Stream: wasmtime

Topic: Setting Memory Reservation of Compiled Module

Lukas (Jun 19 2025 at 07:35):

I'm currently trying to run wasmtime in a no_std environment with limited memory on RISC-V. To achieve that, I compile wasm binaries the following way:

wasmtime compile \
                                --target riscv64gc-unknown-none-elf \
                                 -C collector=null \
                                 -W threads=n \
                                 -W component-model=n \
                                 -W gc=n \
                                 -W memory64=n \
                                 my-app.wasm

I only have one memory section in my-app.wasm with the following layout: (memory (;0;) 17 20).

I then run my application like this:

        let mut config = Config::new();
        config.memory_reservation(4_294_967_296);
        config.memory_guard_size(33554432);
        config.signals_based_traps(true);
        config.memory_init_cow(true);
        config.wasm_memory64(false);

        let engine = match Engine::new(&config) {
        // ...
        match Module::deserialize(&engine, file_buffer) {
        // ...

As soon as my cwasm binary has a memory section, the linker seems to try to allocate 4GB of memory, which will not work on my machine - and which shouldn't be necessary.

However, if I set config.memory_reservation to anything other than 4GB, I get an error while building the module: Module was compiled with a memory reservation of '4294967296' but '33554432' is expected for the host

I don't see any way to compile the module with a different memory reservation, -W max-memory-size=<value> doesn't seem to have an impact either.

Is there a solution to this problem?

Last updated: Dec 06 2025 at 06:05 UTC