Add stack overflow checks in wasm backend?

[kripken]

In fastcomp, ASSERTIONS=1 adds stack overflow checks. The wasm backend doesn't have this, but maybe it's useful and we should add it?

[VirtualTim]

My understanding is that the UBSan work @quantum5 has been doing is kind of a better version of this sort of stuff.
Maybe it's better to just use that instead? The only downside I can think of is that it currently doesn't work with threads.

[kripken]

Ah, good point @VirtualTim! Yes, I think UBSan or ASan should handle this - @quantum5 can you confirm? If so then I agree we should indeed just point people to that.

[quantum5]

ASan is not designed to catch stack overflows, just like how it's not designed to catch null deferences. On native platforms, that is done by putting invalid pages. But I am sure ASan can be modified to do so on Emscripten, just like it has been modified to catch null deferences.

I think we can just overallocate, say 64 KB of stack, and poison the shadow memory for it.

The thread part will have to wait until #9076, of course.

[quantum5]

ASan doesn't seem to work too reliably for this purpose.

I think a binaryen pass that ensures the stack pointer does not dip below the end of the stack is simpler and makes more sense.

[kripken]

The test for this for the wasm backend, test_stack_overflow_check, is still disabled. It looks like it can't be enabled, as the code so far just checks if the new value of the stack is above the lower limit. However, it is an unsigned comparison, so if we try to allocate so much that it wraps around into a huge amount, it looks higher than the limit, and passes the check, which fails the test.