My first guess would be that this would involve the go tool invoking the compiler once for each architecture, and then invoking some tool to package the resulting executables into a fat binary.

CC @bcmills @jayconrod

I don't see this happening in the go command in the short term. It would be a major change to juggle multiple architectures during a single command invocation. We've got a lot of modules work left to do for Go 1.16.

It needn't be a feature of go build. A separate tool would be most helpful.

I build & assemble release tarballs for MacOS, Windows, and Linux with a shell script on Linux. That will break down for MacOS without a cross-platform command to create a fat binary.

cc @eliasnaur @hyangah @hajimehoshi

My understanding is that given two ordinary binaries, you can create a fat binary using the lipo command.

EDIT: Is there a lipo for Linux? I haven't found a man page for one.

This is about Darwin, not Linux.

https://ss64.com/osx/lipo.html

Thanks, but that doesn't help. See #40698 (comment) for why I asked about Linux.

lipo is open source, so it can be ported. Here's one attempt: https://github.com/hogliux/cctools (no endorsement implied, YMMV).
It would be great if a lipo tool were written in Go so it could port easily. You could just go get it. I would imagine a lipo tool would be really easy to write, but I haven't investigated deeply.
Regardless, this doesn't have to be in the go tool, at least to start. A go-gettable tool should be fine.

I'd need to know that the authors of a utility that creates binaries for distribution to end users
a) aren't malicious,
b) know what they're doing, and
c) will promptly post fixes if any security issues arise.

The only quick way to vet some-random-lipo is to compare its output with MacOS lipo, and then we're back on square zero.

@networkimprov Sure, but that same problem applies to any utility. We can't put the universe in the Go distribution.
Go has to draw the line somewhere as to what we want to take on with regards to your 3 points. It's not free to take on those responsibilities for a new binary.

The fat binary format is simple. You can see the relevant definitions at https://opensource.apple.com/source/xnu/xnu-344.49/EXTERNAL_HEADERS/mach-o/fat.h.auto.html. The file starts with a fat_header. There are then nfat_arch instances of fat_arch. See the comment in the file. It should only take a couple of hours to write that in a Go program.

A lipo tool doesn't have to land in Go 1.16; the x/ tree is fine for now.

Ian, thanks for the feasibility assessment.

There's a more recent fat.h than the one Ian linked to. It handles files larger than 4GB, among other things.

If you're on a Mac, the header file is at /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/mach-o/fat.h

A good reference: https://stackoverflow.com/questions/46965686/parsing-universal-fat-binary-files

I hacked up a tool that can make fat binaries: https://github.com/randall77/makefat

\o/ thank you!

Readme needs a command line summary.

And it could use a test script to build a hello-world app, run makefat, then launch. Would you accept a patch for that?

Sure.

I verified my script with GOARCH=386 & =amd64. What should it use for Apple Silicon?
With 1.13.3 on Linux, =arm64 doesn't work:

$ GOOS=darwin GOARCH=arm64 go build -o "$test-arm64" "$test.go"
# command-line-arguments
/usr/local/go/pkg/tool/linux_amd64/link: running gcc failed: exit status 1
/usr/bin/ld: unrecognized option '-pagezero_size'
/usr/bin/ld: use the --help option for usage information
collect2: error: ld returned 1 exit status

Also, makefat.go needn't panic if the command-line arguments are incorrect, os.Exit(1) would be fine :-)

arm64

The Apple Silicon port doesn't work yet. I'm working on it.

Wow, it's been exactly an year! I'm sorry for asking, but what's the timeline for progress on this issue?

See https://github.com/randall77/makefat

Hopefully this will land in the golang/x repo someday.

Duplicate of #53281

One of the issues is closed as duplicate of other, while the other was closed by the asking person... I don't think that's correct :) but anyway whatever. That tool works, lipo too.