Subject: Re: linux-next: build warning after merge of the akpm-current tree

From: Josh Poimboeuf <[email-masked]>
Date: Fri, 29 Apr 2016 09:03:42 -0500

On Fri, Apr 29, 2016 at 08:32:19AM -0500, Josh Poimboeuf wrote:
> On Fri, Apr 29, 2016 at 04:45:43PM +1000, Stephen Rothwell wrote:
> > Hi Andrew,
> > 
> > After merging the akpm-current tree, today's linux-next build (x86_64
> > allmodconfig) produced this warning:
> > 
> > drivers/scsi/ipr.c: In function 'ipr_show_device_id':
> > drivers/scsi/ipr.c:4462:34: warning: format '%llx' expects argument of type 'long long unsigned int', but argument 4 has type 'long unsigned int' [-Wformat=]
> >    len = snprintf(buf, PAGE_SIZE, "0x%llx\n", be64_to_cpu(res->dev_id));
> >                                   ^
> > 
> > Lots and lots like this :-(
> > 
> > Probably introduced by commit
> > 
> >   eef17fb79096 ("byteswap: try to avoid __builtin_constant_p gcc bug")
> > 
> > I guess __builtin_bswap64() has type "unsigned long int" :-(
> 
> Hm, I suppose this is cross-compiled on a powerpc host?
> 
> We probably need to add a (__u64) cast to the return value of
> __builtin_bswap64(), like:
> 
> diff --git a/include/uapi/linux/swab.h b/include/uapi/linux/swab.h
> index de56fd5..d737804 100644
> --- a/include/uapi/linux/swab.h
> +++ b/include/uapi/linux/swab.h
> @@ -123,7 +123,7 @@ static inline __attribute_const__ __u32 __fswahb32(__u32 val)
>   * @x: value to byteswap
>   */
>  #ifdef __HAVE_BUILTIN_BSWAP64__
> -#define __swab64(x) __builtin_bswap64((__u64)(x))
> +#define __swab64(x) (__u64)__builtin_bswap64((__u64)(x))
>  #else
>  #define __swab64(x)				\
>  	(__builtin_constant_p((__u64)(x)) ?	\

Never mind about cross-compiling on powerpc, this has nothing to do with
that.  But the above patch does seem to fix it.

-- 
Josh