linux-kernel - Re: [RFC][PATCH] bitfields API

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Date:	Thu, 28 Aug 2008 22:59:59 +0200
From:	"Vegard Nossum" <vegard.nossum@...il.com>
To:	"Adrian Bunk" <bunk@...nel.org>
Cc:	"Pekka Enberg" <penberg@...helsinki.fi>,
	"Alexey Dobriyan" <adobriyan@...il.com>,
	"David Miller" <davem@...emloft.net>,
	"Ingo Molnar" <mingo@...e.hu>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] bitfields API

On Thu, Aug 28, 2008 at 10:27 PM, Adrian Bunk <bunk@...nel.org> wrote:
> On Thu, Aug 28, 2008 at 09:40:47PM +0300, Pekka Enberg wrote:
>> Hi Alexey,
>>
>> Alexey Dobriyan wrote:
>>> On Thu, Aug 28, 2008 at 08:32:23PM +0200, Vegard Nossum wrote:
>>>> How do you feel about this patch? It's all about making kmemcheck more
>>>> useful... and not much else. Does it have any chance of entering the
>>>> kernel along with kmemcheck (when/if that happens)?
>>>
>>> DEFINE_BITFIELD is horrible.
>>
>> Heh, heh, one alternative is to have a kmemcheck_memset() thingy that
>> unconditionally zeroes bit fields and maybe is a no-op when kmemcheck is
>> disabled.
>
> This sounds as if this might cause bugs to disappear when debugging gets
> turned on?
>
> Or do I miss anything?

You are correct :-)

Almost all the possible solutions (at least the feasible ones) are
trade-offs between false-positives and false-negatives.

So here we are trading a bunch of false-positive errors (a couple of
thousand for transferring a 1M file over ssh :-)) for detecting any
code that uses an uninitialized flag in struct skbuff. So in this case
it is more useful to hide reports about this single bit-field.


Vegard

-- 
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
	-- E. W. Dijkstra, EWD1036
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