Stream: wasmtime

Topic: neato little thing using wasmtime

Ralph (Apr 27 2026 at 07:49):

https://abacusnoir.com/2026/04/18/zero-copy-gpu-inference-from-webassembly-on-apple-silicon/

Link 3: Wasmtime lets you bring your own allocator. Wasmtime's MemoryCreator trait lets you control how linear memory is allocated. Instead of letting Wasmtime call mmap internally, you provide the backing memory yourself. I implement MemoryCreator to return our own mmap region, and Wasmtime's memory.data_ptr() returns exactly the pointer I handed it. The Wasm module reads and writes through Wasmtime's memory API; the GPU reads and writes through the Metal buffer; both are operating on the same bytes.

The composition: allocate an mmap region, hand it to both Wasmtime (as the actor's linear memory) and Metal (as a GPU buffer). The Wasm module writes data at known offsets, the GPU computes on it in place, and the results appear in the module's linear memory with no copies and no explicit data transfer.

Ralph (Apr 27 2026 at 07:58):

That said, it sure looks to me like this dumps some boundaries we really want.

Ralph (Apr 27 2026 at 08:06):

https://thepixelspulse.com/posts/zero-copy-wasm-apple-silicon-gpu-inference/ for a shoutout to the component model: "The Future: WebAssembly Component Model and True Zero-Copy"

bjorn3 (Apr 27 2026 at 13:25):

Wouldn't be too surprised if that allowed a sandbox escape if the linear memory isn't marked as shared memory on the wasm side.

Last updated: May 03 2026 at 22:13 UTC