compiler-builtins VS avr-device

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.

Also note that some libraries in the ecosystem might still use a feature called llvm_asm that was removed from rustc in 2021, so those crates might need a while to migrate to the newer asm syntax (this feature is used to provide an inline AVR assembly, e.g. to implement a cycle-accurate delay); so far I've got patches merged to https://github.com/Rahix/avr-hal & https://github.com/Rahix/avr-device :-)

Take a look at the avr-device crate, it also explains how to add a new controller and how to get to the svd files.