The following patch fixes a problem with breakpoints set in shlibs that are 
manually loaded/unloaded by the program.  What currently happens is that pending 
breakpoints work properly for the first run of the program.  On the 2nd run, the 
resolved breakpoint(s) can end up at the start of the breakpoint list and is 
marked bp_shlib_disabled.  This is fine for a bit and we reach the breakpoint 
again when the shared library is loaded.  However, when we unload the 2nd time, 
there is trouble.  We eventually get a shlib_event from the dlclose() and we 
attempt to remove the breakpoint to step over it.  Unfortunately, we try and 
remove all breakpoints and we end attempting to remove a breakpoint that no 
longer exists (remember the breakpoint for the shared library routine is now at 
the start of the breakpoint list).  We fail trying to remove the first 
breakpoint and end up failing remove_breakpoints.  We subsequently keep running 
into the shlib_event breakpoint over and over again ad-infinitum.

To fix this, I have added an observer for a new event: solib_unloaded.  When 
update_solib_list discovers a shared library has been unloaded, it notifies all 
observers (initially this is just breakpoint.c).  Breakpoint.c sets up an 
observer to find all breakpoints in the removed shlib and mark them as 
non-inserted and bp_shlib_disabled.  This solves the problem.

I also added code to re_enable_breakpoints_in_shlibs to remove the error 
messages we get when we go and rerun the program (it attempts to find shlib 
breakpoints in every shared library that gets loaded).

I have included a new test case which exercises the scenario.

Ok to commit?

-- Jeff J.

2004-08-10  Jeff Johnston  <jjohnstn@redhat.com>

         * observer.sh: Add struct so_list declaration.
         * Makefile.in: Add dependencies on observer.h for solib.c and
         breakpoint.c.
         * breakpoint.c (disable_breakpoints_in_unloaded_shlib): New
         function.
         (_initialize_breakpoint): Register
         disable_breakpoints_in_unloaded_shlib as an observer of the
         "solib unloaded" observation event.
         (re_enable_breakpoints_in_shlibs): For bp_shlib_disabled breakpoints,
         call decode_line_1 so unfound breakpoint errors are silent.
         * solib.c (update_solib_list): When a solib is discovered to have
         been unloaded by the program, notify all observers of the
         "solib unloaded" observation event.

2004-08-10  Jeff Johnston  <jjohnstn@redhat.com>

         * gdb.base/unload.exp: New test for breakpoints in dynamically
         loaded libraries.
         * gdb.base/unload.c: Ditto.
         * gdb.base/unloadshr.c: Ditto.