Re: Getting the i386 watchpoints into the taget vector?

[Andrew Cagney <ac131313 at ges dot redhat dot com>]

> > Date: Thu, 19 Sep 2002 21:57:40 -0400
> > From: Andrew Cagney <ac131313@ges.redhat.com>
> >
> > Instead of using a system interface, the i386 manipulates the
> > hardware watchpoint registers directly.
>
> Really?  What I see is that most i386 ports use ptrace or similar
> interfaces to access the hardware watchpoints.  So in what sense is
> this manipulation ``direct''?
(Probably bad choice of words).

GDB can implement watchpoints, for a remote target, using two mechanism:

- sending the remote target the watchpoint request (the Z packet) and 
let the remote target implement the details

- manipulate the h/w watchpoint registers directly, sending the remote 
target register read/write operations - what I believe i386-nat.c does.

The native equivalents are roughly:

- use some sort of custom h/w watchpoint kernel interface

- use ptrace(PT_GETREGS) / ptrace (PT_SETREGS)


> > One thought is to change the config/i386/nm-i386.h macros to something 
> > native specific (native_insert_watchpoint()) and then have the various 
> > native targets (infptrace.c, ...) add these methods to their target vector.
> >
> > It does restrict things to native targets.  A remote target couldn't 
> > make use of GDB's built-in knowledge of watchpoint registers.
> >
> > Another (less well thought out) idea, is for the target stack, to fall 
> > back to the ``native watchpoint'' mechanism when the [remote] target 
> > doesn't support watchpoints. I think this would mean putting the 
> > ``native watchpoint'' methods in the architecture vector where the 
> > target vector code could call it.
>
> Why not simply allow remote targets define the watchpoint-related
> macros?  Let their definitions issue remote packets that will cause
> the target end DTRT.  As long as the target is a i386-compatible
> machine, the internal bookkeeping we have in the current code will
> work.
I'm not sure what you mean here.  If we used macro's then they would run 
afowl of trying to make everything multi-arch.

Andrew

PS: Someone should implement the equivalent sim commands.  sim/common 
has a watchpoint framework.  Just needs the sim<->gdb interface.