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Date: Mon, 20 Apr 2015 08:52:35 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Pavel Machek <pavel@ucw.cz>
Cc: tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, jgross@suse.com,
        roland@purestorage.com, akpm@linux-foundation.org,
        linux-kernel@vger.kernel.org
Subject: Re: [patch for 4.0] x86: silence warning in /dev/mem support
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* Pavel Machek <pavel@ucw.cz> wrote:

> Hi!
> 
> > >   CC      arch/x86/mm/ioremap.o
> > >   arch/x86/mm/ioremap.c: In function ‘xlate_dev_mem_ptr’:
> > >   arch/x86/mm/ioremap.c:363:10: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
> > >      addr = (void *)((unsigned long)addr | (phys & ~PAGE_MASK));
> > >                ^
> > >   LD      arch/x86/mm/built-in.o
> > > 		 
> > > pavel@amd:/data/l/linux$ gcc --version
> > > gcc (Debian 4.9.2-10) 4.9.2
> > 
> > So this code has not been changed for a year or so in theory, and I've 
> > never seen this warning with GCC 4.9.1. I'm wondering how it 
> > triggered. Could you send me your .config that triggers this?
> 
> Config sent in private email. 32-bit kernel.

Ah, I see, the key is:

  CONFIG_HIGHMEM64G=y

and neither x86 defconfig nor allyesconfig/allmodconfig selects 
HIGHMEM64G apparently, so this was rarely triggered.

Thanks,

	Ingo