Re: Non-stop multi-threaded debugging

["Ulrich Weigand" <uweigand@de.ibm.com>]

Nathan Sidwell wrote:

> A client of CodeSourcery's has contracted with us to implement a
> number of new features in GDB, some of which have been on the
> frequently requested list for quite some time:

Thanks, these are indeed very interesting and useful features.

> - We're to implement a limited form of multi-process debugging.
> 
>    Full multi-process debugging would entail changes to
>    1) process management code,
>    2) target interfaces, and
>    3) symbol tables.

> Our client would very much like for this work to be incorporated into
> the public GDB sources (although they understand that the decision is
> in the public project's hands), so we'll be posting our design
> thoughts for general discussion.  In particular, I believe the
> multi-process work may overlap with some of the work IBM has done to
> support the Cell processor; we'd very much like to work with IBM to
> ensure that the final model is appropriate for both our client and for
> Cell developers.

It looks like the points 1) and 2) you are planning to address 
actually do *not* overlap with the work we've been doing on the
Cell combined debugger.  The Cell programming model our debugger
supports is bascially a regular multi-threaded model, except that
some threads may execute either PowerPC or SPU architecture code
at any time.  Multi-process support is not required.

[ However, of course multi-process support would be a nice *extension*
to the Cell combined debugger, allowing to debug multiple processes,
each of which follows the normal multi-threaded Cell model. ]

Point 3) above would be relevant to the Cell combined debugger as well.
You do not address this point in more detail in your document, but I
assume this would imply introducing the notion of "address spaces" and
associating symbol tables to a particular address space.  Something
similar is already needed for the Cell combined debugger, as we have
multiple address spaces even within a single process.  I'm definitely
interested in working on adding this support to mainline GDB -- if
that then also helps the multi-process work, that's an additional
benefit.


Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com