Regulus

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Runtime memory management ​

Runtime memory management is implemented in the WebAssembly runtime prelude. The prelude is emitted only for modules that need managed values or runtime helpers.

Current model ​

Regulus uses a resettable bump arena in linear memory.

  • Static managed objects are emitted as data segments before the dynamic heap.
  • $__heap is the next dynamic allocation offset.
  • __alloc aligns each request to 8 bytes.
  • Allocation advances the heap pointer and never frees individual objects.
  • Objects are non-moving until the Wasm instance is reset or a future explicit arena reset runs.

This keeps allocation small and makes raw i32 managed-value pointers stable for generated code and Wasmtime tests.

Growth and failure ​

Every allocator path must call __alloc or a helper that delegates to it. __alloc checks whether the aligned allocation end fits in current linear memory. If it does not fit, it computes the required page count and calls memory.grow.

Allocation fails when:

  • size arithmetic overflows,
  • the required page count cannot be represented, or
  • memory.grow returns -1.

Allocation failure records a tag-10 panic payload through __last_panic. The payload reason tag is 1; slot 0 is the requested allocation size and slot 1 is the heap pointer before allocation.

Host ownership ​

Managed pointers exported to a host are borrowed. The guest runtime owns the object. A borrowed pointer remains stable after the exporting call returns, but the host must not retain it across Wasm instance reset or a future arena reset.

Browser adapters must refresh typed array views after memory growth. Wasmtime tests can read the exported memory directly after each call.

Deferred work ​

Reference counting and tracing garbage collection are deferred. Either design needs complete root metadata, stack and local tracking, clear host ownership rules, and tests for pointer lifetime across host calls.

See also: