I'm trying to understand where i can find info on the the start lang item and i cant seem to find it anywhere
A great starting point written by Manish if you haven't read it: Rust Tidbits: What Is a Lang Item? - In Pursuit of Laziness
Update: that article illuminates the functionality of common lang items, specifically for the start lang item you're interested in:
We’ve already seen the start lang item (std) being used in our minimal example program. This function is basically where you find Rust’s “runtime”: it gets called with a pointer to main and the command line arguments, it sets up the “runtime”, calls main, and tears down anything it needs to. Rust has a C-like minimal runtime, so the actual libstd definition doesn’t do much. But you theoretically could stick a very heavy runtime initialization routine here.
Short and formal doc of lang items: Lang Items - Guide to Rustc Development