linux-kernel - Re: [PATCH v5 01/38] minmax: Add in

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Message-Id: <20230711084958.8fdbb0fc4f80c6d9bbaf0ca3@linux-foundation.org>
Date:   Tue, 11 Jul 2023 08:49:58 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 01/38] minmax: Add in_range() macro

On Tue, 11 Jul 2023 03:14:44 +0100 Matthew Wilcox <willy@...radead.org> wrote:

> On Mon, Jul 10, 2023 at 04:13:41PM -0700, Andrew Morton wrote:
> > > +/**
> > > + * in_range - Determine if a value lies within a range.
> > > + * @val: Value to test.
> > > + * @start: First value in range.
> > > + * @len: Number of values in range.
> > > + *
> > > + * This is more efficient than "if (start <= val && val < (start + len))".
> > > + * It also gives a different answer if @start + @len overflows the size of
> > > + * the type by a sufficient amount to encompass @val.  Decide for yourself
> > > + * which behaviour you want, or prove that start + len never overflow.
> > > + * Do not blindly replace one form with the other.
> > > + */
> > > +#define in_range(val, start, len)					\
> > > +	sizeof(start) <= sizeof(u32) ? in_range32(val, start, len) :	\
> > > +		in_range64(val, start, len)
> > 
> > There's nothing here to prevent callers from passing a mixture of
> > 32-bit and 64-bit values, possibly resulting in truncation of `val' or
> > `len'.
> > 
> > Obviously caller is being dumb, but I think it's cost-free to check all
> > three of the arguments for 64-bitness?
> > 
> > Or do a min()/max()-style check for consistently typed arguments?
> 
> How about
> 
> #define in_range(val, start, len)					\
> 	(sizeof(val) | sizeof(start) | size(len)) <= sizeof(u32) ?	\
> 		in_range32(val, start, len) : in_range64(val, start, len)

It saves some typing ;)   sizeof(val+start+len)?  <no>