internal/syscall/unix: implement Eaccess on all unix platforms

Eaccess, initially added by CL 414824 for linux only, was later
implemented for freebsd (CL 531155), netbsd (CL 531876), dragonfly
(CL 532675), openbsd (CL 538836), and darwin (CL 579976).

The only unix platforms which lack Eaccess are Solaris/Illumos and AIX.

For AIX, syscall.Faccessat is already available, the only missing piece
was AT_EACCESS constant. Let's take it from [1], which, judging by a few
other known AT_ constants, appears to be accurate.

For Solaris, wire the faccessat using the same logic as in the syscall
package.

Now, when we have faccessat for every unix, we can drop eaccess_other.go
and consolidate Eaccess implementations to use faccessat.

[1]: https://github.com/rust-lang/libc/blob/main/src/unix/aix/mod.rs

Change-Id: I7e1b90dedc5d8174235d3a79d5c662f3dcb909c3
Reviewed-on: https://go-review.googlesource.com/c/go/+/611295
Auto-Submit: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Run-TryBot: Kirill Kolyshkin <kolyshkin@gmail.com>

src/internal/syscall/unix/at_aix.go

@@ -9,6 +9,8 @@ package unix
 //go:cgo_import_dynamic libc_unlinkat unlinkat "libc.a/shr_64.o"
 
 const (
+	AT_EACCESS          = 0x1
+	AT_FDCWD            = -0x02
 	AT_REMOVEDIR        = 0x1
 	AT_SYMLINK_NOFOLLOW = 0x1
 	UTIME_OMIT          = -0x3

src/internal/syscall/unix/at_solaris.go

@@ -12,12 +12,15 @@ func syscall6(trap, nargs, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err
 // Implemented as rawsysvicall6 in runtime/syscall_solaris.go.
 func rawSyscall6(trap, nargs, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err syscall.Errno)
 
+//go:cgo_import_dynamic libc_faccessat faccessat "libc.so"
 //go:cgo_import_dynamic libc_fstatat fstatat "libc.so"
 //go:cgo_import_dynamic libc_openat openat "libc.so"
 //go:cgo_import_dynamic libc_unlinkat unlinkat "libc.so"
 //go:cgo_import_dynamic libc_uname uname "libc.so"
 
 const (
+	AT_EACCESS          = 0x4
+	AT_FDCWD            = 0xffd19553
 	AT_REMOVEDIR        = 0x1
 	AT_SYMLINK_NOFOLLOW = 0x1000
 

src/internal/syscall/unix/eaccess.go

@@ -1,11 +1,11 @@
-// Copyright 2022 The Go Authors. All rights reserved.
+// 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 unix
+
 package unix
 
-import "syscall"
-
 func Eaccess(path string, mode uint32) error {
-	return syscall.Faccessat(AT_FDCWD, path, mode, AT_EACCESS)
+	return faccessat(AT_FDCWD, path, mode, AT_EACCESS)
 }

src/internal/syscall/unix/eaccess_other.go

@@ -1,13 +0,0 @@
-// 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 unix && !darwin && !dragonfly && !freebsd && !linux && !openbsd && !netbsd
-
-package unix
-
-import "syscall"
-
-func Eaccess(path string, mode uint32) error {
-	return syscall.ENOSYS
-}

src/internal/syscall/unix/faccessat_bsd.go

@@ -22,7 +22,3 @@ func faccessat(dirfd int, path string, mode uint32, flags int) error {
 	}
 	return err
 }
-
-func Eaccess(path string, mode uint32) error {
-	return faccessat(AT_FDCWD, path, mode, AT_EACCESS)
-}

src/internal/syscall/unix/faccessat_darwin.go

@@ -25,7 +25,3 @@ func faccessat(dirfd int, path string, mode uint32, flags int) error {
 	}
 	return nil
 }
-
-func Eaccess(path string, mode uint32) error {
-	return faccessat(AT_FDCWD, path, mode, AT_EACCESS)
-}

src/internal/syscall/unix/faccessat_openbsd.go

@@ -30,7 +30,3 @@ func faccessat(dirfd int, path string, mode uint32, flags int) error {
 	}
 	return err
 }
-
-func Eaccess(path string, mode uint32) error {
-	return faccessat(AT_FDCWD, path, mode, AT_EACCESS)
-}

src/internal/syscall/unix/faccessat_solaris.go

@@ -0,0 +1,28 @@
+// 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.
+
+package unix
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+//go:linkname procFaccessat libc_faccessat
+
+var procFaccessat uintptr
+
+func faccessat(dirfd int, path string, mode uint32, flags int) error {
+	p, err := syscall.BytePtrFromString(path)
+	if err != nil {
+		return err
+	}
+
+	_, _, errno := syscall6(uintptr(unsafe.Pointer(&procFaccessat)), 4, uintptr(dirfd), uintptr(unsafe.Pointer(p)), uintptr(mode), uintptr(flags), 0, 0)
+	if errno != 0 {
+		return errno
+	}
+
+	return nil
+}

src/internal/syscall/unix/faccessat_syscall.go

@@ -0,0 +1,11 @@
+// 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 aix || linux
+
+package unix
+
+import "syscall"
+
+var faccessat = syscall.Faccessat