syscall/js: add support for fork/exec syscalls?

[myitcv]

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

$ go version
go version devel +b7689f5aa3 Fri Jan 31 06:02:00 2020 +0000 linux/amd64

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="on"
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/myitcv/.cache/go-build"
GOENV="/home/myitcv/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/myitcv/gostuff"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/myitcv/gos"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/myitcv/gos/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/myitcv/gostuff/src/github.com/myitcv/playground/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build703123889=/tmp/go-build -gno-record-gcc-switches"

What did you do?

-- go.mod --
module mod

-- main.go --
package main

import (
        "fmt"
        "os"
        "os/exec"
)

func main() {
        cmd := exec.Command("echo", "hello")
        cmd.Stdout = os.Stdout
        cmd.Stderr = os.Stderr
        if err := cmd.Run(); err != nil {
                fmt.Fprintln(os.Stderr, err)
                os.Exit(1)
        }
}

GOOS=js GOARCH=wasm go build -o main.wasm
$(go env GOROOT)/misc/wasm/go_js_wasm_exec main.wasm

What did you expect to see?

hello

What did you see instead?

exec: "echo": executable file not found in $PATH

As some folks on Slack kindly pointed out, this is because GOOS=js ARCH=wasm does not support fork/exec syscalls. Those same folks were not clear that it made sense for this to be supported (especially given the browser focus of this port), but when executing through NodeJS (i.e. the go_js_wasm_exec wrapper) it does have meaning.

Thoughts?

cc @neelance

[smasher164]

With the current GOOS=js, we would either need an environment variable like FORKEXEC=on, or some runtime feature detection to allow such a call to take place.

That being said, I think that the general solution to this problem would be to support GOOS=wasi as per #31105. However, the current WASI spec defers fork/exec to a post-MVP version because it is hard to extend to a capability-based design, and doesn't translate well to platforms (windows/web) that can't emulate the syscalls efficiently.

[neelance]

Fork is a very difficult syscall. I don't see an easy way to support it with Node.js. It is unlikely that I will work on this. Maybe someone else wants to try...

[gopherbot]

Change https://golang.org/cl/260717 mentions this issue: singleflight: skip tests involving exec on js/wasm