Re: [00/19] Eliminate some more current_gdbarch uses

[Pedro Alves <pedro@codesourcery.com>]

On Friday 05 June 2009 23:52:25, Tom Tromey wrote:
> >>>>> "Pedro" == Pedro Alves <pedro@codesourcery.com> writes:
> 
> Pedro> - We should do something smarter about longjmp breakpoint
> Pedro>   lookup at some point.
> 
> If you have something in mind, I would like to hear it.
> The next-over-throw patch does something very similar to the longjmp
> code; I would be happy to update both at once.

I *know* we can do smarter, but exactly what's the best, I haven't
thought much about.  Some data points / suggestions:

 - longjmp breakpoints need to be installed as long as there's a
   thread nexting or stepping or whatever command that needs those,
   for non-stop mode.  The fact that they're momentary breakpoints
   makes it so that a thread that is "continue"ing, simply thread
   hops them, since momentary breakpoints are thread specific, which is
   more efficient than having them all
   set longjmp-resume, hit-longjmp-resume,resume.  The breakpoint location
   machinery takes care of not installing duplicates.  The set of addresses
   where to install such breakpoints however, don't change per-address
   space --- we could cache minimal symbols on a per symbol/address space
   generic framework (similar to objfile_data), and reparse that only when
   symbols change (that is, breakpoint_re_set or similar).

 - perhaps the simplest and most likely the most effective easily: we
   can use the objfile_data mechanism to cache if there are longjmp-like
   functions in a given objfile.  No use looking up the minimal symbol
   everytime.

 - lookup_minimal_symbol still does a linear walk on all objfiles
   when you pass it an objfile.  That may matter a bit.  We could
   split that function in two to not do that loop when we know the
   objfile in advance.

 - we can move the update_global_location_list to the caller of
   create_longjmp_breakpoint, cutting its frequency by 4, if that
   matters.  Probably not currently.

-- 
Pedro Alves