Re: Getting the i386 watchpoints into the taget vector?

[Andrew Cagney <ac131313@ges.redhat.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.