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

[Michael Snyder <msnyder at redhat dot com>]

Eli Zaretskii wrote:
> 
> On Tue, 27 Mar 2001, Mark Kettenis wrote:
> 
> >    Sorry, I'm not following.  The watchpoint-related macros are defined
> >    on files which should be used only with native debugging (i386-nat.c
> >    and nm-i386.h).  On top of that, the macros only get exposed if the
> >    port defines I386_USE_GENERIC_WATCHPOINTS.  A port which doesn't want
> >    that should get rid of the watchpoints for free, by simply not
> >    defining I386_USE_GENERIC_WATCHPOINTS.
> >
> >    Which part of the above misfires, and why?
> >
> > It used to be possible to debug a remote i386 target with a native
> > Linux/x86 debugger.
> 
> This sounds as The Source of All Evil, doesn't it? 

No, it's quite common.  A sparc-solaris gdb can debug
embedded sparc boards, for instance.

> Can GDB really be
> tweaked into debugging a remote target with a native debug code?  I'm
> surprised that it even works, unless there are some extra-special hacks
> lying around, just for this.

It works.  Or it used to...  and it's quite important that it
continue to work, for debugging embedded Linux.

> 
> >    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.