unix: add freebsd/riscv64 support

For golang/go#53466

Change-Id: If5a4dc674cb1856ac580fb87d8030d50fa7c95dd
Reviewed-on: https://go-review.googlesource.com/c/sys/+/416834
Reviewed-by: Benny Siegert <bsiegert@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Run-TryBot: Meng Zhuo <mzh@golangcn.org>
Reviewed-by: Yuval Pavel Zholkover <paulzhol@gmail.com>
Reviewed-by: Dmitri Goutnik <dgoutnik@gmail.com>

unix/syscall_freebsd_riscv64.go

@@ -0,0 +1,63 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build riscv64 && freebsd
+// +build riscv64,freebsd
+
+package unix
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+func setTimespec(sec, nsec int64) Timespec {
+	return Timespec{Sec: sec, Nsec: nsec}
+}
+
+func setTimeval(sec, usec int64) Timeval {
+	return Timeval{Sec: sec, Usec: usec}
+}
+
+func SetKevent(k *Kevent_t, fd, mode, flags int) {
+	k.Ident = uint64(fd)
+	k.Filter = int16(mode)
+	k.Flags = uint16(flags)
+}
+
+func (iov *Iovec) SetLen(length int) {
+	iov.Len = uint64(length)
+}
+
+func (msghdr *Msghdr) SetControllen(length int) {
+	msghdr.Controllen = uint32(length)
+}
+
+func (msghdr *Msghdr) SetIovlen(length int) {
+	msghdr.Iovlen = int32(length)
+}
+
+func (cmsg *Cmsghdr) SetLen(length int) {
+	cmsg.Len = uint32(length)
+}
+
+func sendfile(outfd int, infd int, offset *int64, count int) (written int, err error) {
+	var writtenOut uint64 = 0
+	_, _, e1 := Syscall9(SYS_SENDFILE, uintptr(infd), uintptr(outfd), uintptr(*offset), uintptr(count), 0, uintptr(unsafe.Pointer(&writtenOut)), 0, 0, 0)
+
+	written = int(writtenOut)
+
+	if e1 != 0 {
+		err = e1
+	}
+	return
+}
+
+func Syscall9(num, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r1, r2 uintptr, err syscall.Errno)
+
+func PtraceIO(req int, pid int, addr uintptr, out []byte, countin int) (count int, err error) {
+	ioDesc := PtraceIoDesc{Op: int32(req), Offs: (*byte)(unsafe.Pointer(addr)), Addr: (*byte)(unsafe.Pointer(&out[0])), Len: uint64(countin)}
+	err = ptrace(PT_IO, pid, uintptr(unsafe.Pointer(&ioDesc)), 0)
+	return int(ioDesc.Len), err
+}