Hardware Breakpoints

Hardware Breakpoints

[Peter Jansen]

Hi,

I'm trying to use hardware breakpoints in gdb (in the new
gdbarchitecture stuff) and cannot figure out how it all works. Are their
any gdbarch things for hardware breakpoints and watchpoints?

Are there any targets that use hardware breakpoints and watchpoints in
the new gdbarch stuff?

Im working on a AVR target.

Thanks,

-- 
Peter Jansen
Smart Container
Level 1, NIC Building
Eveleigh
NSW       1430
AUSTRALIA

Re: Hardware Breakpoints

[Andrew Cagney]

> Hi,
> 
> I'm trying to use hardware breakpoints in gdb (in the new
> gdbarchitecture stuff) and cannot figure out how it all works. Are their
> any gdbarch things for hardware breakpoints and watchpoints?
> 
> Are there any targets that use hardware breakpoints and watchpoints in
> the new gdbarch stuff?

No.  But there is a reason.

The existing h/w breakpoint macros should be moved to the target vector 
and not the architecture vector.  This is because the target, and not 
the architecture, determines the presence of a breakpoint mechanism.

Unfortunatly, so far, no one has made this change, sigh!

Interested?

Andrew

--

e.g., a sim target might support h/w breakpoints when the architecture 
doesn't have the, a native target may not support h/w breakpoints even 
when the architecture does have them.

Re: Hardware Breakpoints

[Peter Jansen]

Hi,

> > I'm trying to use hardware breakpoints in gdb (in the new
> > gdbarchitecture stuff) and cannot figure out how it all works. Are their
> > any gdbarch things for hardware breakpoints and watchpoints?
> >
> > Are there any targets that use hardware breakpoints and watchpoints in
> > the new gdbarch stuff?
> 
> No.  But there is a reason.
> 
> The existing h/w breakpoint macros should be moved to the target vector
> and not the architecture vector.  This is because the target, and not
> the architecture, determines the presence of a breakpoint mechanism.
> 
> Unfortunatly, so far, no one has made this change, sigh!
> 
> Interested?

hmm, I have an embedded target and I connect to it via a JTAG box, so
the target has hardware breakpoints, I assume we need to define them in
avr-tdep.c and put the hooks in the correct place to tie it together? 

What I see at the moment is the breakpoint.c stuff has no connection to
the avr-tdep.c file and I cannot see how to define something in avr-tdep
and let breakpoint.c use it.

Do you have some ideas about how this is supposed to work?

-- 
Peter Jansen
Smart Container
Level 1, NIC Building
Eveleigh
NSW       1430
AUSTRALIA

Re: Hardware Breakpoints

[Andrew Cagney]

> Hi,
> 
> 
>> > I'm trying to use hardware breakpoints in gdb (in the new
>> > gdbarchitecture stuff) and cannot figure out how it all works. Are their
>> > any gdbarch things for hardware breakpoints and watchpoints?
>> >
>> > Are there any targets that use hardware breakpoints and watchpoints in
>> > the new gdbarch stuff?
> 
>> 
>> No.  But there is a reason.
>> 
>> The existing h/w breakpoint macros should be moved to the target vector
>> and not the architecture vector.  This is because the target, and not
>> the architecture, determines the presence of a breakpoint mechanism.
>> 
>> Unfortunatly, so far, no one has made this change, sigh!
>> 
>> Interested?
> 
> 
> hmm, I have an embedded target and I connect to it via a JTAG box, so
> the target has hardware breakpoints, I assume we need to define them in
> avr-tdep.c and put the hooks in the correct place to tie it together? 
> 
> What I see at the moment is the breakpoint.c stuff has no connection to
> the avr-tdep.c file and I cannot see how to define something in avr-tdep
> and let breakpoint.c use it.
> 
> Do you have some ideas about how this is supposed to work?

At this point, things get confusing.  I'll answer the ``supposed to 
work'' question (how it works, is people define those macros).

Two possabilities:

a. You're connecting to a remote target that supports the hardware 
breakpoint/watchpoint mechanism.

GDB just sends h/w breakpoint requests through to the target.  For this 
to work you need to hardwire (:-() up the hw_* functions in remote.c.

(This shouldn't be hardwired.  Instead it should be part of the target 
vector.)

b. Your target doesn't have a remote h/w breakpoint mechanism but does 
have access to the h/w breakpoint registers.

Implements h/w breakpoints locally by directly manipulating the relevant 
registers (i386 does this).  For this to work you hardwire (:-() code in 
your *-tdep.c file to those macros.

(This shouldn't be hardwired either.  Instead, the target vector, 
realising that it can't implement h/w breakpoints directly should ask 
the architecture vector for assistance.)

Andrew