GDB support for thread-local storage

Andrew Cagney ac131313@cygnus.com
Thu Jun 20 18:35:00 GMT 2002


> I've posted a note to the Dwarf mailing list, describing the
> DW_OP_push_tls_address approach, and saying that we'll experiment with
> this as a GNU extension to Dwarf and write back when we've actually
> got something working.

Hmm, would you be able to post the prososal here?

> For STABS, we can simply invent a new symbol type, whose value is the
> offset within the thread-local storage block for the current thread
> for the module containing the stab.  I haven't written up a real
> proposal for STABS yet.
> 
> On Linux, Ulrich Drepper has added the following function to
> libthread_db:

Has solaris, or even MS, done anything in this area?  The 
LOC_THREAD_LOCAL_STATIC must have come from somewhere, dig dig, you may 
want to look at what HP/UX is getting up to.

> If you're not convinced it should be a target method, consider this:
> Remember that libthread_db isn't clean for cross-debugging.  It's a
> target library.  So at the moment, there are cases where gdbserver
> loads and uses libthread_db, not GDB itself.  In those cases, the
> tls_get_addr request needs to be sent across the network connection to
> gdbserver, td_thr_tls_get_addr needs to be invoked there, and the
> answer needs to be sent back.  By making tls_get_addr a target method,
> it's easy for the remote protocol layer to provide its own definition
> of the method and send a packet across for the request.

Similar to this, both SOFTWARE_SINGLESTEP and hardware breakpoints are 
ment to be implemented with support from both the target vector and the 
architecture vector.  By doing that, a sequence like:

	can target single step?
	  yes, step target
	else
	  use architecture to software singlestep target

can be implemented (in both cases it isn't so it can't, ulgh).

However, in the case of the above, is the architecture method needed? 
Given that th only thing implementing this will be the above GNU/Linux 
thread-db library, and GDB's linux thread code will know to call that 
directly.

BTW, what happens if the target doesn't have execution (i.e. a corefile).

Andrew

(Use thread_local_static rather than thr_tls in function names)




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