From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f69.google.com (mail-pg0-f69.google.com [74.125.83.69]) by kanga.kvack.org (Postfix) with ESMTP id B78236B0390 for ; Tue, 28 Mar 2017 19:29:45 -0400 (EDT) Received: by mail-pg0-f69.google.com with SMTP id 79so129591281pgf.2 for ; Tue, 28 Mar 2017 16:29:45 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id e3si5377865plj.114.2017.03.28.16.29.44 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 28 Mar 2017 16:29:44 -0700 (PDT) Date: Tue, 28 Mar 2017 16:29:42 -0700 From: Andrew Morton Subject: Re: [PATCH] kasan: avoid -Wmaybe-uninitialized warning Message-Id: <20170328162942.eb08b50af725428a4be25f2b@linux-foundation.org> In-Reply-To: <20170323150415.301180-1-arnd@arndb.de> References: <20170323150415.301180-1-arnd@arndb.de> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Arnd Bergmann Cc: Andrey Ryabinin , Alexander Potapenko , Dmitry Vyukov , Andrey Konovalov , Peter Zijlstra , kasan-dev@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Thu, 23 Mar 2017 16:04:09 +0100 Arnd Bergmann wrote: > gcc-7 produces this warning: > > mm/kasan/report.c: In function 'kasan_report': > mm/kasan/report.c:351:3: error: 'info.first_bad_addr' may be used uninitialized in this function [-Werror=maybe-uninitialized] > print_shadow_for_address(info->first_bad_addr); > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > mm/kasan/report.c:360:27: note: 'info.first_bad_addr' was declared here > > The code seems fine as we only print info.first_bad_addr when there is a shadow, > and we always initialize it in that case, but this is relatively hard > for gcc to figure out after the latest rework. Adding an intialization > in the other code path gets rid of the warning. > > ... > > --- a/mm/kasan/report.c > +++ b/mm/kasan/report.c > @@ -109,6 +109,8 @@ const char *get_wild_bug_type(struct kasan_access_info *info) > { > const char *bug_type = "unknown-crash"; > > + info->first_bad_addr = (void *)(-1ul); > + > if ((unsigned long)info->access_addr < PAGE_SIZE) > bug_type = "null-ptr-deref"; > else if ((unsigned long)info->access_addr < TASK_SIZE) A weird, ugly and seemingly-unneeded statement should have a comment explaining its existence, no? Fortunately it is no longer needed. We now have: static void print_error_description(struct kasan_access_info *info) { const char *bug_type = "unknown-crash"; u8 *shadow_addr; info->first_bad_addr = find_first_bad_addr(info->access_addr, info->access_size); shadow_addr = (u8 *)kasan_mem_to_shadow(info->first_bad_addr); ... -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org