Xila

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Virtual machine ​

Xila's WebAssembly runtime lives in executables/wasm and uses the Wasmi interpreter. The host feature means Xila hosts guest programs; it also works when Xila itself runs in a browser. The previous WAMR integration and Runtime::execute API have been removed.

Responsibilities and boundaries ​

  • Load a regular file from Xila's VFS and validate its WebAssembly module.
  • Create a Wasmi engine, linker, module, and store for each execution.
  • Register WASI Preview 1 imports and optional Xila graphics imports.
  • Invoke _start: () -> (), or __install: () -> () with --install.
  • Cooperatively yield, suspend, and resume the guest without holding guest-memory borrows across an await.

This layer does not provide full WASI coverage or direct hardware access. Its capabilities come from the caller's ExecutableContext.

Internal architecture ​

  • host/main.rs: argument parsing, VFS loading, engine/linker construction, and entrypoint selection.
  • host/store.rs: per-execution GlobalStore holding the executable context, pending suspension, WASI state, and optional graphics state.
  • host/execution.rs: resumable Wasmi calls, fuel replenishment, yield handling, clock waits, and exit/error propagation.
  • host/wasi/: file/directory descriptors, environment and arguments, clocks, random data, process exit, and supported polling imports.
  • host/translation/: checked borrowed guest-memory access and pointer/word-width conversion.
  • host/graphics/: runtime-independent dispatch, object handles, and marshalling, plus a thin Wasmi adapter.

Lifecycle and execution model ​

  1. Read guest bytes and create a fuel-enabled engine and module.
  2. Build a store from Standard::context; install stdin/stdout/stderr as descriptors 0/1/2 and preopen / if available.
  3. Copy the task environment and use the module path as the guest argument.
  4. Register WASI and optional graphics imports, instantiate the module, then select a typed entrypoint.
  5. Execute resumably; on fuel exhaustion, yield and replenish fuel. sched_yield suspends locally; supported poll_oneoff clock calls wait asynchronously before resuming.
  6. Propagate exit status or traps and tear down execution state, including owned graphics windows.

Scheduling and limits ​

  • The instruction quantum controls fuel replenishment between yields rather than a total lifetime instruction budget.
  • Clock polling supports realtime/startup clocks with relative or absolute deadlines. File-descriptor polling and unsupported clocks return errors.
  • Startup-clock behavior follows Xila's time manager and its driver; it is not a separate hardware monotonic source.
  • Suspension in a WebAssembly start section is unsupported. WASI command guests should use exported _start.
  • The stack-size option is parsed but is not applied by the runtime.
  • memory_32 is the default guest-word width; memory_64 selects the alternate translation configuration. Calculator remains a wasm32 guest.
  • Graphics capabilities cover the supported subset documented in Bindings; enabling graphics does not provide every LVGL API.

The runtime reference is the authoritative lookup page for option defaults and polling capacities.

References / See also ​