Re: DWARF5 and .gdb_index/.debug_names

On 8/30/20 7:18 PM, Mark Wielaard wrote:
> Hi,
> 
> Last week we had a DWARF BoF at the virtual GNU tools cauldron.
> Notes have been posted to the gcc wiki:
> https://gcc.gnu.org/wiki/LPC2020NotesDWARF
> 
> I would like to try to make DWARF5 the default for GCC11 and have been
> trying to fix any issues I could find. Testing gdb went pretty well.
> There is one issue that I originally filed against gdb:
> https://sourceware.org/bugzilla/show_bug.cgi?id=26525
> But that is most likely a bug in gcc. Jakub has a patch that fixes the
> issue for gcc, but there is some debate whether that is the correct
> approach or not:
> https://gcc.gnu.org/pipermail/gcc-patches/2020-August/552535.html
> 
> Note that I haven't really looked for issues in languages other than C
> or C++, so someone might want to double check whether other languages
> supported by gcc are also ready to switch to DWARF5 by default.
> 
> During the BoF Pedro mentioned that the GDB DWARF5 .debug_names support
> is incomplete/wrong. I was wondering whether there was a good
> description of the issue and/or a bug report for it. When using the
> contrib/gdb-add-index.sh it does add a .gdb_index for objects
> containing DWARF5 and the results seem correct, gdb also seems to be
> able to use it. When adding -dwarf-5 it seems to output a .debug_names
> section which can be read by binutils readelf (elfutils doesn't yet
> support .debug_names). I couldn't immediately see in what way it was
> wrong/incomplete.
> 

I filed a few issues related to .debug_names:
- https://sourceware.org/bugzilla/show_bug.cgi?id=25969
- https://sourceware.org/bugzilla/show_bug.cgi?id=25950
- https://sourceware.org/bugzilla/show_bug.cgi?id=25953

Thanks,
- Tom

> dwz does support .gdb_index rewriting, but doesn't know about
> .debug_names yet. So could we as a first step, when switching the
> DWARF5 keep using .gdb_index? At least till any issues with gdb
> .debug_names are resolved and dwz supports it?
> 
> Thanks,
> 
> Mark
>