From: Florian Weimer <fweimer@redhat.com>
To: Rich Felker <dalias@libc.org>
Cc: Yehuda Yitchak <yehuda80@gmail.com>, musl@lists.openwall.com
Subject: Re: [musl] Accessing Thread-Local-Storage in GDB
Date: Wed, 09 Feb 2022 21:44:13 +0100 [thread overview]
Message-ID: <87h797zs6a.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <20220209183326.GB7074@brightrain.aerifal.cx> (Rich Felker's message of "Wed, 9 Feb 2022 13:33:26 -0500")
* Rich Felker:
> On Wed, Feb 09, 2022 at 09:32:10AM +0200, Yehuda Yitchak wrote:
>> Hello
>>
>> one of the applications i am debugging is compiled using MUSL libc
>> (aarch64) Version 1.1.19
>> when i inspect a core-dump and try to view TLS variables with "print
>> __percpu_dev" gdb (v8.3) complains:
>>
>> Cannot find thread-local storage for LWP 22873, executable file
>> <core-dump-file>
>> Cannot find thread-local variables on this target
>>
>> Any idea how I can overcome this?
>> Appreciate if you could CC me since i'm not subscribed.
>
> I think this is a consequence of gdb wanting to have a libthread_db (a
> GNU- and Solaris-ism) to tell it how to interact with the threads
> implementation of the process being debugged rather than just doing
> things in a libpthread-agnostic way like musl wants it to do. I think
> it should be fixable on the gdb side without too much headache, but I
> don't know how.
GDB would have to poke at libc internals and basically reimplement
__tls_get_addr. Maybe something can be done by calling libc ABI
functions for TLS access instead, but that doesn't work for core files.
> As a workaround, if the program is dynamic-linked, you can do
> something like print *(int *)dlsym(0, "foo") from the relevant thread
> context and it should work.
This only works if foo is a dynamic symbol (and if you aren't examining
a coredump).
My interest in initial-exec TLS (despite its impact on dlopen) is
somewhat motivated by a desire to make things easier for debuggers.
Thanks,
Florian
next prev parent reply other threads:[~2022-02-09 20:44 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-09 7:32 Yehuda Yitchak
2022-02-09 18:33 ` Rich Felker
2022-02-09 20:44 ` Florian Weimer [this message]
2022-02-09 22:31 ` Rich Felker
2022-02-10 11:23 ` Florian Weimer
2022-02-10 18:05 ` Yehuda Yitchak
2022-02-10 21:32 ` Rich Felker
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