threads: add function validation of atomics

[anuraaga]

No description provided.

[mathetake]

I slightly remember that memory must have min==max, but where is it validated?

[anuraaga]

@mathetake Hmm, don't think I've seen that anywhere. For example in libpgquery wasm, memory looks like this

(memory (;0;) 15 65536 shared)

[mathetake]

aha ok

[mathetake]

then what happens when growing memory (changing the base address would be dangerous I guess when multiple threads are executing load/store?)

[anuraaga]

@mathetake Yup you're right. We discussed a bit but basically the only way to support it, without allocating tons of memory up front, is to use mmap. I think I need to clean up the implementation a bit before sending the PR for here, but currently it looks like this

https://github.com/wasilibs/wazerox/blob/main/internal/wasm/memory.go#L74

Will it be ok?

[mathetake]

yeah looks good provided the behavior is well-documented on the API to toggle threads instructions. IIRC mmap itself doesn't immediately allocate physical pages immediately so it makes sense

[ncruces]

I wonder, do tests pass on 32-bit platforms, with mmaping 65536 pages (4GB)?

[anuraaga]

@ncruces Probably not, though I haven't tried it. To clarify it's not really engine or compiler related but a flag set by the user when building

https://github.com/wasilibs/go-pgquery/blob/main/buildtools/wasm/Dockerfile#L6

I copied that number from wasmer but I think I'll lower it to 2GB to best effort support 32-bit host.