From 57e86fa16a707db9e05dec77eb88a398f05a022b Mon Sep 17 00:00:00 2001 From: chenqiwu Date: Thu, 4 Jun 2020 16:48:55 -0700 Subject: [PATCH] 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") [akpm@linux-foundation.org: fix build] Signed-off-by: chenqiwu Signed-off-by: Andrew Morton Reviewed-by: Andrew Morton Reviewed-by: Wei Yang Cc: Matthew Wilcox Cc: David Hildenbrand Cc: Michal Hocko Cc: Pankaj Gupta Cc: Yang Shi Cc: Qian Cai Cc: Baoquan He Link: http://lkml.kernel.org/r/1586599916-15456-1-git-send-email-qiwuchen55@gmail.com Signed-off-by: Linus Torvalds --- include/linux/mm.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 5bfc36320e3c..1744081a34d4 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1726,7 +1726,7 @@ 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 */ };