[clang] [llvm] [clang][DebugInfo] Add symbol for debugger with VTable information. (PR #130255)

[David Blaikie via llvm-commits]

dwblaikie wrote:

> It would be better if we could go from the vtable pointer straight to the right type DIE, but I don't think we can do that without inventing a new sort of an accelerator table (which I guess we don't have an appetite for).

yeah, data address lookup (as opposed to code address lookup) is somewhat of a gap in DWARF at the moment. In /theory/ aranges held data and code addresses, but GCC only produced code addresses (LLVM produced data and code addresses, but didn't produce aranges by default because they were redundant (at least when ignoring data) with ranges)... 

We could revisit that in some way - it (ranges or aranges) is not a lookup table, but it does at least give quick per-CU ranges. For DWARFv5 output, if you know only indexed addresses are being used (either becuase it's Split DWARF, or by scanning the abbrevs, maybe?) maybe you can still get a per-CU "which CU covers this vtable" query that's pretty quick (not sure if DWARF compression tools like dwz would make that more difficult because the indexed addr entry might not point straight to the start of the vtable - an offset to the vtable might be used somehow (like the new addr+offset form in DWARFv6)?)

But, yeah, I wouldn't mind hearing more about lldb's needs/preferences/hopes/dreams for this feature so we might get a design that's more portable at least between SCE and LLDB. (bonus points if anyone's got GDB's needs in mind - perhaps @tromey might be able to lend us some insight as to how GDB does things and what they might be inclined to use/support to improve this feature area)

https://github.com/llvm/llvm-project/pull/130255