svn commit: r356850 - stable/12/sys/riscv/include

[John Baldwin]

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);