wasm2c: Add macro and tests to allow disabling stack exhaustion checks

[shravanrn]

(Continued from #2354)

This PR adds an macro WASM_RT_NONCONFORMING_STACK_UNCHECKED to allow the embedder to unsafely remove all stack checks from wasm2c. This would mean the embedder is not conformant with the Wasm spec. This configuration is useful for embedders like RLBox which are unlikely to be affected by stack exhaustion, and don't want to pay performance penalties for this. The wasm2c build in CI that uses rlbox flags has been correspondingly updated to capture this.

[sbc100]

Seems reasonable to me. IIUC this approach is what you and @keithw disccussed in #2354?

[shravanrn]

Seems reasonable to me. IIUC this approach is what you and @keithw disccussed in #2354?

Yup, I believe so.
@keithw is this what you had in mind?

[keithw]

lgtm % comment. Could we call it WASM_RT_NONCONFORMING_UNCHECKED_STACK_EXHAUSTION or something to be very clear about what's "unchecked" about this?

[shravanrn]

@keithw Done. Could you sign off on the change when you have a chance?

[keithw]

lgtm % comment. I like how minimal this is...

[keithw]

Just saw @sunfishcode's comment on the other thread -- let's hold off on merging (especially since this one is more about sandboxing) to try to get consensus.

[shravanrn]

Just saw @sunfishcode's comment on the other thread -- let's hold off on merging (especially since this one is more about sandboxing) to try to get consensus.

Alright. Fwiw, if we end up not wanting to expose the non-conforming approach on this change, the best path forward for us is to go back to the original commit I had here --- where we add a macro of the form WASM_RT_STACK_EXHAUSTION_CHECKED_BY_EMBEDDER which basically say its the host's responsibility to take care of this (by installing signal handlers etc.). We can do what we need to from the rlbox side while wasm2c can say it doesn't promote explicit non-conformance

[shravanrn]

@keithw Given the discussion in #2357, I think we can now retry landing this. Please let me know your thoughts

[keithw]

Go for it!