Re: [PATCH 09/19] x86, mpx: trace entry to bounds exception paths

Thomas Gleixner
2015-05-18T23:35:24Z

On Mon, 18 May 2015, Dave Hansen wrote:

> On 05/18/2015 01:58 PM, Thomas Gleixner wrote:
> > On Fri, 8 May 2015, Dave Hansen wrote:
> >> > This patch adds a trace point for the case where we are
> >> > passing the exception up to userspace with a signal.
> >> >
> >> > We are also explicit that we're printing out the inverse of
> >> > the 'upper' that we encounter. If you want to filter, for
> >> > instance, you need to ~ the value first.
> > Confused. What is the point of printing the complement of upper?
>
> If a pointer's range is
>
> 0x1000 -> 0x2000
>
> it is stored in the bounds table as (32-bits here for brevity):
>
> lower: 0x00001000
> upper: 0xffffdfff
>
> That is so that an all 0's entry:
>
> lower: 0x00000000
> upper: 0x00000000
>
> corresponds to the "init" bounds which store a *range* of:
>
> 0x00000000 -> 0xffffffff
>
> The 'upper' stored in the table is gibberish to print by itself, so we
> print ~upper to get the *actual*, logical value.

Some comment in the code and the changelog might be helpful then :)

Thanks,

tglx