riscv64: Keep hard-float fenv functions private

riscv64/fenv.c

@@ -26,7 +26,15 @@
  * $FreeBSD: head/lib/msun/riscv/fenv.c 332792 2018-04-19 20:36:15Z brooks $
  */
 
+/*
+ * Keep the hard-float functions private.  The FreeBSD-derived FE_* values are
+ * shifted into fcsr.frm, unlike the raw encodings used on Linux, so exporting
+ * these functions would interpose an incompatible fenv implementation.
+ * Soft-float keeps external definitions because the header only declares them.
+ */
+#ifdef __riscv_float_abi_soft
 #define	__fenv_static
+#endif
 #include <openlibm_fenv.h>
 
 #ifdef __GNUC_GNU_INLINE__
@@ -45,7 +53,6 @@ const fenv_t __fe_dfl_env = {0};
 #define __env_mask(env)                 (0) /* No exception traps. */
 #define __env_round(env)                (((env) >> 5) & _ROUND_MASK)
 #include "fenv-softfloat.h"
-#endif
 
 extern inline int feclearexcept(int __excepts);
 extern inline int fegetexceptflag(fexcept_t *__flagp, int __excepts);
@@ -61,3 +68,4 @@ extern inline int feupdateenv(const fenv_t *__envp);
 extern inline int feenableexcept(int __mask);
 extern inline int fedisableexcept(int __mask);
 extern inline int fegetexcept(void);
+#endif /* __riscv_float_abi_soft */

test/Makefile

@@ -23,8 +23,9 @@ regression-build: $(REGRESSION_BINS)
 
 # -pthread lets thread-safety regressions (e.g. test-222) spawn threads.  It is
 # harmless for the single-threaded tests and is a no-op stub on glibc >= 2.34.
+# -lm lets regressions use platform services that openlibm does not export.
 regression/%: regression/%.c regression/regress-util.h
-	$(CC) $(CPPFLAGS) $(CFLAGS) $(CFLAGS_add) $(LDFLAGS) $(LDFLAGS_arch) $< -D__BSD_VISIBLE -I ../include -I../src $(OPENLIBM_LIB) -pthread -o $@
+	$(CC) $(CPPFLAGS) $(CFLAGS) $(CFLAGS_add) $(LDFLAGS) $(LDFLAGS_arch) $< -D__BSD_VISIBLE -I ../include -I../src $(OPENLIBM_LIB) -lm -pthread -o $@
 
 bench: bench-syslibm bench-openlibm
 

test/regression/test-252.c

@@ -0,0 +1,61 @@
+/*
+ * Regression test for issue #252.  Hard-float RISC-V openlibm used to
+ * interpose its FreeBSD-ABI fenv functions on callers using the incompatible
+ * Linux ABI.  Use the system <fenv.h> and pull in libopenlibm through
+ * isopenlibm().
+ */
+#include <fenv.h>
+
+#include "regress-util.h"
+
+int isopenlibm(void);
+
+#if !defined(__riscv) || defined(__riscv_float_abi_soft) || \
+    !defined(FE_TONEAREST) || !defined(FE_TOWARDZERO) || !defined(FE_UPWARD)
+
+int
+main(void)
+{
+	return REGRESS_SKIP;
+}
+
+#else
+
+/*
+ * Keep the operands volatile and the division out of line: without
+ * -frounding-math the compiler otherwise folds or moves the divisions across
+ * the fesetround() calls.
+ */
+static volatile double one = 1.0, three = 3.0;
+
+static double __attribute__((noinline))
+divide(void)
+{
+	volatile double r = one / three;
+	return r;
+}
+
+int
+main(void)
+{
+	double nearest, down, up;
+
+	CHECK(isopenlibm() == 1);
+
+	nearest = divide();
+	CHECK(fesetround(FE_TOWARDZERO) == 0);
+	CHECK(fegetround() == FE_TOWARDZERO);
+	down = divide();
+	CHECK(fesetround(FE_UPWARD) == 0);
+	CHECK(fegetround() == FE_UPWARD);
+	up = divide();
+	CHECK(fesetround(FE_TONEAREST) == 0);
+	CHECK(fegetround() == FE_TONEAREST);
+
+	/* 1/3 is inexact, so the directed modes must bracket the nearest result. */
+	CHECK(down < up);
+	CHECK(down <= nearest && nearest <= up);
+	return 0;
+}
+
+#endif