4465838c17f0ab41e710c59 Mon Sep 17 00:00:00 2001 From: jhb Date: Wed, 23 Oct 2019 16:41:31 +0000 Subject: [PATCH] Fix atomic_*cmpset32 on riscv64 with clang. The lr.w instruction used to read the value from memory sign-extends the value read from memory. GCC sign-extends the 32-bit comparison value passed in whereas clang currently does not. As a result, if the value being compared has the MSB set, the comparison fails for matching 32-bit values when compiled with clang. Use a cast to explicitly sign-extend the unsigned comparison value. This works with both GCC and clang. There is commentary in the RISC-V spec that suggests that GCC's approach is more correct, but it is not clear if the commentary in the RISC-V spec is binding. Reviewed by: mhorne Obtained from: Axiado MFC after: 2 weeks Sponsored by: DARPA Differential Revision: https://reviews.freebsd.org/D22084 --- sys/riscv/include/atomic.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/sys/riscv/include/atomic.h b/sys/riscv/include/atomic.h index 877caf40a0ad..7f713dfc095a 100644 --- a/sys/riscv/include/atomic.h +++ b/sys/riscv/include/atomic.h @@ -182,7 +182,7 @@ atomic_cmpset_32(volatile uint32_t *p, uint32_t cmpval, uint32_t newval) "bnez %1, 0b\n" "1:" : "=&r" (tmp), "=&r" (res), "+A" (*p) - : "rJ" (cmpval), "rJ" (newval) + : "rJ" ((long)(int32_t)cmpval), "rJ" (newval) : "memory"); return (!res); @@ -207,7 +207,7 @@ atomic_fcmpset_32(volatile uint32_t *p, uint32_t *cmpval, uint32_t newval) "sw %0, %3\n" /* Save old value */ "2:" : "=&r" (tmp), "=&r" (res), "+A" (*p), "+A" (*cmpval) - : "rJ" (*cmpval), "rJ" (newval) + : "rJ" ((long)(int32_t)*cmpval), "rJ" (newval) : "memory"); return (!res);