From 3c2faf61fb7152dc1526402bf96ff705f15c0b6b Mon Sep 17 00:00:00 2001 From: "Gustavo A. R. Silva" Date: Thu, 27 Feb 2020 12:48:08 -0600 Subject: [PATCH] char: mspec: 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") Signed-off-by: Gustavo A. R. Silva Link: https://lore.kernel.org/r/20200227184808.GA1925@embeddedor Signed-off-by: Greg Kroah-Hartman --- drivers/char/mspec.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/char/mspec.c b/drivers/char/mspec.c index a9d9f074fbd6..7d583222e8fa 100644 --- a/drivers/char/mspec.c +++ b/drivers/char/mspec.c @@ -75,7 +75,7 @@ struct vma_data { enum mspec_page_type type; /* Type of pages allocated. */ unsigned long vm_start; /* Original (unsplit) base. */ unsigned long vm_end; /* Original (unsplit) end. */ - unsigned long maddr[0]; /* Array of MSPEC addresses. */ + unsigned long maddr[]; /* Array of MSPEC addresses. */ }; /*