runtime,syscall: convert syscall on openbsd/amd64 to libc

Convert the syscall package on openbsd/amd64 to use libc rather than performing
direct system calls.

Updates #36435

Change-Id: Ieb5926a91ed34f7c722e3667004ec484c86804ef
Reviewed-on: https://go-review.googlesource.com/c/go/+/270380
Trust: Joel Sing <joel@sing.id.au>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>

src/syscall/syscall_openbsd_libc.go

@@ -0,0 +1,93 @@
+// Copyright 2020 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.
+
+// +build openbsd,amd64
+
+package syscall
+
+import "unsafe"
+
+//sys directSyscall(trap uintptr, a1 uintptr, a2 uintptr, a3 uintptr, a4 uintptr, a5 uintptr) (ret uintptr, err error) = SYS_syscall
+
+func syscallInternal(trap, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno) {
+	return syscall6X(funcPC(libc_syscall_trampoline), trap, a1, a2, a3, 0, 0)
+}
+
+func syscall6Internal(trap, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno) {
+	return syscall10X(funcPC(libc_syscall_trampoline), trap, a1, a2, a3, a4, a5, a6, 0, 0, 0)
+}
+
+func rawSyscallInternal(trap, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno) {
+	return rawSyscall6X(funcPC(libc_syscall_trampoline), trap, a1, a2, a3, 0, 0)
+}
+
+func rawSyscall6Internal(trap, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno) {
+	return rawSyscall10X(funcPC(libc_syscall_trampoline), trap, a1, a2, a3, a4, a5, a6, 0, 0, 0)
+}
+
+func syscall9Internal(trap, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r1, r2 uintptr, err Errno) {
+	return rawSyscall10X(funcPC(libc_syscall_trampoline), trap, a1, a2, a3, a4, a5, a6, a7, a8, a9)
+}
+
+// Implemented in the runtime package (runtime/sys_openbsd3.go)
+func syscall(fn, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno)
+func syscallX(fn, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno)
+func syscall6(fn, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno)
+func syscall6X(fn, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno)
+func syscall10(fn, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10 uintptr) (r1, r2 uintptr, err Errno)
+func syscall10X(fn, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10 uintptr) (r1, r2 uintptr, err Errno)
+func rawSyscall(fn, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno)
+func rawSyscall6(fn, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno)
+func rawSyscall6X(fn, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno)
+func rawSyscall10X(fn, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10 uintptr) (r1, r2 uintptr, err Errno)
+
+func syscall9(fn, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r1, r2 uintptr, err Errno) {
+	return syscall10(fn, a1, a2, a3, a4, a5, a6, a7, a8, a9, 0)
+}
+func syscall9X(fn, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r1, r2 uintptr, err Errno) {
+	return syscall10X(fn, a1, a2, a3, a4, a5, a6, a7, a8, a9, 0)
+}
+
+// Find the entry point for f. See comments in runtime/proc.go for the
+// function of the same name.
+//go:nosplit
+func funcPC(f func()) uintptr {
+	return **(**uintptr)(unsafe.Pointer(&f))
+}
+
+//sys	Seek(fd int, offset int64, whence int) (newoffset int64, err error) = SYS_lseek
+//sys	getcwd(buf []byte) (n int, err error)
+//sys	sysctl(mib []_C_int, old *byte, oldlen *uintptr, new *byte, newlen uintptr) (err error)
+//sysnb fork() (pid int, err error)
+//sysnb ioctl(fd int, req int, arg int) (err error)
+//sysnb execve(path *byte, argv **byte, envp **byte) (err error)
+//sysnb exit(res int) (err error)
+//sys   ptrace(request int, pid int, addr uintptr, data uintptr) (err error)
+//sysnb getentropy(p []byte) (err error)
+//sys   fstatat(fd int, path string, stat *Stat_t, flags int) (err error)
+//sys	fcntlPtr(fd int, cmd int, arg unsafe.Pointer) (val int, err error) = SYS_fcntl
+//sys   unlinkat(fd int, path string, flags int) (err error)
+//sys   openat(fd int, path string, flags int, perm uint32) (fdret int, err error)
+
+func init() {
+	execveOpenBSD = execve
+}
+
+func readlen(fd int, buf *byte, nbuf int) (n int, err error) {
+	r0, _, e1 := syscall(funcPC(libc_read_trampoline), uintptr(fd), uintptr(unsafe.Pointer(buf)), uintptr(nbuf))
+	n = int(r0)
+	if e1 != 0 {
+		err = errnoErr(e1)
+	}
+	return
+}
+
+func writelen(fd int, buf *byte, nbuf int) (n int, err error) {
+	r0, _, e1 := syscall(funcPC(libc_write_trampoline), uintptr(fd), uintptr(unsafe.Pointer(buf)), uintptr(nbuf))
+	n = int(r0)
+	if e1 != 0 {
+		err = errnoErr(e1)
+	}
+	return
+}