Re: Hardware watchpoint for read

[Luis Gustavo <luis_gustavo at mentor dot com>]

On 04/24/2012 10:15 AM, Xin Tong wrote:
> On Tue, Apr 24, 2012 at 9:09 AM, Luis Gustavo<luis_gustavo@mentor.com>  wrote:
> > Hi,
> >
> >
> > On 04/24/2012 10:02 AM, Xin Tong wrote:
> > > Hello
> > >
> > > I am wondering that can gdb insert hardware watch point for read to
> > > the watched memory ? can other debugger do that ? is it supported in
> > > hardware watchpoint ?
> > >
> > > Thanks
> > >
> > > Xin
> >
> > Read watchpoints are hard to implement as soft-watchpoints, so they're
> > usually implemented as hardware watchpoints.
>
> software write watchpoint is easier to implement ? do not software
> watchpoint need to watch all memory accesses (read and write) to a
> memory location in software ?

Writes are "easier" to implemenet due to the fact that they usually 
change memory contents. Reads don't.

> > If a debugger knows how to properly set the bits in the hardware, either
> > through ptrace or other means, it can configure a read/write/read-write
> > watchpoint. Depends on hardware support really.
>
> do you know whether this is supported on the x86 chips ? is thee a way
> to try this out in gdb ?

All those modes should be supported in x86. Try "watch", "rwatch" and 
"awatch".

> > Regards,
> > Luis