compiler-builtins VS cargo-wasi

I don't know which symbols are missing, haven't done anything on the llvm level. But I had the same problems creating a no-std no-libc application, if you add https://github.com/rust-lang/compiler-builtins as a dependency you should get all the symbols you need, std uses the same but if you want to use it outside of std you'll need nightly since it uses a lot a nightly features. It might apply to your case as well.

Ah, I see - you might be hitting https://github.com/rust-lang/compiler-builtins/issues/347.

There's a PR to the compiler-builtins crate which the rust implementation is based on.

I'm glad to inform y'all that after a year, the infamous LLVM ERROR: Not supported instr bug¹ has been finally fixed and today's nightly can compile for AVR back again! 😎

Then, some of the non-trivial things that are needed are already implemented and maintained in other crates, like memcpy and friends in compiler-builtins, all the math routines in libm and malloc in dlmalloc.

3.Use scons to compile, if errors jumped on link up, find the solution on its official Github.

There are many options, but what worked best for me is compiling with cargo-wasi and loading the resulting Wasm file with browser_wasi_shim. Using wasm32-wasi instead of wasm32-unknown-unknown requires a bit more work (the communication with JS has to be set up manually), but gives the flexibility of having just a Wasm file that can be dropped in and loaded dynamically. (There's wit-bindgen for generating wrapping code according to an interface definition but I didn't have much success with it.)

I use cargo-wasi to build it: