linux-kernel - Re: [RFC][PATCH] A generic boolean (version 6)

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Message-Id: <1153978047.2807.5.camel@entropy>
Date:	Wed, 26 Jul 2006 22:27:27 -0700
From:	Nicholas Miell <nmiell@...cast.net>
To:	Arnd Bergmann <arnd.bergmann@...ibm.com>
Cc:	ricknu-0@...dent.ltu.se, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...l.org>, Jeff Garzik <jeff@...zik.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Vadim Lobanov <vlobanov@...akeasy.net>,
	Jan Engelhardt <jengelh@...ux01.gwdg.de>,
	Shorty Porty <getshorty_@...mail.com>,
	Peter Williams <pwil3058@...pond.net.au>,
	Michael Buesch <mb@...sch.de>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Stefan Richter <stefanr@...6.in-berlin.de>, larsbj@...lik.net,
	Paul Jackson <pj@....com>
Subject: Re: [RFC][PATCH] A generic boolean (version 6)

On Thu, 2006-07-27 at 04:48 +0200, Arnd Bergmann wrote:
> On Wednesday 26 July 2006 22:28, ricknu-0@...dent.ltu.se wrote:
> > Have not found any (real) reason letting the cpp know about false/true. As I
> > said in the last version, the only reason seem to be for the userspace. Well, as
> > there is no program of my knowlage that needs it, they were removed.
> > 
> If we don't expect this to show up in the ABI (which I hope is true), then
> the definition should probably be inside of #ifdef __KERNEL__. Right
> now, it's inside of (!__KERNEL_STRICT_NAMES), which is not exactly the
> same.
> 

If _Bool does end up in the user-kernel ABI, be advised that validating
them will be tricky ("b == true || b == false" or "!!b" won't work), and
the compiler could in theory generate code which tests truthfulness by
comparing to 1 in one place and non-zero in another.

My brief IRC conversation with gcc people regarding validating untrusted
_Bool resulted in the instruction to never store a value in a _Bool
until after it has been validated. 

-- 
Nicholas Miell <nmiell@...cast.net>

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