Re: [cagney_convert-20030606-branch] Add value to REGISTER_TO_VALUE et.al.

[Andrew Cagney <ac131313@redhat.com>]

>    Anyway, the question of what to do when the register's value can't be 
>    found has been largely ignored.  I'm thinking that throwing an error 
>    would be a safer strategy - there is too much code ignoring register 
>    fetches and I don't think we're going to be auditing it soon.
> 
> Indeed, GDB depends on the frame unwinder always returning a value for
> its registers.  However for the sake of printing variables stored in
> registers it seems that setting OPTIMIZED_OUT makes sense if we know
> for certain that a the register has been thrashed.  It makes
> valprint.c:value_print() print "<value optimized out>".  The problem
> with printing an error message from REGISTER_TO_VALUE() is keeping the
> error messages uniform.  However, in some cases it might be more
> appropriate to print a warning instead of an error, for example if the
> register hasn't been saved, but if we cannot tell whether it has been
> thrashed yet.
> 
> However, I can live with the current status quo.

Well, the status quo is that GDB doesn't have a story :-(  GDB throws an 
error for some values (memory read failures), returns bogus values for 
others (register not available), and sets optimized out for more.

As a pie in the sky, would printing better messages help, vis:

	<optimized out>
or
	<register r10 unavailable>
or
	<memory error at 0x1234>
or
	<register r11 invalid>

What of the user interface, should it expect to be able to catch such 
errors?

Andrew