linux-kernel - Re: [PATCH v3] err.h: allow IS_ERR_VALUE to handle properly more types

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Date:	Thu, 04 Feb 2016 16:00:09 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Andrzej Hajda <a.hajda@...sung.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	open list <linux-kernel@...r.kernel.org>,
	Bob Peterson <rpeterso@...hat.com>
Subject: Re: [PATCH v3] err.h: allow IS_ERR_VALUE to handle properly more types

On Thursday 04 February 2016 15:44:51 Andrzej Hajda wrote:
> On 02/04/2016 01:40 PM, Arnd Bergmann wrote:
> > On Wednesday 03 February 2016 14:15:28 Andrzej Hajda wrote:
> >> diff --git a/include/linux/err.h b/include/linux/err.h
> >> index 56762ab..b7d4a9f 100644
> >> --- a/include/linux/err.h
> >> +++ b/include/linux/err.h
> >> @@ -18,7 +18,9 @@
> >>  
> >>  #ifndef __ASSEMBLY__
> >>  
> >> -#define IS_ERR_VALUE(x) unlikely((x) >= (unsigned long)-MAX_ERRNO)
> >> +#define IS_ERR_VALUE(x) ((typeof(x))(-1) <= 0 \
> >> +                               ? unlikely((x) <= -1) \
> >> +                               : unlikely((x) >= (typeof(x))-MAX_ERRNO))
> >>  
> >>  static inline void * __must_check ERR_PTR(long error)
> >>  {
> >>
> > This has caused a warning to reappear that I had fixed before:
> >
> > fs/gfs2/dir.c: In function 'get_first_leaf':
> > fs/gfs2/dir.c:802:9: warning: 'leaf_no' may be used uninitialized in this function [-Wmaybe-uninitialized]
> >    error = get_leaf(dip, leaf_no, bh_out);
> >          ^
> > fs/gfs2/dir.c: In function 'dir_split_leaf':
> > fs/gfs2/dir.c:1021:8: warning: 'leaf_no' may be used uninitialized in this function [-Wmaybe-uninitialized]
> >   error = get_leaf(dip, leaf_no, &obh);
> 
> What gcc/arch/build options do you use? I cannot reproduce it in my
> environment.
> 

I use an ARM gcc-5.3 with an allmodconfig kernel and CONFIG_CC_OPTIMIZE_FOR_SIZE
disabled. I see the same warning with any gcc version since 4.9, but not earlier.

With the IS_ERR_VALUE() macro I sent, I don't see the warning on any gcc
version. I have now also checked that the behavior on x86 gcc-.4.9 is the
same that I see on ARM (I don't have a large collection of x86 gcc versions
though): same warning with linux-next, no warning with my version or after
reverting your patch.

	Arnd