internal/syscall/unix: implement Eaccess on openbsd

Like on other BSDs, use faccessat(AT_FDCWD, path, mode, AT_EACCESS)

Change-Id: I80f8d327dd152576165b9206e32dfb749b41d187
Reviewed-on: https://go-review.googlesource.com/c/go/+/538836
Reviewed-by: Carlos Amedee <carlos@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>

src/internal/syscall/unix/asm_openbsd.s

@@ -0,0 +1,10 @@
+// Copyright 2024 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 && !mips64
+
+#include "textflag.h"
+
+TEXT ·libc_faccessat_trampoline(SB),NOSPLIT,$0-0
+        JMP	libc_faccessat(SB)

src/internal/syscall/unix/at_sysnum_openbsd.go

@@ -10,7 +10,11 @@ const unlinkatTrap uintptr = syscall.SYS_UNLINKAT
 const openatTrap uintptr = syscall.SYS_OPENAT
 const fstatatTrap uintptr = syscall.SYS_FSTATAT
 
-const AT_REMOVEDIR = 0x08
-const AT_SYMLINK_NOFOLLOW = 0x02
+const (
+	AT_EACCESS          = 0x1
+	AT_FDCWD            = -0x64
+	AT_REMOVEDIR        = 0x08
+	AT_SYMLINK_NOFOLLOW = 0x02
 
-const UTIME_OMIT = -0x1
+	UTIME_OMIT = -0x1
+)

src/internal/syscall/unix/eaccess_bsd.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build dragonfly || freebsd || netbsd
+//go:build dragonfly || freebsd || netbsd || (openbsd && mips64)
 
 package unix
 

src/internal/syscall/unix/eaccess_openbsd.go

@@ -0,0 +1,36 @@
+// Copyright 2024 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 && !mips64
+
+package unix
+
+import (
+	"internal/abi"
+	"syscall"
+	"unsafe"
+)
+
+//go:linkname syscall_syscall6 syscall.syscall6
+func syscall_syscall6(fn, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err syscall.Errno)
+
+func libc_faccessat_trampoline()
+
+//go:cgo_import_dynamic libc_faccessat faccessat "libc.so"
+
+func faccessat(dirfd int, path string, mode uint32, flags int) error {
+	p, err := syscall.BytePtrFromString(path)
+	if err != nil {
+		return err
+	}
+	_, _, errno := syscall_syscall6(abi.FuncPCABI0(libc_faccessat_trampoline), uintptr(dirfd), uintptr(unsafe.Pointer(p)), uintptr(mode), uintptr(flags), 0, 0)
+	if errno != 0 {
+		return errno
+	}
+	return err
+}
+
+func Eaccess(path string, mode uint32) error {
+	return faccessat(AT_FDCWD, path, mode, AT_EACCESS)
+}

src/internal/syscall/unix/eaccess_other.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build unix && !dragonfly && !freebsd && !linux && !netbsd
+//go:build unix && !dragonfly && !freebsd && !linux && !openbsd && !netbsd
 
 package unix