From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: + mm-replace-zero-length-array-with-flexible-array-member.patch added to -mm tree Date: Mon, 13 Apr 2020 15:33:02 -0700 Message-ID: <20200413223302.JSM1HaXea%akpm@linux-foundation.org> References: <20200412004155.1a8f4e081b4e03ef5903abb5@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Return-path: Received: from mail.kernel.org ([198.145.29.99]:34186 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389641AbgDMWdD (ORCPT ); Mon, 13 Apr 2020 18:33:03 -0400 In-Reply-To: <20200412004155.1a8f4e081b4e03ef5903abb5@linux-foundation.org> Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: akpm@linux-foundation.org, bhe@redhat.com, cai@lca.pw, chenqiwu@xiaomi.com, david@redhat.com, mhocko@suse.com, mm-commits@vger.kernel.org, pankaj.gupta.linux@gmail.com, richard.weiyang@gmail.com, willy@infradead.org, yang.shi@linux.alibaba.com Archived-At: List-Archive: List-Post: The patch titled Subject: mm: replace zero-length array with flexible-array member has been added to the -mm tree. Its filename is mm-replace-zero-length-array-with-flexible-array-member.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/mm-replace-zero-length-array-with-flexible-array-member.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/mm-replace-zero-length-array-with-flexible-array-member.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: chenqiwu Subject: mm: replace zero-length array with flexible-array member The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Link: http://lkml.kernel.org/r/1586599916-15456-1-git-send-email-qiwuchen55@gmail.com Signed-off-by: chenqiwu Reviewed-by: Andrew Morton Cc: Matthew Wilcox Cc: David Hildenbrand Cc: Wei Yang Cc: Michal Hocko Cc: Pankaj Gupta Cc: Yang Shi Cc: Qian Cai Cc: Baoquan He Signed-off-by: Andrew Morton --- include/linux/mm.h | 2 +- include/linux/mmzone.h | 2 +- include/linux/swap.h | 2 +- 3 files changed, 3 insertions(+), 3 deletions(-) --- a/include/linux/mm.h~mm-replace-zero-length-array-with-flexible-array-member +++ a/include/linux/mm.h @@ -1718,7 +1718,7 @@ struct frame_vector { unsigned int nr_frames; /* Number of frames stored in ptrs array */ bool got_ref; /* Did we pin pages by getting page ref? */ bool is_pfns; /* Does array contain pages or pfns? */ - void *ptrs[0]; /* Array of pinned pfns / pages. Use + void *ptrs[]; /* Array of pinned pfns / pages. Use * pfns_vector_pages() or pfns_vector_pfns() * for access */ }; --- a/include/linux/mmzone.h~mm-replace-zero-length-array-with-flexible-array-member +++ a/include/linux/mmzone.h @@ -1147,7 +1147,7 @@ struct mem_section_usage { DECLARE_BITMAP(subsection_map, SUBSECTIONS_PER_SECTION); #endif /* See declaration of similar field in struct zone */ - unsigned long pageblock_flags[0]; + unsigned long pageblock_flags[]; }; void subsection_map_init(unsigned long pfn, unsigned long nr_pages); --- a/include/linux/swap.h~mm-replace-zero-length-array-with-flexible-array-member +++ a/include/linux/swap.h @@ -275,7 +275,7 @@ struct swap_info_struct { */ struct work_struct discard_work; /* discard worker */ struct swap_cluster_list discard_clusters; /* discard clusters list */ - struct plist_node avail_lists[0]; /* + struct plist_node avail_lists[]; /* * entries in swap_avail_heads, one * entry per node. * Must be last as the number of the _ Patches currently in -mm which might be from chenqiwu@xiaomi.com are mm-swapfile-use-list_prevnext_entry-instead-of-open-coding.patch mm-replace-zero-length-array-with-flexible-array-member.patch