Re: Some questions w.r.t remote watchpoint support in i386

[Wu Zhou <woodzltc@cn.ibm.com>]

> > 1. The first error I encounter is: "Couldn't write debug register: No such
> > process". 
> > 
> > After some tracking, I found gdb client is calling target_insert_watchpoint
> > defined in config/i386/nm-i386.h, instead of the remote_insert_watchpoint 
> > defined in remote.c
> > 
> > I guess this is a more general problem.  Whenever you change target under 
> > i386 platform, you will always get the i386_insert_watchpoint (and other 
> > three target operations) executed.
> > 
> > Maybe we can put these target operation into the target_ops, instead of 
> > defining them as macro in config/i386/nm-i386.h?  
> 
> Yes, someone needs to fix this.

I had a closer look at this.  It seems this will involve quite a few gdb 
configs.  Almost all the native header files in config/i386 include 
nm-i386.h, but their responsive native c source are very different.  To 
delete these macros in nm-i386.h, I believe we need to put their 
counterpart target vectore into all these responsive native c source.
And we also need to test that all relevant configs are ok after the 
changes.  It seems hard to me.  Anyone have any good idea?

> 
> > 2. Following the above thought, I comment out these four macros in 
> > config/i386/nm-i386.h, and add them into i386-linux-nat.c
> > 
> > This time, local gdb will call remote_insert_watchpoint indeed, but I get 
> > another error:
> > 
> >  Can't clear hardware watchpoints without the 'Z2' (write-watchpoint) packet.
> > 
> > "set debug remote 1" tell me that Packet Z2 (write-watchpoint) is NOT 
> > supported
> > 
> > I tried to use "set remote  write-watchpoint-packet 1", but it won't work 
> > either:
> > 
> >  Enabled packet Z2 (write-watchpoint) not recognized by stub
> > 
> > my question here is:
> > 
> > What is the stub refered to here?  Is it the gdbserver?  And how can 
> > gdbserver determine which packat he will support, which won't?  
> 
> The stub is gdbserver, yes.  It supports what it supports, and does not
> support what no one has implemented!  And no one has implemented i386
> watchpoints for gdbserver.

It seems that there is not many requirement for this?  Maybe i386 is not a 
very popular gdbserver platform.  :-)


Regards
- Wu Zhou