linux-kernel - Re: [patch for 4.0] x86: silence warning in /dev/mem support

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Date:	Fri, 17 Apr 2015 10:39:16 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Pavel Machek <pavel@....cz>
Cc:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	jgross@...e.com, roland@...estorage.com, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch for 4.0] x86: silence warning in /dev/mem support


* Pavel Machek <pavel@....cz> wrote:

> On Thu 2015-04-16 12:09:54, Ingo Molnar wrote:
> > 
> > * Pavel Machek <pavel@....cz> wrote:
> > 
> > > The compiler is right, the code is tricky, but it is also correct
> > > AFAICT.
> > > 
> > > Signed-off-by: Pavel Machek <pavel@....cz>
> > > 
> > > diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
> > > index fdf617c..8a8dce8 100644
> > > --- a/arch/x86/mm/ioremap.c
> > > +++ b/arch/x86/mm/ioremap.c
> > > @@ -341,7 +341,7 @@ void *xlate_dev_mem_ptr(phys_addr_t phys)
> > >  
> > >  	addr = (void __force *)ioremap_cache(start, PAGE_SIZE);
> > >  	if (addr)
> > > -		addr = (void *)((unsigned long)addr | (phys & ~PAGE_MASK));
> > > +		addr = (void *)((unsigned long)addr | (unsigned long) (phys & ~PAGE_MASK));
> > 
> > What warning did it generate and which compiler version?
> 
> 
>   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?

Must have been introduced in:

  4707a341b4af /dev/mem: Use more consistent data types

Thanks,

	Ingo
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