Re: bitwise operations on registers

[Daniel Jacobowitz <drow@mvista.com>]

On Mon, Mar 11, 2002 at 10:35:11AM -0500, Andrew Cagney wrote:
> >On Sun, 10 Mar 2002, Andrew Morton wrote:
> >
> >
> >>(gdb) p $esp & 4
> >>Argument to arithmetic operation not a number or boolean.
> >>(gdb) 
> >>
> >>I don't seem to be able to perform the `&' and `|' arithmetic
> >>operators against machine registers.
> >
> >
> >"p $eax & 4" works for me.  Doesn't it work for you?
> >
> >As for $esp, I think GDB knows that it's not a number, so try
> >
> >  (gdb) p (int)$esp & 4
> >
> >(I don't know whether the built-in knowledge GDB has about $esp should 
> >prevent it from working without the cast, though.)
> 
> Yes, try:
> 	(gdb) p (void*)0 & 4
> So, this a bug?

I think so.  C won't let you do it either, but historically we've been
more permissive than C about things that have a clearly defined
meaning, and this does.

-- 
Daniel Jacobowitz                           Carnegie Mellon University
MontaVista Software                         Debian GNU/Linux Developer