Re: F34 Change proposal: Debug Info LLDB Index (System-Wide change)

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On Wed, 30 Sep 2020 02:11:34 +0200, Neal Gompa wrote:
> Why don't you add an lldb-add-index tool to generate LLVM indexes for
> LLDB?

Because doing it separately like GDB does is a wrong thing for
edit-compile-debug cycle. When clang (lld for LTO) has all the data incl. IR
already in memory it can much more faster produce the index for it.

With gdb-add-index it is questionable whether to use it or not for
edit-compile-debug cycles. If you run debugger just once for the compiled
program it is slower to generate + use the index just once than to run the
debugger without any index.

The index production performance does not matter much for rpmbuild as that
takes a long time anyway. But keeping the end-user edit-compile-debug cycle
unified with rpm build process makes the code path more tested and more
simple.


> Then we just invoke it as part of the buildroot policy setup and
> get both GDB and LLDB indexes? This proposal seems to be particularly
> destructive to GDB users to favor LLDB.

I do not see how this affects GDB. This Change expects clang will produce
.debug_names and rpmbuild will call gdb-add-index which will add .gdb_index.
Then there will be both indexes for both debuggers.

That is not great longterm but in some time GDB should fix its .debug_names
consumer to be compatible with the DWARF-5 standard and then Fedora can drop
.gdb_index completely.

(TBH I am not completely sure that LLDB conforms to the DWARF-5 standard as
the standard is not too descriptive of the format. But LLDB is at least more
.debug_names standard compliant despite "more compliant" may sound funny.)


> I personally don't use LLDB for *anything*, since I think it's not a
> particularly good debugger right now,

Please do not be offensive to the other toolchain. I also must not be so it is
unfair. I could argue with numbers but I won't.


> performance of debugging clang-built things with GDB degraded.

This is not intended/expected.


Jan
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