This code works currently on ArchLinux (and Ubuntu - see CI):
$ yay -S clang lld wasi-libc wasi-compiler-rt libwasmtime iwasm
iwasm PKGBUILD must be patched to not strip the static library. See https://aur.archlinux.org/packages/iwasm

Content:
The given code showcases that a Wasmtime and WebAssembly Micro Runtime (WAMR) can support ARINC653 APEX interfaces as host functions. The PoC shall also proof, that it could work on Little Endian as well as Big Endian architectures (such as PowerPC still represented in avionics). There are a few caveats why ARINC653 APEX interfaces can't be 100% compliant to the WebAssembly standard, however the main language C (and C++) is supported and Ada should be supportable:

1. APEX interfaces defined in WIT will not generate the proper APEX standardised function defintion through wit-bindgen. Thus, the APEX interface is exposed as a plain C header, where to-be-Wasm-ised source code can be directly compiled against.
2. CREATE_PROCESS() and CREATE_ERROR_HANDLER() can't comply to the WebAssembly standard, as they pass a function pointer SYSTEM_ADDRESS_TYPE.
3. WebAssembly defines that values returned are passed through a host functions return .... Meaning, function parameteres are 'just' input. However, the APEX interfaces all use plain pointers as function parameters to return content.

Again, as long as C, C++, Ada are the main languages, above points should be no worry.

Open Topics:

1. Fix NixOS CI builds (currently this code works on Ubuntu and ArchLinux)
2. Use better threading: DLR-FT/arinc653-wasm@main...dev/add-wasm-apex-proc-alloc

Choosing WebAssembly runtime
The compilation will create a bin folder. Change the symlink from p_wasmtime to p_wamr if WAMR shall be employed.

WebAssembly Specification

https://www.w3.org/TR/wasm-core-2/#concepts%E2%91%A0

"Each function takes a sequence of values as parameters and returns a sequence of values as results."

https://www.w3.org/TR/wasm-core-2/#function-instances%E2%91%A0

"A host function is a function expressed outside WebAssembly but passed to a module as an import. The definition and behavior of host functions are outside the scope of this specification."

https://www.w3.org/TR/wasm-core-2/#functions%E2%91%A4