linux-kernel - Re: [PATCH] parisc: avoid a warning on u8 cast for cmpxchg on u8 pointers

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Message-ID: <20210406105753.GA550515@xiangao.remote.csb>
Date:   Tue, 6 Apr 2021 18:57:53 +0800
From:   Gao Xiang <hsiangkao@...hat.com>
To:     Helge Deller <deller@....de>
Cc:     Gao Xiang <xiang@...nel.org>, linux-parisc@...r.kernel.org,
        Liam Beguin <liambeguin@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] parisc: avoid a warning on u8 cast for cmpxchg on u8
 pointers

On Tue, Apr 06, 2021 at 12:08:55PM +0200, Helge Deller wrote:
> On 4/6/21 6:59 AM, Gao Xiang wrote:
> > From: Gao Xiang <hsiangkao@...hat.com>
> > 
> > commit b344d6a83d01 ("parisc: add support for cmpxchg on u8 pointers")
> > can generate a sparse warningi ("cast truncates bits from constant
> > value"), which has been reported several times [1] [2] [3].
> > 
> > The original code worked as expected, but anyway, let silence such
> > sparse warning as what others did [4].
> > 
> > [1] https://lore.kernel.org/r/202104061220.nRMBwCXw-lkp@intel.com
> > [2] https://lore.kernel.org/r/202012291914.T5Agcn99-lkp@intel.com
> > [3] https://lore.kernel.org/r/202008210829.KVwn7Xeh%25lkp@intel.com
> > [4] https://lore.kernel.org/r/20210315131512.133720-2-jacopo+renesas@jmondi.org
> > Cc: Liam Beguin <liambeguin@...il.com>
> > Cc: Helge Deller <deller@....de>
> > Signed-off-by: Gao Xiang <hsiangkao@...hat.com>
> 
> applied to the parisc for-next git tree.
> (I fixed up the typo above too)

Thanks all! :)

Thanks,
Gao Xiang

> 
> Thanks!
> Helge
> 
> > ---
> >   arch/parisc/include/asm/cmpxchg.h | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/arch/parisc/include/asm/cmpxchg.h b/arch/parisc/include/asm/cmpxchg.h
> > index cf5ee9b0b393..84ee232278a6 100644
> > --- a/arch/parisc/include/asm/cmpxchg.h
> > +++ b/arch/parisc/include/asm/cmpxchg.h
> > @@ -72,7 +72,7 @@ __cmpxchg(volatile void *ptr, unsigned long old, unsigned long new_, int size)
> >   #endif
> >   	case 4: return __cmpxchg_u32((unsigned int *)ptr,
> >   				     (unsigned int)old, (unsigned int)new_);
> > -	case 1: return __cmpxchg_u8((u8 *)ptr, (u8)old, (u8)new_);
> > +	case 1: return __cmpxchg_u8((u8 *)ptr, old & 0xff, new_ & 0xff);
> >   	}
> >   	__cmpxchg_called_with_bad_pointer();
> >   	return old;
> > 
>