linux-kernel - Re: [PATCH] ptrdiff_t is not uintptr

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Message-ID: <20070820005743.GY21089@ftp.linux.org.uk>
Date:	Mon, 20 Aug 2007 01:57:43 +0100
From:	Al Viro <viro@....linux.org.uk>
To:	Anton Altaparmakov <aia21@....ac.uk>
Cc:	David Brownell <david-b@...bell.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ptrdiff_t is not uintptr_t, damnit

On Mon, Aug 20, 2007 at 01:29:21AM +0100, Anton Altaparmakov wrote:
> Hi,
> 
> On 20 Aug 2007, at 01:19, David Brownell wrote:
> >On Sunday 19 August 2007, Al Viro wrote:
> >>is wrong; for one thing, it's a bad C (it's what uintptr_t is for;  
> >>in general
> >>we are not even promised that ptrdiff_t is large enough to hold a  
> >>pointer,
> >
> >ISTR we don't *have* a uintptr_t on all architectures, or that would
> >be the appropriate thing to use in these 32/64 bit ABI scenarios.
> >
> >
> >>Use unsigned long or uintptr_t instead.
> >
> >I suspect you mean "unsigned long long"...
> 
> No he doesn't.  "unsigned long" is guaranteed to be large enough to  
> hold a pointer (at least on Linux anyway).
> 
> On a 32-bit arch "unsigned long" is 32-bit and pointers are 32-bit.

... while unsigned long long is 64bit, which is definitely not what
one wants.  For sparse it's "unsigned long is special".

FWIW, this patch puts it in linux/types.h as unsigned long.  Eventually
we might want to switch explicit casts to/from unsigned long in such contexts
to uintptr_t, but for now we can't start complaining about unsigned long -
too many places are using it.  I'll see what can be done to get sane
assistance from sparse in that kind of work...

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