Date: Fri, 17 Jan 2020 21:57:05 +0000 (UTC) From: John Baldwin <jhb@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-12@freebsd.org Subject: svn commit: r356850 - stable/12/sys/riscv/include Message-ID: <202001172157.00HLv5kW031412@repo.freebsd.org>
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Author: jhb Date: Fri Jan 17 21:57:05 2020 New Revision: 356850 URL: https://svnweb.freebsd.org/changeset/base/356850 Log: MFC 353931: 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. Sponsored by: DARPA Modified: stable/12/sys/riscv/include/atomic.h Directory Properties: stable/12/ (props changed) Modified: stable/12/sys/riscv/include/atomic.h ============================================================================== --- stable/12/sys/riscv/include/atomic.h Fri Jan 17 21:39:28 2020 (r356849) +++ stable/12/sys/riscv/include/atomic.h Fri Jan 17 21:57:05 2020 (r356850) @@ -116,7 +116,7 @@ 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); @@ -141,7 +141,7 @@ 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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