Write down where all the unwind/backtrace code is

Location

It's in at least three different locations, depending on how you count! That's the problem!

Summary

Internal-facing documentation, mostly?

The problem is this, essentially: we have our internal unwinding/backtrace-related code in

• library/backtrace
• library/panic_abort
• library/panic_unwind
• library/std/src/sys/personality
• library/unwind

And the interrelationships are not so clean and obvious that you can simply follow imports, because sometimes the bridge is performed by raw compiler magic! Because, in fact, you do generally need compiler support to get a decent backtrace or to unwind correctly! So arguably I could also mention files like:

• rustc_codegen_ssa/src/mir/block.rs

Understanding all of these should not be the exclusive province of a few wizened sages of the dark arts. They should all backref to an index that tracks them. And if any can be eliminated and merged into others without causing horrid problems, they should be.

Start by inventorying the unwind and backtrace code in library/backtrace, library/panic_abort, library/panic_unwind, library/std/src/sys/personality, library/unwind, and rustc_codegen_ssa/src/mir/block.rs. Document how these locations relate, including compiler-magic bridges, in an index with backreferences; done means a newcomer can find and understand each relevant area.