Risto (Sep 01 2020 at 12:54): Risto (Sep 01 2020 at 12:54):I am trying to use wasmtime from my own program to run a module that opens a file for reading. The file is in same folder with the runtime.
I have tried setting up WASI and the linker in the following manner after which I run the Wasm module.
let wasi = Wasi::new(&store, WasiCtx::new(std::env::args()).expect("Wasi Error"));
wasi.add_to_linker(&mut linker)?;
let main_module = Module::from_file(store.engine(), "./example_main.wasm")?;
let main_instance = linker.instantiate(&main_module)?;
linker.instance("example_main", &main_instance)?;
linker.alias("example_main", "env")?;
However, calling fopen in the module returns NULL and perror prints a message saying "Operation not permitted".
The same code in C works fine, so file permissions are unlikely the cause. The file also has 777 permissions.
I would assume that I have some permissions missing from WASI to allow it to access files.
I tried passing different switches to the program ./example --dir=. --dir=absolute/path/to/example/folder ./example -- --dir=. --dir=absolute/path/to/example/folder, but none change the error message.
Pointers to where the issue could be are appreciated.
Risto (Sep 01 2020 at 13:49):Tried to use fopen with wasmtime-cli too, but it has the same error, so the problem isnt specific to my code either.
bjorn3 (Sep 01 2020 at 14:07):You need to use WasiCtxBuilder and call preopened_dir I think. WasiCtx::new takes the arguments to be passed to the wasm module, not arguments to customize WasiCtx.
Risto (Sep 01 2020 at 14:10):It seems that the issue might be with the module itself. It was built with emscripten.
Running the examples from here worked fine, unless compiled with emscripten https://github.com/bytecodealliance/wasmtime/blob/main/docs/WASI-tutorial.md#executing-in-wasmtime-runtime
Risto (Sep 01 2020 at 16:23):Posted an issue about it here: https://github.com/emscripten-core/emscripten/issues/12094
Last updated: Dec 06 2025 at 06:05 UTC