Date: Wed, 23 Oct 2019 16:41:32 +0000 (UTC) From: John Baldwin <jhb@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r353931 - head/sys/riscv/include Message-ID: <201910231641.x9NGfWeU031407@repo.freebsd.org>
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Author: jhb Date: Wed Oct 23 16:41:31 2019 New Revision: 353931 URL: https://svnweb.freebsd.org/changeset/base/353931 Log: 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 Modified: head/sys/riscv/include/atomic.h Modified: head/sys/riscv/include/atomic.h ============================================================================== --- head/sys/riscv/include/atomic.h Wed Oct 23 16:06:47 2019 (r353930) +++ head/sys/riscv/include/atomic.h Wed Oct 23 16:41:31 2019 (r353931) @@ -182,7 +182,7 @@ atomic_cmpset_32(volatile uint32_t *p, uint32_t cmpval "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 *cmpv "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);
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