Lack of "_start" export causes exception. Use standard (start ...) instead about lucet HOT 4 CLOSED

There is a subtlety here: at the time when the wasm start function is called, code outside the module cannot access the module's exports. So if the wasm start function calls some code that expects to be able to call back into the wasm, it won't work. It remains an open question whether such cyclic dependency patterns should be supported in wasm. The WASI libc uses an exported function named _start right now, instead of a wasm start function, to avoid these issues.

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@sunfishcode ah, because the start function is intended to be called during instantiation of the module right? That makes sense. So I guess the real issue is that lucet is throwing an exception when "_start" isn't exported whereas wasmtime is not (or it is but is swallowing the exception). Also, perhaps a different name than "_start" so it doesn't get as easily confused with the start function (like it did for me)? "_main" or "_entry" perhaps?

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I agree, _start is confusing. I filed WebAssembly/WASI#19 to track changing the name.

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I'm going to close this for now; we'll be sure to adapt what lucet-wasi does to match the behavior that results from the WebAssembly/WASI#19 discussion. Until then, we will need to keep the current behavior of running the wasm start function on instantiation, and then calling an exported _start function for the main program.

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