Initial 'design' for aggregating verification errors in llvm-dwarfdump

[kevinfrei]

I'm not done (the final report is hideous, and I haven't gone through every error just yet) but I wanted to get any feedback on this particular design for how to aggregate errors in the verification pass.

[clayborg]

I was thinking that each place that is throwing or printing an error would have a category string, and a detail string. So if we had existing code like this:

error() << "Compilation unit type (" << dwarf::UnitTypeString(UnitType)
            << ") and root DIE (" << dwarf::TagString(Die.getTag())
            << ") do not match.\n";

If we add an error reporting function somewhere, maybe like this:

DWARFVerifier::reportError(
    llvm::StringRef Category, 
    std::function<void(raw_ostream &Out)> DetailCallback);

This allows us to change the above code to this:

reportError("Compilation unit type mismatch", // Category
                     [&](raw_ostream &Out) {
                         Out << "Compilation unit type (" << dwarf::UnitTypeString(UnitType)
                                << ") and root DIE (" << dwarf::TagString(Die.getTag())
                                << ") do not match.\n";
                     });

The cool thing about this, is in the reportError(...) function, we don't need to call the DetailCallback if we are running in summary mode. In summary mode we just end up incrementing a counter for each Category string. But when running in normal mode, we can and will call the DetailCallback (which everyone will just make a lambda for). This will allow summary mode to be really fast as it won't cause a ton of output to be generated. It also allows each detail callback to do expensive logging.

[clayborg]

It would be nice to report the Unit DIE offset in this message? This could be a follow up patch though.

[clayborg]

Would be nice to have the offset of the skeleton unit DIE in the detail. Again, if we are looking to match older output, we can do this later.

Another idea is to allow an offset to be specified as a parameter to the Report(...) function. It would be kind of cool to be able to report the count and category along with any values for each error. If we specify --verbose --summary then it could print out something like:

1234 "Skeleton CU has children" [0x1000, 0x2000, 0x3000]

Any offsets specified in a report could be displayed to show where these errors happened. So in this case if we did this we could add a parameter to the end:

ErrorCategory.Report("Skeleton CU has children", [&]() {
      error() << "Skeleton compilation unit has children.\n";
  }, Die.getOffset()); // <<< Offset as the third parameter.

Then each category could store a vector<uint64_t> values and report them in verbose mode?

[clayborg]

Both dump(OS) methods need to go in lambda