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RFC: A mode in which gdb avoids libthread_db
- From: Daniel Jacobowitz <drow at mvista dot com>
- To: gdb at sources dot redhat dot com
- Date: Sat, 26 Jul 2003 11:58:20 -0400
- Subject: RFC: A mode in which gdb avoids libthread_db
Recent Linux kernels (2.5.30 and later; theoretically the latest Red Hat
2.4.20 kernels also include it, but I observed some badness in testing...)
support some ptrace extensions I designed which make it possible to debug
multi-threaded applications without using libthread_db at all. The only
things we'll lose are:
- Potential high-level information, like mutex status - right now we
don't have this at all on GNU/Linux.
- TLS access - this could be easily fixed by handling each platform's
TLS ABI directly from GDB, and there's a comment to that effect in
GDB's source already.
- TIDs - we'd only have the application's LWP IDs, not the thread IDs
that LinuxThreads/NPTL use.
Things we'll gain:
- A lot of libthread_db-related bugs would go away. For instance,
the kfail in print-threads.exp, which hits a breakpoint after
LinuxThreads decides the thread has already exited.
- ABI simplicity - this would solve the x86-64/i386 issue, and similar
problems on MIPS.
- Support for debugging clone-based 1-1 threading which doesn't use
libpthread.so.
Once the pending fork-debugging patch is accepted, most of the machinery
we'd need to do it will be in place, too. Thoughts? Worthwhile?
--
Daniel Jacobowitz
MontaVista Software Debian GNU/Linux Developer