This is a copied version of libcore with various pieces disabled to work around limitations in the current AVR backend.
The goal of this library is to no longer exist. The issues are intended to track each piece of libcore that AVR cannot currently support.
The version of this library needs to match the original Rust commit that your compiler is built from. This code is from rust-lang/rust@26015da0.
You can add it to your xargo configuration file (Xargo.toml) as such:
[target.avr-atmega328p.dependencies]
core = { git = "https://github.com/avr-rust/libcore", branch = "rust-26015da0" }
Check out the issues to find a piece of missing functionality that interests you. Revert the corresponding commit and build the new libcore to ensure that there's still a code generation problem. Then start tracing through the LLVM code to figure out what needs to change!