From: Florian Weimer <fweimer@redhat.com>
To: Pedro Alves <pedro@palves.net>
Cc: Simon Marchi <simon.marchi@polymtl.ca>,
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 18:43:47 +0200 [thread overview]
Message-ID: <87blaenprw.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <a165a92e-23b5-5b1b-31e1-6a878737932d@palves.net> (Pedro Alves's message of "Fri, 16 Apr 2021 17:33:14 +0100")
* Pedro Alves:
> On 16/04/21 17:28, Florian Weimer wrote:
>> * Pedro Alves:
>>
>>> IIRC, the order which libraries are loaded by GDB hasn't changed. The
>>> issue is that until recently (before glibc 1daccf403b1b), the stacks
>>> lists lived in libpthread (stack_used/__stack_user), so the fact that
>>> GDB loaded libthread_db.so before ld.so's symbols were loaded didn't
>>> make a difference. Now they were moved to ld.so, so libthread_db.so
>>> can't find them until GDB reads the ld.so symbols. Is this assessment
>>> correct?
>>
>> Yes, I believe this is what happens.
>>
>
> OK, I believe what is confusing in your commit log was the reference to
> two different kinds of "loaded":
>
> "libthread_db is loaded once GDB encounters libpthread, and at this
> point, ld.so may not have been loaded yet. "
>
> The first loaded is about GDB dlopening libthread_db.so. The second loaded
> refers to reading symbols -- ld.so has been loaded by the inferior already
> at that point.
>
> It would be clearer as:
>
> "libthread_db is loaded once GDB encounters libpthread, and at this
> point, ld.so's symbols may not have been read by GDB yet. "
I'm going to go with:
“
libthread_db is loaded once GDB encounters libpthread, and at this
point, ld.so may not have been processed by GDB yet.
”
> If I understood that correctly, then the following sentence is also a
> bit confusing:
>
> "As a result, _rtld_global cannot be accessed by regular means from
> libthread_db."
>
> Because that sounds to me like you were perhaps talking about some
> magic means to reference globals, some magic relocations, or some
> other magic voodoo only understood by glibc experts.
We use the magic that GDB provides to us (ps_pglobal_lookup, I think).
I thought that this was understood by GDB experts only. 8-)
Thanks,
Florian
next prev parent reply other threads:[~2021-04-16 16:43 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 [this message]
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
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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