Hi,

When we run cargo xbuild --release ... --target x86_64-kernel.json, the memcpy being compiled is just a simple un-optimized for-loop. Looking at the source code, I think xargo builds sysroot crates in release mode by default.

I think there's something else in our settings that prevents xargo from building an optimized compiler_builtins but I am not sure what am I missing. We borrowed some of the setups, including the target.json, from Writing an OS in Rust.