From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f196.google.com ([209.85.216.196]:41518 "EHLO mail-qt0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750858AbeCJGLJ (ORCPT ); Sat, 10 Mar 2018 01:11:09 -0500 MIME-Version: 1.0 In-Reply-To: References: <20180309200536.GA5670@beast> <20180309160719.154a3158e2d8ee56e43a918f@linux-foundation.org> From: Miguel Ojeda Date: Sat, 10 Mar 2018 07:10:47 +0100 Message-ID: Subject: Re: [PATCH v3] kernel.h: Skip single-eval logic on literals in min()/max() To: Randy Dunlap Cc: Andrew Morton , Kees Cook , linux-kernel , Josh Poimboeuf , Rasmus Villemoes , "Gustavo A. R. Silva" , "Tobin C. Harding" , Steven Rostedt , Jonathan Corbet , Chris Mason , Josef Bacik , David Sterba , "David S. Miller" , Alexey Kuznetsov , Hideaki YOSHIFUJI , Ingo Molnar , Peter Zijlstra , Thomas Gleixner , Masahiro Yamada , Borislav Petkov , Ian Abbott , Sergey Senozhatsky , Petr Mladek , Andy Shevchenko , Pantelis Antoniou , Linux Btrfs , Network Development , Kernel Hardening , Linus Torvalds Content-Type: text/plain; charset="UTF-8" Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Sat, Mar 10, 2018 at 4:11 AM, Randy Dunlap wrote: > On 03/09/2018 04:07 PM, Andrew Morton wrote: >> On Fri, 9 Mar 2018 12:05:36 -0800 Kees Cook wrote: >> >>> When max() is used in stack array size calculations from literal values >>> (e.g. "char foo[max(sizeof(struct1), sizeof(struct2))]", the compiler >>> thinks this is a dynamic calculation due to the single-eval logic, which >>> is not needed in the literal case. This change removes several accidental >>> stack VLAs from an x86 allmodconfig build: >>> >>> $ diff -u before.txt after.txt | grep ^- >>> -drivers/input/touchscreen/cyttsp4_core.c:871:2: warning: ISO C90 forbids variable length array ‘ids’ [-Wvla] >>> -fs/btrfs/tree-checker.c:344:4: warning: ISO C90 forbids variable length array ‘namebuf’ [-Wvla] >>> -lib/vsprintf.c:747:2: warning: ISO C90 forbids variable length array ‘sym’ [-Wvla] >>> -net/ipv4/proc.c:403:2: warning: ISO C90 forbids variable length array ‘buff’ [-Wvla] >>> -net/ipv6/proc.c:198:2: warning: ISO C90 forbids variable length array ‘buff’ [-Wvla] >>> -net/ipv6/proc.c:218:2: warning: ISO C90 forbids variable length array ‘buff64’ [-Wvla] >>> >>> Based on an earlier patch from Josh Poimboeuf. >> >> v1, v2 and v3 of this patch all fail with gcc-4.4.4: >> >> ./include/linux/jiffies.h: In function 'jiffies_delta_to_clock_t': >> ./include/linux/jiffies.h:444: error: first argument to '__builtin_choose_expr' not a constant > > > I'm seeing that problem with >> gcc --version > gcc (SUSE Linux) 4.8.5 Same here, 4.8.5 fails. gcc 5.4.1 seems to work. I compiled a minimal 5.1.0 and it seems to work as well. Cheers, Miguel From mboxrd@z Thu Jan 1 00:00:00 1970 From: Miguel Ojeda Subject: Re: [PATCH v3] kernel.h: Skip single-eval logic on literals in min()/max() Date: Sat, 10 Mar 2018 07:10:47 +0100 Message-ID: References: <20180309200536.GA5670@beast> <20180309160719.154a3158e2d8ee56e43a918f@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Cc: Andrew Morton , Kees Cook , linux-kernel , Josh Poimboeuf , Rasmus Villemoes , "Gustavo A. R. Silva" , "Tobin C. Harding" , Steven Rostedt , Jonathan Corbet , Chris Mason , Josef Bacik , David Sterba , "David S. Miller" , Alexey Kuznetsov , Hideaki YOSHIFUJI , Ingo Molnar , Peter Zijlstra , Thomas Gleixner , Masahiro Yamada , Borislav Petkov Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Sat, Mar 10, 2018 at 4:11 AM, Randy Dunlap wrote= : > On 03/09/2018 04:07 PM, Andrew Morton wrote: >> On Fri, 9 Mar 2018 12:05:36 -0800 Kees Cook wrot= e: >> >>> When max() is used in stack array size calculations from literal values >>> (e.g. "char foo[max(sizeof(struct1), sizeof(struct2))]", the compiler >>> thinks this is a dynamic calculation due to the single-eval logic, whic= h >>> is not needed in the literal case. This change removes several accident= al >>> stack VLAs from an x86 allmodconfig build: >>> >>> $ diff -u before.txt after.txt | grep ^- >>> -drivers/input/touchscreen/cyttsp4_core.c:871:2: warning: ISO C90 forbi= ds variable length array =E2=80=98ids=E2=80=99 [-Wvla] >>> -fs/btrfs/tree-checker.c:344:4: warning: ISO C90 forbids variable lengt= h array =E2=80=98namebuf=E2=80=99 [-Wvla] >>> -lib/vsprintf.c:747:2: warning: ISO C90 forbids variable length array = =E2=80=98sym=E2=80=99 [-Wvla] >>> -net/ipv4/proc.c:403:2: warning: ISO C90 forbids variable length array = =E2=80=98buff=E2=80=99 [-Wvla] >>> -net/ipv6/proc.c:198:2: warning: ISO C90 forbids variable length array = =E2=80=98buff=E2=80=99 [-Wvla] >>> -net/ipv6/proc.c:218:2: warning: ISO C90 forbids variable length array = =E2=80=98buff64=E2=80=99 [-Wvla] >>> >>> Based on an earlier patch from Josh Poimboeuf. >> >> v1, v2 and v3 of this patch all fail with gcc-4.4.4: >> >> ./include/linux/jiffies.h: In function 'jiffies_delta_to_clock_t': >> ./include/linux/jiffies.h:444: error: first argument to '__builtin_choos= e_expr' not a constant > > > I'm seeing that problem with >> gcc --version > gcc (SUSE Linux) 4.8.5 Same here, 4.8.5 fails. gcc 5.4.1 seems to work. I compiled a minimal 5.1.0 and it seems to work as well. Cheers, Miguel