I’m looking to write a tool that aims to convert debug symbols of one format to another format that’s compatible for use under GDB. This seems like a tedious and potentially complex project so I’m not exactly sure how to tackling it.
Intially I’m aiming to convert the Turbo Debug Symbol table(TDS) emitted from borland compilers into something like stabs or dwarf format(seems like dwarf is prefer from my research). But ideally I want to design my tool to be easy enough to extend so it could convert other formats too later on. e.g. codeview4 or maybe even pdb.
My primary motivation for creating this are:
- Interoperability. If I can convert a foreign debug format into a form gdb can work with then source-level debugging would be possible on binaries compiled from another compiler other than gcc. This means any frontend debugging interface that uses gdb as a backend will work as well.
- No other tools exist. I did a google searching around for similar tools and the closest I’ve found is tds2dbg. But it doesn’t quite do what I’m looking for.
What I have to work with at the moment:
- I already have a debug hook API that can understand the TDS debug format. I can use that to help me get at the needed information from the source format I’m converting from.
- For the scope of this project, I’m mainly interested in getting this to work under the win32 environment. Other platforms and tools I’m not really concerned about.
- The target dwarf debug format I’m converting to. This one I’m really not familiar with at all. I have used gcc ported compilers like MinGW before and debugged them with gdb with the dwarf format. But I don’t have any idea how this format is implemented on windows.
The last point is the one I’m concerned about. I’m reading through the dwarf spec documentation but I find I’m having trouble really understanding and comprehending how it works. There’s so much detail in there but at the same time it doesn’t have any details about how dwarf gets implemented on object files and image files on a platform that doesn’t use ELF natively — namely the PE-COFF format that windows uses. The documentation is also a very dry read, long sentences make it hard to understand and diagrams and illustrations are sparse. I came across an API called libDwarf that should take most of the parsing work out of interpreting dwarf. The problem is I’m still trying to get it to build and I don’t know yet how it will work out.
I haven’t written any code yet since I don’t fully understand what it is I need to build. I have a feeling the biggest hurtle will be figuring out how to work with dwarf due to it’s complexity. Googling for information on how dwarf works under windows hasn’t turned up anything helpful either. Like for example, there’s no information about the ‘glue’ code that’s needed to contain dwarf within a PE executable image file. How are the dwarf sections exactly layed out? Are there any header information for each section? GDB clearly doesn’t just take a ‘raw’ dwarf debug file and use it as is. So what kind of format does gdb expect the debug file to be in for it to be able to work with it?
My question is, how can I start on such a project? More importantly, where can I turn to for help when I inevitably get stuck on a problem?
You are asking several questions here 🙂
I think you are heading in the right direction, using libdwarf.
BUT, have you taken a look at objcopy to see if this tool can do some of the work for you? It probably doesn’t support borland, pdb or codeview4, but it might be worth looking into. (Another approach may be to extend objcopy to support the formats you are trying to convert between.)
I have used the dwarf-discuss mailing list sometimes when I have become stuck.
http://lists.dwarfstd.org/listinfo.cgi/dwarf-discuss-dwarfstd.org
As for the questions on dwarf, split them into separate questions and I will do my best to
answer them. 🙂