PDB support in LLVM

Is making PDB files for corresponding IR supported in LLVM latest version?

After some searching I see llvm-pdbdump, but I want to annotate the IR with debug information so that when I write bitcode it has pdb information.

I’ve heard of CodeView, but it seems to be only for line information. I want variable values also.

I would be ok to use DWARF if Visual Studio could understand it using LLDB but I don’t know how to do that or if it is support.

I would also be ok to write DWARF and then convert to PDB if such is possible.

How can I achieve this?

Is making PDB files for corresponding IR supported in LLVM latest version?

Not today.

After some searching I see llvm-pdbdump, but I want to annotate the IR with debug information so that when I write bitcode it has pdb information.

I’ve heard of CodeView, but it seems to be only for line information. I want variable values also.

I would be ok to use DWARF if Visual Studio could understand it using LLDB but I don’t know how to do that or if it is support.

Zach (CC-ed) and others are actively working on making LLDB work well on Windows, including reading DWARF debug information on Windows and potentially integration with Visual Studio (although I think that is further away at the moment). However, further discussion might be better on the LLDB mailing lists.

I would also be ok to write DWARF and then convert to PDB if such is possible.

How can I achieve this?

Personally, I suspect the best way to do this is to write DWARF and get LLDB into your workflow (either directly with the command line or in the IDE). That at least is the path others are currently pursuing.

Is making PDB files for corresponding IR supported in LLVM latest version?

Not today.

After some searching I see llvm-pdbdump, but I want to annotate the IR with debug information so that when I write bitcode it has pdb information.

I’ve heard of CodeView, but it seems to be only for line information. I want variable values also.

I would be ok to use DWARF if Visual Studio could understand it using LLDB but I don’t know how to do that or if it is support.

Zach (CC-ed) and others are actively working on making LLDB work well on Windows, including reading DWARF debug information on Windows and potentially integration with Visual Studio (although I think that is further away at the moment). However, further discussion might be better on the LLDB mailing lists.

It’s worth pointing out that CodeView is not only for line information. It’s for everything. It’s just that LLVM currently only understands a subset of CodeView record types related to line information.

Moving to lldb-dev per suggestion.

Using Visual Studio is only criteria for us. It could be DWARF or PDB.

But I need to implement this soon (4-5 weeks from now). What do you recommend?

Zachary do you also suggest using LLDB on Windows?

It sounds like if you have a time frame of 4-5 weeks, you’ve got a tall order cut out for yourself. I don’t want to say impossible, but… that’s pretty rough.

I think you’ve got two options:

  1. Try to figure out how to emit PDB. The format is undocumented, so you’re kind of on your own here.
  2. Try to figure out how to get Visual Studio to understand DWARF. Visual Studio has a reasonably rich extensibility model which is also not very well documented, so you’re probably on your own here as well. You may want to have a look at PythonTools for Visual Studio. It’s entirely open source and adds Python debugging to Visual Studio. Obviously you don’t need to be able to debug Python, but it’s the best source of documentation I know of for extending Visual Studio in this kind of way so maybe it will help. If you end up doing this, it would be great if you could try to upstream it back to LLDB. Visual Studio integration with LLDB would be nice to have.

You could try extending the codeview and then relying on the ms linker to emit a pdb from it (last time I checked it converts on the fly - this may have changed recently, and what it converts may not be fully featured).

The Debug Engine extensibility for visual studio is, as Zach says, not well documented at all. Despite that, in the past I have had LLDB chatting in a limited way to visual studio. It was incredibly messy, and the way I chose to do it was go from Visual Studio → c# → c++/CLI → C++ lldb api. Don’t do it that way if you attempt it: Create lldb C# bindings instead and go that direction. I’ve been looking at that lately but it’s a side project so cant be relied on if you need it quickly.

As for the time frame, 4-5 weeks isn’t going to get far given the lack of documentation. The debug engine samples don’t go far enough in terms of requiring a native C++ environment.

Colin

Btw the python tools project doesn’t use Dbgeng extensibility model, it’s a newer richer extensibility framework that is even less documented (most people probably wouldn’t even know it exists) but much more powerful. And it’s all in managed code, so you get the c# stuff for free.

But still, 4-5 weeks seems very aggressive

I think that’s what I used. Hence why I want lldb C# bindings! But yeah. Horridly underdocumented.

There seems to be an DWARF to PDB converter here:

https://github.com/rainers/cv2pdb

Not sure how good it is or what the license looks like...

FYI if you're still looking, Microsoft published the source code for
the MIEngine that is essentially a Visual Studio Debugger Extension
that implements the Core Debug Interfaces
(Core Interfaces - Visual Studio 2015 | Microsoft Docs)

It can talk to LLDB and GDB.

https://github.com/Microsoft/MIEngine

I don't think MIEngine will help with support for the PDB debugging format. It allows Visual Studio to use lldb to drive a Visual Studio debugging session, but in this mode all the symbol & debug reading work is off-loaded to lldb.

It is possible to do a hybrid model where the low level debugger doesn't do symbol reading, and some other driver tells it "what it needs to know". For instance, this is the way the OS X port of MetroWerks' CodeWarrior was implemented. But that was a real pain to support. There are times particularly down in the bowels of the stepping machinery where you really need symbol information. This never worked really well.

Jim

Should have clarified, the OP mentions in the thread that they doesn’t specifically care about PDB generation as much as being able to use Visual Studio with LLDB.

If you’re still looking for it, we at Xamarin have recently created some C# bindings for LLDB. We also built a proof of concept native debugger addin for Xamarin Studio.

It’s all open source, the bindings themselves are available here: https://github.com/tritao/LLDBSharp

Let me know if you find them useful for need some help in generating the bindings for other ABIs (Windows).

the lldb-mi plugin for Visual Studio they’ve announced only enables (afaik) debugging of mobile devices from within Visual Studio. The code running on these mobile devices, however, was never compiled with MSVC to begin with, and thus does not have PDB debug information, it uses DWARF. So it’s kind of orthogonal to PDB and won’t really help I think.

It is not restricted to mobile devices.

But as I said, the OP states he cares about using Visual Studio to
drive LLDB and not necessarily PDB output.

I was replying to that intent, didn't mean to confuse the thread about
PDB creation.