Re: [PATCH]: Make Linux use the new unified x86 watchpoint support

[Eli Zaretskii <eliz@delorie.com>]

> Date: Tue, 27 Mar 2001 08:54:14 -0800
> From: Michael Snyder <msnyder@redhat.com>
> 
> > >    This possibility has been discussed back in November, but the
> > >    conclusion was that it's not a good idea.  I don't remember the
> > >    details, but the reasons had something to do with threads and how
> > >    the register cache is used in conjunction with threads.  (I can dig
> > >    out the URLs of the relevant messages, if you want to read them.)
> > >
> > > I suggested doing this, but several people objected to exposing the
> > > debug registers in this way.  Threads have nothing to do with it
> > 
> > I'm quite sure they did.  IIRC, the issue was that debug registers are
> > global, whereas normal registers are per thread.
> 
> Mmmmm... that's probably true.  However the effect would just be
> that all threads appear to have the same values for debug regs.
> If you change them in one, they'll change in all.

As far as I understood, GDB's regcache cannot do such magic.  It
assumes that all the registers are per thread, so if you change them
in one thread, the other threads' registers remain unchanged in the
cache.

In other words, this kind of global registers is (or was when we
discussed it) incompatible with how regcache works.  That is why I was
advised not to introduce the debug registers into the regcache.