Emit windows-specific debug info

[brson]

LLVM supports a simple windows-specific debug info containing just line numbers, that works correctly in the MS debugger. @michaelwoerister knows the details.

[michaelwoerister]

The relevant information can be found at http://clang.llvm.org/docs/MSVCCompatibility.html:

Clang emits both CodeView line tables (similar to what MSVC emits when given the /Z7 flag) and DWARF debug information into the object file. Microsoft’s link.exe will transform the CodeView line tables into a PDB, enabling stack traces in all modern Windows debuggers. Clang does not emit any CodeView-compatible type info or description of variable layout.

We should try and support this functionality also in rustc.

[retep998]

This depends on adding support for rustc using link.exe.

[michaelwoerister]

Yes, if you don't want to do your linking manually. I agree that if we say that we support this type of debuginfo, we should also make it as ergonomic as possible.

[Manishearth]

Perhaps we can copy the .NET implementation if we want full PDB?

https://github.com/dotnet/roslyn/blob/6f35e33694ac042a93195200bf0a317826c0388f/src/Compilers/Core/Portable/PEWriter/PdbWriter.cs

https://github.com/dotnet/roslyn/tree/b6484300dfafb43af0c27e542ec457a7583e1aa8/src/Test/PdbUtilities

https://github.com/dotnet/coreclr/blob/cbf46fb0b6a0b209ed1caf4a680910b383e68cba/src/vm/compile.cpp

This probably is something LLVM needs to support.

[Manishearth]

cc @metajack @larsberg

[alexcrichton]

Assigning to @michaelwoerister, this is coming more relevant now that we have initial MSVC support!

[jrmuizel]

FWIW, I have the beginnings of a LLVM patch for adding x86-32 FPO information for unwinding.

[michaelwoerister]

Quick update: It seems that LLVM on Windows will already emit CodeView line tables alongside DWARF if debuginfo is enabled. We just have to instruct link.exe to convert these into a PDB file, using the /DEBUG option. In a minimal proof of concept I was able to compile a small Rust program and step through it using WinDbg.

[Manishearth]

Would this solve the problem? Or will we still need to rig something up for printing local vars &c?

[michaelwoerister]

As far as I know, it should bring us on the same level as Clang as far as PDB debuginfo is concerned. Variable and type information just isn't supported by LLVM yet.