Re: [PATCH 4/5] libdwfl: cache Dwfl_Module and Dwarf_Frame for Dwfl_Frame

[Mark Wielaard <mark at klomp dot org>]

On Wed, 2019-10-30 at 16:55 -0700, Omar Sandoval wrote:
> On Wed, Oct 30, 2019 at 02:04:42PM +0100, Mark Wielaard wrote:
> > Hi Omar,
> > 
> > On Mon, 2019-10-07 at 02:05 -0700, Omar Sandoval wrote:
> > > The next change will need to have the Dwarf_Frame readily available, so
> > > rather than finding it again every time, let's cache it for reuse. The
> > > CFI frame can also be useful to clients of libdwfl, so add
> > > dwfl_frame_dwarf_frame to get it. Similarly, the Dwfl_Module is also
> > > frequently needed in conjunction with the frame, so cache it and add
> > > dwfl_frame_module.
> > 
> > I can see how this is useful. But it seems the Dwarf_Frame is only
> > cached when __libdwfl_frame_unwind is called. Which I believe isn't
> > done for the initial frame. Also it isn't clear how to propagate any
> > errors when NULL is returned. Maybe dwfl_frame_dwarf_frame () should
> > check first to see if frame is NULL and then call lookup the CFI and
> > call dwarf_cfi_addrframe if not?
> 
> Yes, that makes sense. Rather than doing the lookups in
> __libdwfl_frame_unwind and handle_cfi, I can move the lookups to
> dwfl_frame_module and dwfl_frame_dwarf_frame, have those functions cache
> it internally, and make __libdwfl_frame_unwind and handle_cfi call those
> functions.

dwfl_frame_dwarf_frame should also save any errors, so that when it is
called again it can set it again when returning NULL. Like what
dwfl_module_getdwarf does.

Thanks,

Mark