x/sys/unix: Missing AT_EACCESS on non-Linux Unix systems

[MKuranowski]

What version of Go are you using (go version)?

$ go version
go version go1.20.2 darwin/amd64
$ tail -n 1 go.mod
require golang.org/x/sys v0.6.0

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/mk/Library/Caches/go-build"
GOENV="/Users/mk/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/mk/.local/share/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/mk/.local/share/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/Cellar/go/1.20.2/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.20.2/libexec/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="go1.20.2"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/dev/null"
GOWORK=""
CGO_CFLAGS="-O2 -g"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-O2 -g"
CGO_FFLAGS="-O2 -g"
CGO_LDFLAGS="-O2 -g"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/7l/56csh9n54g503487v94kb2pm0000gp/T/go-build1532737799=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

https://go.dev/play/p/yqd7iBRFmEV

package main

import (
	"fmt"

	"golang.org/x/sys/unix"
)

func main() {
	err := unix.Faccessat(unix.AT_FDCWD, "/bin/sh", unix.X_OK, unix.AT_EACCESS)
	fmt.Println(err)
}

What did you expect to see?

Program to run and (most likely) print <nil>.

What did you see instead?

Compilation error:

$ go run access.go
# command-line-arguments
./access.go:10:66: undefined: unix.AT_EACCESS

Comment

AT_EACCESS is specified by the POSIX standard, in the fcntl.h header; used by the faccessat syscall.

If the latter syscall is exposed, I don't see any reason why the AT_EACCESS constant is not provided.

Looking through the source code of the x/sys/unix package however, AT_EACCESS seems to only be available on Linux AT_EACCESS is missing from AIX and Darwin.

Workaround

I can workaround the issue by using CGo and manually poking at fcntl.h.

package main

import (
	"fmt"

	"golang.org/x/sys/unix"
)

// #include <fcntl.h>
import "C"

func main() {
	err := unix.Faccessat(unix.AT_FDCWD, "/bin/sh", unix.X_OK, C.AT_EACCESS)
	fmt.Println(err)
}

$ go run access.go
<nil>

[ianlancetaylor]

I think this is just missing. Want to send a patch?

[MKuranowski]

Made a PR: golang/sys#153

[gopherbot]

Change https://go.dev/cl/480115 mentions this issue: unix: add AT_EACCESS on Darwin