From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751575AbeBZUAQ (ORCPT ); Mon, 26 Feb 2018 15:00:16 -0500 Received: from pegase1.c-s.fr ([93.17.236.30]:38983 "EHLO pegase1.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750991AbeBZUAP (ORCPT ); Mon, 26 Feb 2018 15:00:15 -0500 Subject: Re: [PATCH 06/21] powerpc: Avoid comparison of unsigned long >= 0 in __access_ok To: Mathieu Malaterre , Segher Boessenkool Cc: Michael Ellerman , LKML , Paul Mackerras , Jiri Slaby , linuxppc-dev References: <20180225172236.29650-1-malat@debian.org> <20180225172236.29650-7-malat@debian.org> <8862c1e1-d161-3410-1b2a-502ad06cef57@c-s.fr> <6cba215c-127e-f3eb-b525-773b6aed0eb7@c-s.fr> From: christophe leroy Message-ID: <4ddba8bc-b1e5-24a0-602e-672e7b51b203@c-s.fr> Date: Mon, 26 Feb 2018 21:00:09 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le 26/02/2018 à 18:50, Mathieu Malaterre a écrit : > On Mon, Feb 26, 2018 at 8:44 AM, Mathieu Malaterre wrote: >> On Mon, Feb 26, 2018 at 7:50 AM, Christophe LEROY >> wrote: >>> >>> >>> Le 26/02/2018 à 07:34, Christophe LEROY a écrit : >>>> >>>> >>>> >>>> Le 25/02/2018 à 18:22, Mathieu Malaterre a écrit : >>>>> >>>>> Rewrite check size - 1 <= Y as size < Y since `size` is unsigned value. >>>>> Fix warning (treated as error in W=1): >>>>> >>>>> CC arch/powerpc/kernel/signal_32.o >>>>> In file included from ./include/linux/uaccess.h:14:0, >>>>> from ./include/asm-generic/termios-base.h:8, >>>>> from ./arch/powerpc/include/asm/termios.h:20, >>>>> from ./include/uapi/linux/termios.h:6, >>>>> from ./include/linux/tty.h:7, >>>>> from arch/powerpc/kernel/signal_32.c:36: >>>>> ./include/asm-generic/termios-base.h: In function >>>>> ‘user_termio_to_kernel_termios’: >>>>> ./arch/powerpc/include/asm/uaccess.h:52:35: error: comparison of unsigned >>>>> expression >= 0 is always true [-Werror=type-limits] >>>>> (((size) == 0) || (((size) - 1) <= ((segment).seg - (addr))))) >>>>> ^ >>>>> ./arch/powerpc/include/asm/uaccess.h:58:3: note: in expansion of macro >>>>> ‘__access_ok’ >>>>> __access_ok((__force unsigned long)(addr), (size), get_fs())) >>>>> ^~~~~~~~~~~ >>>>> ./arch/powerpc/include/asm/uaccess.h:262:6: note: in expansion of macro >>>>> ‘access_ok’ >>>>> if (access_ok(VERIFY_READ, __gu_addr, (size))) \ >>>>> ^~~~~~~~~ >>>>> ./arch/powerpc/include/asm/uaccess.h:80:2: note: in expansion of macro >>>>> ‘__get_user_check’ >>>>> __get_user_check((x), (ptr), sizeof(*(ptr))) >>>>> ^~~~~~~~~~~~~~~~ >>>>> ./include/asm-generic/termios-base.h:36:6: note: in expansion of macro >>>>> ‘get_user’ >>>>> if (get_user(termios->c_line, &termio->c_line) < 0) >>>>> ^~~~~~~~ >>>>> [...] >>>>> cc1: all warnings being treated as errors >>>>> >>>>> Signed-off-by: Mathieu Malaterre >>>>> --- >>>>> arch/powerpc/include/asm/uaccess.h | 2 +- >>>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>>> >>>>> diff --git a/arch/powerpc/include/asm/uaccess.h >>>>> b/arch/powerpc/include/asm/uaccess.h >>>>> index 51bfeb8777f0..fadc406bd39d 100644 >>>>> --- a/arch/powerpc/include/asm/uaccess.h >>>>> +++ b/arch/powerpc/include/asm/uaccess.h >>>>> @@ -49,7 +49,7 @@ >>>>> #define __access_ok(addr, size, segment) \ >>>>> (((addr) <= (segment).seg) && \ >>>>> - (((size) == 0) || (((size) - 1) <= ((segment).seg - (addr))))) >>>>> + (((size) == 0) || ((size) < ((segment).seg - (addr))))) >>>> >>>> >>>> IIUC, ((2 - 1) <= 1) is the same as (2 < 1) ????? >>> >> >> The whole series was pretty mediocre, but this one was actually pretty >> destructive. Thanks for catching this. >> >>> >>> Note that I already try to submit a fix for this warning 3 years ago >>> (https://patchwork.ozlabs.org/patch/418075/) and it was rejected with the >>> following comment: > > Tested again today with gcc 6.3.0 and gcc is still producing the > original warning (treated as error). That's right, it seems that recent versions of gcc are not happy anymore with that change. Maybe Segher has a suggestion for that one ? > >>> Again, I don't think Linux enables this warning. What did you do to >>> produce this? In any case, it's a bad warning that doesn't take macros >>> into account, and the answer is not to make the code less clear by hiding >>> the fact that zero is a special case. >> >> Right. I'll try to see how to make W=1 run without error with an >> alternate solution. > > So the other alternative is to update a bunch of ppc32 defconfig(s) > with: CONFIG_PPC_DISABLE_WERROR=y. > > Would that be preferable ? No I don't think it is the solution. PPC is built with WERROR in order to catch warnings on real problems. You could disable it selectively when you want to run 'make W=1' and see all possible warnings, then select by yourself which warnings are worth fixing up. Christophe > >>> Christophe >>> >>> >>>> >>>> Christophe >>>> >>>>> #endif >>>>> >>> --- L'absence de virus dans ce courrier électronique a été vérifiée par le logiciel antivirus Avast. https://www.avast.com/antivirus