os: there is no procfs on OpenBSD

[darinkes]

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

go version go1.8 openbsd/amd64

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

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="openbsd"
GOOS="openbsd"
GOPATH="/home/srinkes/go_work/"
GORACE=""
GOROOT="/usr/local/go"
GOTOOLDIR="/usr/local/go/pkg/tool/openbsd_amd64"
GCCGO="gccgo"
CC="cc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0"
CXX="c++"
CGO_ENABLED="1"
PKG_CONFIG="pkg-config"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"

What did you do?

Compiled and started gitlab-ci-multi-runner on openbsd/amd64.
On startup I see this Warning:

WARN[0000] readlink /proc/curproc/file: no such file or directory

Apparently go tries to Readlink /proc/curproc/file in https://github.com/golang/go/blob/master/src/os/executable_procfs.go#L26

But there is no (optional) procfs on OpenBSD anymore. mount_procfs(8) was shipped last time with OpenBSD 5.5:

http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/sbin/mount_procfs/

  2 years ago:
  Delete procfs; it's always had races and is now unused: no one noticed for month...

[darinkes]

Ok, in my case it seems its not coming from go core, but from https://github.com/kardianos/osext/blob/master/osext_procfs.go

Which also had nearly the same code as in go core:

        case "openbsd", "dragonfly":
                return os.Readlink("/proc/curproc/file")

But this was removed with this commit:
kardianos/osext@b4814f4

Maybe go core should do the same thing?

[darinkes]

And with this commit it uses the core executable(). So an update of osext won't fix this if you want to use go 1.8:
kardianos/osext@9b883c5

[bradfitz]

/cc @mdempsky

[mdempsky]

The report is correct: there's no procfs on OpenBSD. But unfortunately, there's also no alternative kernel API for implementing os.Executable. (This has a long contentious history within OpenBSD.)

So at best we can emit a better "not implemented" error instead of complaining that /proc doesn't exist.

Or we can try looking for os.Argv[0] in $PATH, and hope it's right. (I believe this is what apps ported to OpenBSD usually do when trying to port this functionality.)

[ianlancetaylor]

CC @minux

[darinkes]

As mentioned kardianos/osext has an workaround for this problem from an OpenBSD Developer: kardianos/osext@b4814f4

Maybe this can be included in go core?
(I have no opinion if this is a bad or good workaround)

CC @ajacoutot

[ajacoutot]

What I implemented in osext is not a workaround per se; as mentioned it's a "best effort" :-)
As @mdempsky said, the history behind implementing such a functionality in OpenBSD has been complex... and I wouldn't expect it to change.
The result is that apps implement it themselves which is why I think it'd make sense to have something in go core if possible.

[bradfitz]

@ianlancetaylor will copy the gccgo AIX code for argv[0] into std for openbsd.

And then enable the test:

func TestExecutable(t *testing.T) {
        testenv.MustHaveExec(t) // will also execlude nacl, which doesn't support Executable anyway                                                        
        ep, err := os.Executable()
        if err != nil {
                switch goos := runtime.GOOS; goos {
                case "openbsd": // procfs is not mounted by default                                                                                        
                        t.Skipf("Executable failed on %s: %v, expected", goos, err)
                }

We have OpenBSD trybots.

[gopherbot]

CL https://golang.org/cl/46004 mentions this issue.