From: Ilya Leoshkevich <iii@linux.ibm.com>
To: Tom Tromey <tromey@adacore.com>
Cc: Ulrich Weigand <ulrich.weigand@de.ibm.com>,
Andreas Arnez <arnez@linux.ibm.com>,
binutils@sourceware.org
Subject: Re: [PATCH] gdb: do not add const sections to the section map
Date: Thu, 19 May 2022 19:37:03 +0200 [thread overview]
Message-ID: <f3670a73b6d55e98ac713898083333489df4af4f.camel@linux.ibm.com> (raw)
In-Reply-To: <875ym1d0dw.fsf@tromey.com>
On Thu, 2022-05-19 at 09:10 -0600, Tom Tromey wrote:
> > > > > > Ilya Leoshkevich <iii@linux.ibm.com> writes:
>
> > From: Ulrich Weigand <ulrich.weigand@de.ibm.com>
> > build_objfile_section_table () creates four synthetic sections,
> > which
> > significantly slow down section map sorting. This is especially
> > noticeable when debugging JITs that report a lot of objfiles.
> > Since
> > these sections are not useful for find_pc_section (), do not add
> > them
> > to the section map.
>
> How does it slow down the sorting?
CoreCLR JIT reports each compiled function as a separate objfile with
a single .text section and a few debug sections [1]. Once you have a
few thousand of them - which is easily reachable - std::sort becomes a
bottleneck. Ignoring synthetic sections from each objfile reduces the
amount of sections to sort significantly.
That's unfortunately not quite enough to debug bigger apps. But it's
still a noticeable improvement, so I've decided to post it.
I'm currently trying to implement a more complex optimization in the
section map area ([2] - not working yet, and probably not reviewable
either, just FYI).
> It seems a little strange at least to drop the *ABS* section, since
> IIUC
> that's for symbols that specify some kind of absolute address.
> Couldn't
> these matter for lookup purposes? It's probable I don't really know
> what's going on here...
All four seem to have a size of 0, so they should never be returned
by find_pc_section ().
> I wonder if we can drop all support for all these sections from gdb.
They were added in 65cf35635977, which introduced
gdb_bfd_section_index (). This function is used in quite a few places,
so I guess as long as bfd can report these sections, this should stay?
> Tom
[1]
https://github.com/dotnet/runtime/blob/v6.0.5/src/coreclr/vm/gdbjit.cpp#L2147
[2]
https://github.com/iii-i/binutils-gdb/releases/tag/section-map-20220519
prev parent reply other threads:[~2022-05-19 17:37 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-16 19:42 Ilya Leoshkevich
2022-05-17 14:52 ` Andrew Burgess
2022-05-19 15:10 ` Tom Tromey
2022-05-19 17:37 ` Ilya Leoshkevich [this message]
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