[llvm-dev] llvm-dev Digest, Vol 153, Issue 85

[David Blaikie via llvm-dev]

On Fri, Mar 17, 2017 at 3:19 AM George Rimar <grimar at accesssoftek.com>
wrote:

> >FWIW - selfhosting I did find that GDB wasn't able to find the source code
> >for some functions when using LLD's gdb_index, so I've switched back to
> >gold+gdb_index for now (given the performance problems you mentioned,
> >sounds like I wasn't gaining much/anything in terms of link time by using
> >lld anyway).
> >
> >On Thu, Mar 16, 2017 at 11:17 AM Rui Ueyama <ruiu at google.com> wrote:
> >
> >> I personally haven't tried gdb_index, and I don't know the quality of
> the
> >> produced index. Most of the code was written by George.
> >>
> >> One thing I noticed about the feature (and filed as
> >> http://bugs.llvm.org/show_bug.cgi?id=32228) is that our gdb_index
> feature
> >> is much slower than the gold. Apparently there's room for improvement.
>
> I also do not have information about quality of index. At simple tests
> output was
> equal to what gold produced for me.
>
> I plan to start woring on PR32228 at next week, hope will be able to solve
> perfomance
> problems and may be it will reveal more details about index quality.
>

Sounds good - I took only a cursory glance at the llvm-dwarfdump of the
index, and it looked like (though I may be mistaken) the dump output
included implementation details (like hashes, buckets, etc) so it wasn't
easy to compare the dump from a GCC-built binary with a Clang-built binary
to compare them/see what was missing, etc.

Maybe it'd be worth having a mode that dumped the contents canonicalized
(sorted, etc) in some way that'd be easy to compare?

(then again, perhaps it's the structure that's the problem - maybe all the
data's there, but there's a bug in the hashing that makes it invalid/unable
for GDB to use it correctly)

Happy to try to help you with it.

- Dave


>
> George.
>
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