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

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Message-ID: <alpine.DEB.2.11.1505182246290.4225@nanos>
Date:	Mon, 18 May 2015 22:58:34 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Dave Hansen <dave@...1.net>
cc:	linux-kernel@...r.kernel.org, x86@...nel.org,
	dave.hansen@...ux.intel.com
Subject: Re: [PATCH 09/19] x86, mpx: trace entry to bounds exception paths

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?

Lets assume that my boundaries are: lower = 0x10000 upper = 0x1ffff

So the trace will tell me:

  pointer: 0x40000 lower: 0x10000 ~upper: 0xfffffffffff70000

Even if the upper bound is not inclusive (and I can't be bothered to
look it up right now), i.e. in the example above upper = 0x20000 we
would get

  pointer: 0x40000 lower: 0x10000 ~upper: 0xfffffffffffdffff

I have a hard time to understand the value of this over:

  pointer: 0x40000 lower: 0x10000 upper: 0x20000

Thanks,

	tglx


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