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From: Denis Vlasenko <vda@ilport.com.ua>
To: Arjan van de Ven <arjan@infradead.org>
Subject: Re: [-mm patch] make kcalloc() a static inline
Date: Mon, 15 Aug 2005 11:20:46 +0300
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Cc: Adrian Bunk <bunk@stusta.de>, Pekka J Enberg <penberg@cs.Helsinki.FI>,
       Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org
References: <20050808223842.GM4006@stusta.de> <200508151106.05973.vda@ilport.com.ua> <1124093660.3228.14.camel@laptopd505.fenrus.org>
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On Monday 15 August 2005 11:14, Arjan van de Ven wrote:
> On Mon, 2005-08-15 at 11:06 +0300, Denis Vlasenko wrote:
> 
> > > +static inline void *kcalloc(size_t n, size_t size, unsigned int __nocast flags)
> > > +{
> > > +	if (n != 0 && size > INT_MAX / n)
> > > +		return NULL;
> > > +	return kzalloc(n * size, flags);
> > > +}
> 
> > Can you conditionalize it on __builtin_constant_p(n) ?
> > Otherwise with variable n you have 3 oprations in inlined
> > code, one of them a division.
> 
> you can't conditionalize the security check really. If it's constant,
> gcc will optimize it anyway, and if it's not constant you for sure want
> the check there...

Sure, I don't want to disable the check. I want that check to be
in _non-inlined function_.

static inline void *kcalloc(size_t n, size_t size, unsigned int __nocast flags)
{
	if (__builtin_constant_p(n)) {
		if (n != 0 && size > INT_MAX / n)
			return NULL;
		return kzalloc(n * size, flags);
	}
	return kcalloc_helper(n, size, flags);
}

void *kcalloc_helper(size_t n, size_t size, unsigned int __nocast flags)
{
	if (n != 0 && size > INT_MAX / n)
		return NULL;
	return kzalloc(n * size, flags);
}
--
vda