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

[Adrian Prantl via llvm-commits]

> On Feb 12, 2016, at 5:07 PM, Robinson, Paul <Paul_Robinson at playstation.sony.com> wrote:
> 
>>> 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

Is there a precedent for making target-platform-specific decisions like this in the backend?
If this is common practice, I’m fine with doing it this way. Otherwise a cc1 option that is set by the driver seems to be a bit cleaner (less magic). There’s no need to expose it as a driver option, though.


-- adrian
> 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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