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

[Michael Snyder <msnyder at redhat dot com>]

Eli Zaretskii wrote:
> 
> On Mon, 26 Mar 2001, Michael Snyder wrote:
> 
> > Guys, this implementation has problems.  You have it hard-coded so that on a
> > linux host, it unconditionally calls native linux methods involving ptrace
> > to get the debug registers.  This breaks very badly if you're using a native
> > linux host to debug a remote i386 target.
> 
> 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?

The gdb was configured for native linux, but until this change, 
it was also able to be used to debug a remote embedded i386
target.  This change breaks that, because it makes ptrace calls.
If debugging target remote, there is no process on the host machine
on which to make a ptrace call.

> 
> > Seems to me, what you need to do is add these debug registers to the
> > reg cache, and treat them like ordinary registers.
> 
> 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.)
> 
> > Then you can just use the ordinary read_register interface to get
> > them, and remote.c will do the right thing for you (assuming the
> > target knows about these extra registers).
> 
> Mark explicitly didn't want the watchpoint code to be in the
> target-depenent files, so watchpoints cannot currently work for remote
> targets.

I don't mind if watchpoints don't work for remote targets --
but the code as written prevents me from debugging a remote
target at all.