From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f193.google.com ([209.85.220.193]:46428 "EHLO mail-qk0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932903AbeCJHEJ (ORCPT ); Sat, 10 Mar 2018 02:04:09 -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 08:03:47 +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 7:10 AM, Miguel Ojeda wrote: > 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. > Just compiled 4.9.0 and it seems to work -- so that would be the minimum required. Sigh... Some enterprise distros are either already shipping gcc >= 5 or will probably be shipping it soon (e.g. RHEL 8), so how much does it hurt to ask for a newer gcc? Are there many users/companies out there using enterprise distributions' gcc to compile and run the very latest kernels? Miguel