unix: convert openbsd/arm64 to direct libc calls

The current code has continued to work on OpenBSD, since it has been using
syscall(2) via libc. However, the system call numbers are still hardcoded in
golang.org/sys/unix. Various system call changes have been made in OpenBSD,
resulting in changes to the system call numbers and arguments, which now
fail when this package is used.

Switch to calling various system calls directly via libc, rather than calling
via libc using syscall(2).

Updates golang/go#36435

Change-Id: I836a484b14e0a427ac565315e27f0de1e9a5d021
Reviewed-on: https://go-review.googlesource.com/c/sys/+/421796
Reviewed-by: Ian Lance Taylor <[email protected]>
Reviewed-by: Tobias Klauser <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Ian Lance Taylor <[email protected]>
Reviewed-by: Than McIntosh <[email protected]>

Author: 4a6f656c

unix/mkall.sh

@@ -165,10 +165,10 @@ openbsd_arm)
 	mktypes="GOARCH=$GOARCH go tool cgo -godefs -- -fsigned-char"
 	;;
 openbsd_arm64)
+	mkasm="go run mkasm.go"
 	mkerrors="$mkerrors -m64"
-	mksyscall="go run mksyscall.go -openbsd"
+	mksyscall="go run mksyscall.go -openbsd -libc"
 	mksysctl="go run mksysctl_openbsd.go"
-	mksysnum="go run mksysnum.go 'https://cvsweb.openbsd.org/cgi-bin/cvsweb/~checkout~/src/sys/kern/syscalls.master'"
 	# Let the type of C char be signed for making the bare syscall
 	# API consistent across platforms.
 	mktypes="GOARCH=$GOARCH go tool cgo -godefs -- -fsigned-char"

unix/mksyscall.go

@@ -36,13 +36,16 @@ import (
 var (
 	b32       = flag.Bool("b32", false, "32bit big-endian")
 	l32       = flag.Bool("l32", false, "32bit little-endian")
+	libc      = flag.Bool("libc", false, "libc system calls")
 	plan9     = flag.Bool("plan9", false, "plan9")
 	openbsd   = flag.Bool("openbsd", false, "openbsd")
 	netbsd    = flag.Bool("netbsd", false, "netbsd")
 	dragonfly = flag.Bool("dragonfly", false, "dragonfly")
 	arm       = flag.Bool("arm", false, "arm") // 64-bit value should use (even, odd)-pair
 	tags      = flag.String("tags", "", "build tags")
 	filename  = flag.String("output", "", "output file name (standard output if omitted)")
+
+	libcPath = "libc.so"
 )
 
 // cmdLine returns this programs's commandline arguments
@@ -124,10 +127,11 @@ func main() {
 		endianness = "little-endian"
 	}
 
-	libc := false
 	if goos == "darwin" {
-		libc = true
+		libcPath = "/usr/lib/libSystem.B.dylib"
+		*libc = true
 	}
+
 	trampolines := map[string]bool{}
 
 	text := ""
@@ -210,7 +214,7 @@ func main() {
 					text += fmt.Sprintf(" else {\n\t\t_p%d = unsafe.Pointer(&_zero)\n\t}\n", n)
 					args = append(args, fmt.Sprintf("uintptr(_p%d)", n), fmt.Sprintf("uintptr(len(%s))", p.Name))
 					n++
-				} else if p.Type == "int64" && (*openbsd || *netbsd) {
+				} else if p.Type == "int64" && ((*openbsd && !*libc) || *netbsd) {
 					args = append(args, "0")
 					if endianness == "big-endian" {
 						args = append(args, fmt.Sprintf("uintptr(%s>>32)", p.Name), fmt.Sprintf("uintptr(%s)", p.Name))
@@ -285,10 +289,18 @@ func main() {
 			}
 
 			var libcFn string
-			if libc {
+			if *libc {
 				asm = "syscall_" + strings.ToLower(asm[:1]) + asm[1:] // internal syscall call
 				sysname = strings.TrimPrefix(sysname, "SYS_")         // remove SYS_
 				sysname = strings.ToLower(sysname)                    // lowercase
+				if *openbsd && *libc {
+					switch sysname {
+					case "__getcwd":
+						sysname = "getcwd"
+					case "__sysctl":
+						sysname = "sysctl"
+					}
+				}
 				libcFn = sysname
 				sysname = "libc_" + sysname + "_trampoline_addr"
 			}
@@ -360,14 +372,14 @@ func main() {
 			text += "\treturn\n"
 			text += "}\n\n"
 
-			if libc && !trampolines[libcFn] {
+			if *libc && !trampolines[libcFn] {
 				// some system calls share a trampoline, like read and readlen.
 				trampolines[libcFn] = true
 				// Declare assembly trampoline address.
 				text += fmt.Sprintf("var libc_%s_trampoline_addr uintptr\n\n", libcFn)
 				// Assembly trampoline calls the libc_* function, which this magic
 				// redirects to use the function from libSystem.
-				text += fmt.Sprintf("//go:cgo_import_dynamic libc_%s %s \"/usr/lib/libSystem.B.dylib\"\n", libcFn, libcFn)
+				text += fmt.Sprintf("//go:cgo_import_dynamic libc_%s %s %q\n", libcFn, libcFn, libcPath)
 				text += "\n"
 			}
 		}

unix/syscall_openbsd_libc.go

@@ -0,0 +1,21 @@
+// 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 openbsd && arm64
+// +build openbsd,arm64
+
+package unix
+
+import _ "unsafe"
+
+// Implemented in the runtime package (runtime/sys_openbsd3.go)
+func syscall_syscall(fn, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno)
+func syscall_syscall6(fn, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno)
+func syscall_rawSyscall(fn, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno)
+func syscall_rawSyscall6(fn, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno)
+
+//go:linkname syscall_syscall syscall.syscall
+//go:linkname syscall_syscall6 syscall.syscall6
+//go:linkname syscall_rawSyscall syscall.rawSyscall
+//go:linkname syscall_rawSyscall6 syscall.rawSyscall6