Re: F34 Change proposal: Debug Info Standardization (from DWZ to -fdebug-types-section) (System-Wide Change proposal)

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* Jan Kratochvil:

> On Tue, 29 Sep 2020 22:29:44 +0200, Mark Wielaard wrote:
>> I was just discussing that recently with the Hotspot Perf GUI
>> maintainer. And we concluded that if .debug files would be compressed
>> then we would need an uncompressed cache somewhere. The issue with
>> having the on-disk debuginfo files compressed is that for
>> debugger/tracing/profiling tools it incurs an significant
>> decompression time delay and extra memory usage. Especially for a
>> profiling tool that only needs to quickly get a little information it
>> is much more convenient to be able to simply mmap the .debug file,
>> check the aranges and directly jump to the correct DIE offset. See
>> e.g. https://github.com/KDAB/hotspot/issues/115
>
> First is is a marginal use case.

Why do you think that?  Using debuginfo for perf and the like seems to
be much more common than actual debugging, based on what I see
downstream.

> The problem is that you have to wait for minutes for GDB to print anything.

Is this about slow tab completion?

> It is faster to add cout<<, recompile and rerun the program (with clang+lld as
> with g++ it takes more than 3x as much time) than to wait for GDB. LLDB would
> sure print it immediately but it is incompatible with Fedora DWARF. Enjoy.

I can't use LLDB because it does not support thread-local variables.
Not even initial-exec variables, which could be implemented without
peeking at glibc internals.

Thanks,
Florian
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