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

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Date:	Tue, 19 May 2015 01:35:31 +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 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

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