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To: Andrew Cagney <ac131313@cygnus.com>
cc: Richard.Earnshaw@arm.com, gdb@sources.redhat.com
Reply-To: Richard.Earnshaw@arm.com
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Subject: Re: frame_register_read() 
In-reply-to: Your message of "Tue, 14 May 2002 10:41:25 EDT."
             <3CE12215.1020308@cygnus.com> 
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Date: Tue, 14 May 2002 09:00:00 -0000
From: Richard Earnshaw <rearnsha@arm.com>
X-SW-Source: 2002-05/txt/msg00153.txt.bz2

> > 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.