Re: [RFA 4/4 take 2] Improved linker-debugger interface

[Jan Kratochvil <jan.kratochvil@redhat.com>]

Hi Gary,

On Fri, 21 Sep 2012 14:35:56 +0200, Gary Benson wrote:
> I've also passed --with-expat to force the issue.  I'm not seeing the
> XML warning any more, but the tests are still using the probes code
> and not the code from linux-low.c.

The tests are using linux-low.c:

../gdb gdb.base/break-probes -ex 'target remote localhost:1234' -ex 'set stop-on-solib-events 1' -ex 'set debug remote 1' -ex c
[...]
Sending packet: $qXfer:libraries-svr4:read::0,fff#91...Packet received: l<library-list-svr4 version="1.0" main-lm="0x7ffff7ffe2a8"><library name="/lib64/ld-linux-x86-64.so.2" lm="0x7ffff7ffd998" l_addr="0x7ffff7ddc000" l_ld="0x7ffff7ffcdd8"/></library-list-svr4>
SVR4:PASS
Sending packet: $z0,7ffff7ddf702,1#00...Packet received: OK
[...]
Sending packet: $z0,7ffff7df0285,1#d2...Packet received: OK
Stopped due to shared library event (no libraries added or removed)
(gdb) _

It has stopped on probe due to stop_on_solib_events == 1 but that is unrelated
to how solib-svr4.c fetches the library list.

I see the implementation for the linux-low.c side may not be so easy as
I thought about before.

GDB still needs to stop at the stap probes as it does but:

 * gdbserver needs to fetch probe arguments on its own.  Therefore GDB client
   needs to compile the arguments into AX (agent-expression) and upload them
   to gdbserver.  gdbserver then can do the incremental fetching of solist
   entries like solib-svr4.c with your patches does.

   * svr4_handle_solib_event should disable updating the local list of shared
     libraries as svr4_current_sos->svr4_current_sos_via_xfer_libraries will
     accomplish everything without needing svr4_handle_solib_event.

 * It could transfer only differences of <library-list-svr4> although that is
   an add-on optional feature.  The major reason for implementing
   <library-list-svr4> was the high amount of pings over long latency links.
   The amound of transferred data over wire may not be such a concern.
   Although with your high-performance solib goals it may be also your goal.

I had to clear it up for myself so I wrote it down, I hope I have it right.


Thanks,
Jan