frame_register_read()

[Richard Earnshaw]

> > Andrew,
> > 
> > frame_register_read() contains the comment
> > 
> >   /* FIXME: cagney/2002-04-10: This test is just bogus.  It is no
> >      indication of the validity of the register.  The value could
> >      easily be found (on the stack) even though the corresponding
> >      register isn't available.  */
> >   if (register_cached (regnum) < 0)
> >     return 0;                   /* register value not available */
> > 
> > But in regcache.c we have
> > 
> > /* REGISTER_VALID is 0 if the register needs to be fetched,
> >                      1 if it has been fetched, and
> >                     -1 if the register value was not available.  
> >    "Not available" means don't try to fetch it again.  */
> > 
> > So why is the code in frame_register_read incorrect?  It's simply testing 
> > that the register exists for this target.  If it doesn't exist, then how 
> > can it be recovered from the stack?
> 
> Introspect (tracepoints, target snapshots) do this.  If a specific 
> snapshot doesn't contain a register then the register is unavailable. 
> The corresponding hardware still has the register so its value can be 
> found on the stack.

So it seems the comment in regcache.c is incomplete/misleading.  Could you 
clarify it?

R.