Prevent module from closing when proc_exit is called with a 0 exit code

[pkedy]

The latest stable release of TinyGo (0.35.0) invokes the WASI proc_exit syscall when the _start function is complete, even if the exit code is 0. Frameworks that use wazero likely expect an empty main() and call other exported functions. Because the module closes, this is broken in TinyGo 0.35.0. Any call thereafter also return sys.ExitError and basic host calls like fmt.Println are likely to panic.

This PR fixes the issue by returning out of procExitFn before closing the module if the exit code is 0.
Fixes #2357

The host program may still need to handle sys.ExitError being returned from _start. That does not change.

[anuraaga]

Hi @pkedy - AFAIK this isn't correct for CLIs which cannot be used after the module exits.

To use exported functions, the wasm needs to be built as c-shared. I updated the docs in https://github.com/tetratelabs/wazero/pull/2368/files#diff-fe83992f154cc181844b6bf965a0b6aba367c7b498a3a0db43b5b212d041531bR22

[pkedy]

I'm looking into this from the perspective of a plugin library, which uses main() for set up some initial state for future calls.

I just tried -buildmode=c-shared and what I'm seeing is that state gets cleared out and my calls to other functions fails as a result. I'll keep digging into this.

[anuraaga]

Ah also in case you missed it, the other change is to update WithStartFunctions("_initialize")

https://github.com/tetratelabs/wazero/pull/2368/files#diff-45c4202edd75629cf297edd9f2aa1d914fb21e0f4ac4235a673d185596dff610R45

I'm not sure if TinyGo would then expect initialization logic to be in init() or if main() would continue to work, but that would be an issue on TinyGo side if it's not supported.

I'm looking into this from the perspective of a plugin library,

Yeah before these were conflated with CLIs in the Go ecosystem, which didn't match the WASI spec, but now are distinct, with CLIs being the standard output and reactors (plugin libraries) being the c-shared buildmode output.

[pkedy]

@anuraaga OK. Yep. Got it working. All makes sense now. While it 100% makes sense, it will take some time/effort for the TinyGo WASM community to transition to these changes. Thanks for educating me on this!