Links

• Required Services
• Extended Services
• Wasm C-ABI
• Wasm Linear Stack Description
• Example of WebAssembly inline assembly
• Example of WebAssembly .s files

Rationale

• Choice: <an APEX integer type> -> APEX_LONG_INTEGER Reason: These placeholders are only used for *_ID_TYPE. All of these IDs are only ever handed out by the OS. By picking the largest possible type available (64-bit integer), we ensure that we are compatible with any possible OS, as we can store any possible ID. For an OS that chooses a 32-bit integer, the upper bits just remain untouched.
• Choice: import the linear memory (via --import-memory linker flag) Reason: Each partition has multiple processes, which are guaranteed to have a shared address space (ARINC 653 P1-5 chapter 2.3.2). The only way to achieve this is if they have shared linear memory. To cause that, they all need to import the linear memory.
• Choice: export the function table (via --export-table linker flag) Reason: In order for the CREATE_PROCESS call to succeed, the host environment needs to be able to call a guest environment function identified via an index into said table. Exporting the table ensures that the funcref table is accessible from the host environment.
• Choice: Do not use __externref_t for function pointers, e.g. the ENTRY_POINT argument in the CREATE_ERROR_HANDLER function. Reason: __externref_t is not representable in Linear Memory. Hence, it can not become the field of a struct. However, the PROCESS_ATTRIBUTE_TYPE struct comprises an ENTRY_POINT field holding a function pointer. As __externref_t can not be used there, it is necessary to expose the table for function pointers. Therefore, any use of __externref_t shall be avoided, in order to keep all function pointer representations consistent.
• Choice: Use __wasm__ preprocessor #define to conditionally annotate official APEX header functions with import_module & import_name attributes. Reason: Clang is the sole compiler, that is capable to compile C to Wasm reasonably. Heaving two headers, one without and one with Wasm specific annotations, is unfavorable.

Legal Matter

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License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT License (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

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