On Sat, Apr 27, 2013 at 07:34:24PM +0200, Oleg Nesterov wrote:
> On 04/27, Oleg Nesterov wrote:
> >
> > On 04/26, Jacob Shin wrote:
> > >
> > > @@ -518,12 +518,10 @@ int parse_events_add_breakpoint(struct list_head
> > > **list, int *idx,
> > > if (parse_breakpoint_type(type, &attr))
> > > return -EINVAL;
> > >
> > > - /*
> > > - * We should find a nice way to override the access length
> > > - * Provide some defaults for now
> > > - */
> > > if (attr.bp_type == HW_BREAKPOINT_X)
> > > attr.bp_len = sizeof(long);
> > > + else if (len)
> > > + attr.bp_len = len;
> > > else
> > > attr.bp_len = HW_BREAKPOINT_LEN_4;
> >
> > Stupid question... So X86_FEATURE_BPEXT only works for r/w? I mean, it
> > doesn't allow to specify the mask for an execute breakpoint?
Yes, it does work with instruction execution breakpoints as well.
> >
> > Otherwise the code above should be probably updated, say,
> >
> > if (!len) {
> > len = attr.bp_type == HW_BREAKPOINT_X ?
> > sizeof(long) : HW_BREAKPOINT_LEN_4;
> > }
> > attr.bp_len = len;
>
> OK, we can't do this until we change arch_build_bp_info() which
> insists on sizeof(long) and sets X86_BREAKPOINT_LEN_X == 1.
Right, for instruction execution breakpoints, it is a x86 requirement
to have length as 1. Which makes sense, because you really want to be
trapping on 1 specifc IP.
Now using this new mask MSR, we should be able to trap on range of IPs,
but yeah since we are naturally extending bp_len .... we'll tackle it
later when we can come up with a good scheme to express masks in arch
neutral/general way.
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