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Date: Tue, 25 Aug 2015 18:22:00 -0000
From: Jan Kratochvil <jan.kratochvil@redhat.com>
To: Paul Pluzhnikov <ppluzhnikov@google.com>
Cc: gdb-patches ml <gdb-patches@sourceware.org>,        Pedro Alves <palves@redhat.com>
Subject: Re: [patch][rfc] Allow GDB to search for the right libthread_db.so.1
Message-ID: <20150825182212.GB9494@host1.jankratochvil.net>
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On Tue, 25 Aug 2015 20:13:54 +0200, Paul Pluzhnikov wrote:
> We've had a lot of systems where installed /lib64/libthread_db was
> from glibc-2.7, while target binary was using glibc-2.3.6, and I am
> 99.99% sure that combination didn't work.

Pedro explained that glibc also does:

# $ grep -rn nptl_version nptl*
# nptl/ChangeLog.old:7461:        * init.c (nptl_version): Add __attribute_used__ to nptl_version.
# nptl/nptl-init.c:68:static const char nptl_version[] __attribute_used__ = VERSION;
# nptl_db/td_ta_new.c:42:  if (td_lookup (ps, SYM_nptl_version, &versaddr) != PS_OK)
# nptl_db/structs.def:53:DB_SYMBOL (nptl_version)
#
# So that alone makes a libthread_db.so for glibc 2.x refuse to work with glibc 2.y.

BTW the nptl_version check seems to predate the _thread_db_* symbols.


Thanks,
Jan