linux-kernel - Re: [PATCH] tools/nolibc: avoid using plain integer as NULL pointer

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Message-ID: <20251110121622.3a8e4a40@pumpkin>
Date: Mon, 10 Nov 2025 12:16:22 +0000
From: David Laight <david.laight.linux@...il.com>
To: Willy Tarreau <w@....eu>
Cc: Thomas Weißschuh <linux@...ssschuh.net>,
 linux-kernel@...r.kernel.org, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] tools/nolibc: avoid using plain integer as NULL pointer

On Sun, 9 Nov 2025 20:57:54 +0100
Willy Tarreau <w@....eu> wrote:

> Hi Thomas,
> 
> On Sun, Nov 09, 2025 at 08:27:29PM +0100, Thomas Weißschuh wrote:
> > The integer zero should not be used as NULL pointer.
> > It is invalid and sparse will complain about it.
> > 
> > Use proper NULL pointers instead.  
> 
> Huh ? I've been using that for decades and seeing it everywhere. That's
> quite bizarre, 0 is perfectly valid as a pointer. Ah, here it is, in
> C99:6.3.2.3:
> 
>   An integer constant expression with the value 0, or such an expression
>   cast to type void *, is called a null pointer constant.

Note also that the above is true even if the value stored in memory for
a NULL point isn't the 'all zero' bit pattern.

The only time it actually matters whether you use 0 or NULL is in varargs
function calls.
Even that is dependant on the calling convention (when NULL is zero).

	David