libc: Provide sub fp(s|g)etmask() implementations for RISC-V

RISC-V doesn't support floating-point exceptions.

RISC-V Instruction Set Manual: Volume I: User-Level ISA, 11.2 Floating-Point
Control and Status Register: "As allowed by the standard, we do not support
traps on floating-point exceptions in the base ISA, but instead require
explicit checks of the flags in software. We considered adding branches
controlled directly by the contents of the floating-point accrued exception
flags, but ultimately chose to omit these instructions to keep the ISA simple."

We still need these functions, because some applications (notably Perl) call
them, but we cannot provide a meaningful implementation.

Sponsored by:	Axiado
Differential Revision:	https://reviews.freebsd.org/D25740

lib/libc/riscv/gen/Makefile.inc

@@ -3,6 +3,8 @@
 SRCS+=	_ctx_start.S \
 	fabs.S \
 	flt_rounds.c \
+	fpgetmask.c \
+	fpsetmask.c \
 	infinity.c \
 	ldexp.c \
 	makecontext.c \

lib/libc/riscv/gen/fpgetmask.c

@@ -0,0 +1,41 @@
+/*-
+ * Copyright (c) 2020 Axiado
+ * All rights reserved.
+ *
+ * This software was developed by Kristof Provost under
+ * sponsorship from Axiado.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/types.h>
+#include <ieeefp.h>
+
+fp_except_t
+fpgetmask(void)
+{
+
+	return (0);
+}

lib/libc/riscv/gen/fpsetmask.c

@@ -0,0 +1,53 @@
+/*-
+ * Copyright (c) 2020 Axiado
+ * All rights reserved.
+ *
+ * This software was developed by Kristof Provost under
+ * sponsorship from Axiado.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/types.h>
+#include <ieeefp.h>
+
+/**
+ * RISC-V doesn't support floating-point exceptions: RISC-V Instruction Set
+ * Manual: Volume I: User-Level ISA, 11.2 Floating-Point Control and Status
+ * Register: "As allowed by the standard, we do not support traps on
+ * floating-point exceptions in the base ISA, but instead require explicit
+ * checks of the flags in software. We considered adding branches controlled
+ * directly by the contents of the floating-point accrued exception flags, but
+ * ultimately chose to omit these instructions to keep the ISA simple." 
+ *
+ * We still need this function, because some applications (notably Perl) call
+ * it, but we cannot provide a meaningful implementation.
+ **/
+fp_except_t
+fpsetmask(fp_except_t mask)
+{
+
+	return (0);
+}

sys/riscv/include/ieeefp.h

@@ -4,5 +4,6 @@
 #define	_MACHINE_IEEEFP_H_
 
 /* TODO */
+typedef int fp_except_t;
 
 #endif /* _MACHINE_IEEEFP_H_ */