Emit debug info

[jyn514]

Related to #16, but at the object file level instead of assembly level: We should emit debug info for the binary we emit.

I think https://docs.rs/cranelift-frontend/0.51.0/cranelift_frontend/struct.FunctionBuilder.html?search=#method.set_srcloc is the API we want?

[jyn514]

This looks helpful: bjorn3/rustc_codegen_cranelift@5873127

[philipc]

Currently cranelift only provides minimal debuginfo support:

• it allows attaching an opaque srcloc to the IR, and preserves these through to the generated code
• it tracks frame layout (see Track frame layout changes. (cont.d) bytecodealliance/cranelift#1204)

But for both of these, it is up to the user to then generate the debuginfo. For examples of doing that, rustc_codegen_cranelift can generate .debug_line information from the srcloc as you have seen (as well as incomplete .debug_info support), and bytecodealliance/cranelift#902 can generate .eh_frame information from the frame layout. Both of these use https://github.com/gimli-rs/gimli to do the writing.

Eventually there will probably be something that makes this all easier for users, but for now it's a bit experimental.

[jyn514]

@philipc thanks for the tips! For now, this is fairly low on the todo-list, so I'm fine with waiting a little to see if a better API pops up. If not, I may get to it in a month or so.

Currently, the debug info is mostly so I can debug my own bad codegen, since no one is using my compiler for their own projects yet.