From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH v2] byteswap: try to avoid __builtin_constant_p gcc bug Date: Tue, 03 May 2016 08:36:53 +0200 Message-ID: <12243652.bxSxEgjgfk@wuerfel> References: <1780465.XdtPJpi8Tt@wuerfel> <2346484.tQ1Ts8bYKc@wuerfel> <20160502163225.8b00a5ef7170a0f2533438e9@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20160502163225.8b00a5ef7170a0f2533438e9@linux-foundation.org> Sender: linux-kernel-owner@vger.kernel.org To: Andrew Morton Cc: mm-commits@vger.kernel.org, linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org, jpoimboe@redhat.com, Martin Jambor , "Martin K. Petersen" , James Bottomley , Denys Vlasenko , Thomas Graf , Peter Zijlstra , David Rientjes , Ingo Molnar , Himanshu Madhani , Dept-Eng QLA2xxx Upstream , Jan Hubicka List-Id: linux-scsi@vger.kernel.org On Monday 02 May 2016 16:32:25 Andrew Morton wrote: > On Tue, 03 May 2016 01:10:16 +0200 Arnd Bergmann wrot= e: >=20 > > On Monday 02 May 2016 16:02:18 Andrew Morton wrote: > > > On Mon, 02 May 2016 23:48:19 +0200 Arnd Bergmann = wrote: > > >=20 > > > > This is another attempt to avoid a regression in wwn_to_u64() a= fter > > > > that started using get_unaligned_be64(), which in turn ran into= a > > > > bug on gcc-4.9 through 6.1. > > >=20 > > > I'm still getting a couple screenfuls of things like > > >=20 > > > net/tipc/name_distr.c: In function 'tipc_named_process_backlog': > > > net/tipc/name_distr.c:330: warning: format '%u' expects type 'uns= igned int', but argument 3 has type 'unsigned int' > > > net/tipc/name_distr.c:330: warning: format '%u' expects type 'uns= igned int', but argument 4 has type 'unsigned int' > > > net/tipc/name_distr.c:330: warning: format '%u' expects type 'uns= igned int', but argument 5 has type 'unsigned int' > > > net/tipc/name_distr.c:330: warning: format '%u' expects type 'uns= igned int', but argument 7 has type 'unsigned int' > >=20 > > I've built a few thousand kernels (arm32 with gcc-6.1) with the pat= ch applied, > > but didn't see this one. What target architecture and compiler vers= ion produced > > this? Does it go away if you add a (__u32) cast? I don't even know = what the > > warning is trying to tell me. >=20 > heh, I didn't actually read it. >=20 > Hopefully we can write this off as a gcc-4.4.4 glitch. 4.8.4 is OK. Ah, old compiler. I've tried gcc-4.3 now on ARM, and I don't get this w= arning (just a lot "may be used uninitialized"), but unlike gcc-4.4, my versio= n doesn't actually get into the code path I have changed because __builtin_bswap3= 2 was only introduced with 4.4. I don't have gcc-4.4 and 4.5 here, but the warning does show up with 4.= 6, 4.7 and 4.8: drivers/soc/sunxi/sunxi_sram.c: In function =E2=80=98sunxi_sram_show=E2= =80=99: drivers/soc/sunxi/sunxi_sram.c:103:7: warning: format =E2=80=98%x=E2=80= =99 expects argument of type =E2=80=98unsigned int=E2=80=99, but argume= nt 3 has type =E2=80=98unsigned int=E2=80=99 [-Wformat=3D] 4.8 is probably still common enough that we should try to address this. This change addresses the problem for me with ARM gcc-4.8, but adding two more type casts. This also makes the 16/32/64 bit swaps all look the same. I would expect this to also have the same effect on 4.4. Please fold into the previous patch. Signed-off-by: Arnd Bergmann diff --git a/include/uapi/linux/swab.h b/include/uapi/linux/swab.h index d737804af181..8f3a8f606fd9 100644 --- a/include/uapi/linux/swab.h +++ b/include/uapi/linux/swab.h @@ -97,7 +97,7 @@ static inline __attribute_const__ __u32 __fswahb32(__= u32 val) * @x: value to byteswap */ #ifdef __HAVE_BUILTIN_BSWAP16__ -#define __swab16(x) __builtin_bswap16((__u16)(x)) +#define __swab16(x) (__u16)__builtin_bswap16((__u16)(x)) #else #define __swab16(x) \ (__builtin_constant_p((__u16)(x)) ? \ @@ -110,7 +110,7 @@ static inline __attribute_const__ __u32 __fswahb32(= __u32 val) * @x: value to byteswap */ #ifdef __HAVE_BUILTIN_BSWAP32__ -#define __swab32(x) __builtin_bswap32((__u32)(x)) +#define __swab32(x) (__u32)__builtin_bswap32((__u32)(x)) #else #define __swab32(x) \ (__builtin_constant_p((__u32)(x)) ? \