runtime,os: add os.Executable() for Darwin

[dgryski]

No description provided.

[eliasnaur]

LGTM, other than a single question below.

[eliasnaur]

Why not executablePath := unsafe.String((*byte)(cstr), length)?

[aykevl]

We still support Go 1.19, and unsafe.String was introduced in Go 1.20.

[dgryski]

We don't (yet) use unsafe.String() in the runtime package, although there is a comment to that effect:

tinygo/src/runtime/runtime.go

Line 114 in 3e60eeb

// TODO: use unsafe.String instead once we require Go 1.20.

[eliasnaur]

I see, thanks. I did in fact look up when unsafe.String was introduced but then went ahead and assumed 1.20 was more than safe. Out of curiosity, is there any reason for keeping support for such a old version of Go?

[aykevl]

We could indeed drop support for this older version by now. One consideration might be that Debian bookworm (current stable) uses Go 1.19, dropping support for that means people will need to upgrade the Go version on Debian.

[aykevl]

LGTM assuming you've tested this

[dgryski]

Hmm..

~/go/src/github.com/dgryski/bug/exe $ cat main.go
package main

import "os"

func main() {
	p, err := os.Executable()
	if err != nil {
		println("error: ", err)
	} else {
		println("exe: ", p)
	}
}
~/go/src/github.com/dgryski/bug/exe $ tinygo run main.go
exe:  /var/folders/5b/_hr1d1fd3qn4t9vtfx5p61wm0000gp/T/tinygo2514738286/main
~/go/src/github.com/dgryski/bug/exe $ tinygo build
~/go/src/github.com/dgryski/bug/exe $ ./exe
exe:  ./exe
~/go/src/github.com/dgryski/bug/exe $ go run main.go
exe:  /var/folders/5b/_hr1d1fd3qn4t9vtfx5p61wm0000gp/T/go-build1161502719/b001/exe/main
~/go/src/github.com/dgryski/bug/exe $ go build
~/go/src/github.com/dgryski/bug/exe $ ./exe
exe:  /Users/dgryski/go/src/github.com/dgryski/bug/exe/exe

Big Go gives the full path but we only get the relative path for a full binary. I should probably fix that.

[deadprogram]

Thanks for the addition @dgryski and to @eliasnaur and @aykevl for reviewing. Now merging.

[aykevl]

@dgryski I suspect the result is wrong if you call os.Chdir and then call os.Executable().

[dgryski]

Oops, oh right. I guess we need to do the entire resolution at process startup instead. I'll rework this (although it means adding in a hook to main() to call any platform-specific argc/argv processing).

[dgryski]

Fix for os.Chdir issue: #4881