proposal: all: add GOOS=cosmo port for Cosmopolitan Libc

[borancar]

Go is slowly becoming the de-facto lingua franca of DevOps - to the point of replacing shell scripting (see Cloudflare Blog/Using Go as a scripting language in Linux). The next great iteration would be a compile once run anywhere type of such scripting (as possible as it can be with external packaging involved). There's already a PoC libc and executable format that can run anywhere (see Cosmopolitan libc and APE). The author of Cosmpolitan and APE has indicated a willingness to collaborate and support Go running on Cosmopolitan and producing APE binaries.

[ianlancetaylor]

Without looking too hard, I think this would effectively mean porting Go to a new GOOS value. See https://go.dev/wiki/PortingPolicy.

It would be interesting to hear how much work this would be. To be clear, it is extremely unlikely that anybody on the core Go team would work on this. But if someone is interested in working on it, and can satisfy the porting policy, we could consider adding the port.

[dmitshur]

CC @golang/release, @aclements as FYI.

[rsc]

It does sound like this would be a new operating system, which somehow is the union of all existing operating systems.
How does Cosmopolitan libc measure up against the requirements in #53383?

And what would the changes look like in the runtime?
I am a little scared of the "union of all systems" aspect of this.
If Cosmopolitan libc is taking care of all this, where would Go find the libc object to link in?

[rsc]

This proposal has been added to the active column of the proposals project
and will now be reviewed at the weekly proposal review meetings.
— rsc for the proposal review group

[jart]

Cosmopolitan Libc author here. Thank you for considering this proposal. Our project would love the opportunity to support the Go community.

[jart]

To answer @rsc's questions:

And what would the changes look like in the runtime?

Try taking an existing libc integration (e.g. go/src/runtime/sys_openbsd2.go) and using that with cosmopolitan.h and cosmopolitan.a. You need to use ld.bfd to link your binaries unless you generate the APE executable format on your own. Cosmopolitan assumes your entrypoint will be main(). Everything is System V ABI. We do backtraces using %rbp. We log function calls using mcount. If you want TLS on all operating systems then you need to devote both %fs and %gs since the latter is dynamically rewritten on Windows and Apple platforms. If Go has register requirements that aren't SysV you can tune the build using flags like -ffixed-rbx. Any place where you've hardcoded system-related magic numbers (e.g. EPERM) would need to be modified to fetch it from an extern errno_t instead.

I am a little scared of the "union of all systems" aspect of this.

Cosmopolitan is the union of all operating systems in the sense that jQuery was the union of all web browsers. The only big thing we changed was we made POSIX defines symbolic. For example, #define EPERM 1 is now extern errno_t EPERM;. That let us abstract most of the portability issues between UNIX variants. Then we wrote system call veneers that polyfill behavior differences between platforms like Windows. https://justine.lol/ape.html

If Cosmopolitan libc is taking care of all this, where would Go find the libc object to link in?

Consider using one of our pinned "amalgamation" releases. We put everything in a giant static archive. You need cosmopolitan.a, crt.o, ape-no-modify-self.o, ape.lds, and cosmopolitan.h which are all in the zip file.

• https://github.com/jart/cosmopolitan/releases/tag/2.0 (latest release)
• https://justine.lol/cosmopolitan/cosmopolitan-amalgamation-2.0.zip (official download link)
• https://worker.jart.workers.dev/cosmopolitan-amalgamation-2.0.zip (please use this free egress mirror for your CIs)

Actual or expected user base. If there are relatively few users, significant effort to maintain a port may not be worthwhile.

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