[PATCH] D16697: Updating .debug_line section version information to match DWARF version.

[Robinson, Paul via llvm-commits]

> > There is now a public bot that runs the LLDB testsuite on Darwin
> (http://lab.llvm.org:8080/green/job/LLDB/) so you’ll find out immediately
> :-)
> > LLDB can be fixed, I’m not too worried about it.
> >
> > There are, however, also DWARF consumers that are not debuggers that
> will read the line table, such as CoreSymbolication (atos(1)). I’ll
> investigate whether it can digest the newer version and follow up here.
> 
> CoreSymbolication (which produces symbolicated crash traces) does not yet
> support the version 4 header. It would be great if we could have a
> separate option to control the version of the line table independently
> from the debug info version. We are in the process of making DWARF 4 the
> default on Darwin and being able to upgrade the debug info independently
> from the line table independently would make staging this a lot easier.

Adrian, would an MC command-line option be sufficient for this, or do you
need something plumbed all the way down from the Clang driver?  Last time
I talked to Katya she was not sure what would work for you.  My thought
would be along the lines of:
  start with general DWARF version
  if something was explicitly requested
    use it
  elif Darwin
    clamp it to 3
where "explicitly requested" would be an MCDwarf specific option.
So, you can use it directly from something like llc, and also possible
to use from Clang driver but less conveniently (with -mllvm). Then when
Darwin is fully v4-ready, you can rip out the extra option.

How does that sound?
Thanks
--paulr

> 
> -- adrian
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