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From: Greg KH <greg@kroah.com>
To: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: kernelnewbies@kernelnewbies.org
Subject: Re: Performing pointer arithmetic on a null pointer?
Date: Thu, 27 May 2021 17:32:11 +0200	[thread overview]
Message-ID: <YK+7e3l/pBEViMht@kroah.com> (raw)
In-Reply-To: <20210527151443.GA138263@hyeyoo>

On Fri, May 28, 2021 at 12:14:43AM +0900, Hyeonggon Yoo wrote:
> Hello, I was compiling kernel with make CC=clang-10 W=1 -s
> 
> there are some places that compiler complains about
> pointer arithmetic like below.it says it's undefined behavior.
> 
> is it just OK to use UBs like this (I hope it's not),
> or am I missing something?
> 
> fs/kernfs/file.c:128:15: warning: performing pointer arithmetic on
> 	a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
>                 return NULL + !*ppos;

Should work just fine, what problems have you found with that code?

Also happens in a few other places in the vfs layer.  Tricky code, but
it works as pointer math is valid C code :)

thanks,

greg k-h

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  parent reply	other threads:[~2021-05-27 15:32 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-27 15:14 Performing pointer arithmetic on a null pointer? Hyeonggon Yoo
2021-05-27 15:27 ` Lukas Bulwahn
2021-05-27 15:56   ` Hyeonggon Yoo
2021-05-27 15:32 ` Greg KH [this message]
2021-05-27 15:49   ` Hyeonggon Yoo

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