From: Simon Marchi <simon.marchi@polymtl.ca>
To: Pedro Alves <pedro@palves.net>, Florian Weimer <fweimer@redhat.com>
Cc: libc-alpha@sourceware.org, gdb-patches@sourceware.org,
Emil Velikov <emil.l.velikov@gmail.com>,
Kevin Buettner <kevinb@redhat.com>
Subject: Re: [PATCH glibc] nptl_db: different libpthread/ld.so load orders (bug 27744)
Date: Fri, 16 Apr 2021 13:33:26 -0400 [thread overview]
Message-ID: <78edaf4c-e2f2-8d4e-0950-98ba24367921@polymtl.ca> (raw)
In-Reply-To: <daf02031-c30e-7bf9-c5a8-047c497406b1@palves.net>
On 2021-04-16 1:18 p.m., Pedro Alves wrote:
> On 16/04/21 17:53, Simon Marchi wrote:
>
>> Do we need / want to fix GDB if this goes in glibc then?
>
> I think so. We may need to discuss more the "needs_setup" hack, but we
> can do that in that thread.
In the new version I add a new inferior flag "in_initial_library_scan".
It's perhaps not ideal but the result is better than what I had in v1.
But yeah let's discuss that in that thread.
> Given that libpthread.so is going away in the future, we should be thinking about
> addressing that as well. Does your patch fix that as side effect?
No, I think of that as a separate problem.
>
> If not, GDB should be keying the loading of libthread_db.so on something else.
> Making GDB try to load libthread_db in reaction to processing ld.so instead
> libthread_db.so would fix that, I think. And, it would fix this ordering problem at
> hand as well. So if we do that, maybe we don't need the other changes.
Is it possible to have a completely static executable that doesn't use
ld.so but uses pthreads?
I don't think that would work well for the "run" case, where ld-linux
arrives before libpthreads.so (and before libc.so, for when pthreads is
moved to libc.so). If we try to load libthread_db when ld-linux
appears, the symbols provided by libpthreads (or libc) won't be found.
We would have to key the loading on when both libpthread and ld-linux
are there (or both libc and ld-linux).
Another problem with the current state (but that would be fixed with
Florian's patch I think) is that gdb has this setting "set
auto-solib-add". If off, GDB won't load the symbols of shared
libraries. _Except_ if the library if libpthread:
https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=gdb/solib.c;h=d32b2210005fdd6a5013cfd566620d6afeae9cf6;hb=HEAD#l968
But it means that if auto-solib-add is off, we won't load ld.so's
symbols, and we fall back on the original problem, even if the ordering
is right. Since Florian's patch makes libthread_db only access symbols
of libpthread.so, I think that avoids this issue as well.
But then when libpthreads is moved into libc, we'll have the problem
that libthread_db simply won't get loaded...
Simon
next prev parent reply other threads:[~2021-04-16 17:33 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-16 15:56 Florian Weimer
2021-04-16 16:07 ` Simon Marchi
2021-04-16 16:12 ` Florian Weimer
2021-04-16 16:25 ` Pedro Alves
2021-04-16 16:28 ` Florian Weimer
2021-04-16 16:33 ` Pedro Alves
2021-04-16 16:43 ` Florian Weimer
2021-04-16 16:47 ` Pedro Alves
2021-04-16 16:53 ` Simon Marchi
2021-04-16 17:18 ` Pedro Alves
2021-04-16 17:26 ` Florian Weimer
2021-04-16 17:33 ` Simon Marchi [this message]
2021-04-16 18:29 ` Pedro Alves
2021-04-16 18:35 ` Florian Weimer
2021-04-16 17:28 ` Florian Weimer
2021-04-16 17:43 ` Pedro Alves
2021-04-19 9:06 ` Florian Weimer
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