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R. Silva" To: Dan Williams , Vishal Verma , Dave Jiang , Ira Weiny Subject: [PATCH][next] nvdimm: label.h: Replace zero-length array with flexible-array member Message-ID: <20200319230737.GA16452@embeddedor.com> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.9.4 (2018-02-28) X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - gator4166.hostgator.com X-AntiAbuse: Original Domain - lists.01.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - embeddedor.com X-BWhitelist: no X-Source-IP: 189.218.116.241 X-Source-L: No X-Exim-ID: 1jF4GI-002PZ0-A4 X-Source: X-Source-Args: X-Source-Dir: X-Source-Sender: cablelink-189-218-116-241.hosts.intercable.net (embeddedor) [189.218.116.241]:54038 X-Source-Auth: gustavo@embeddedor.com X-Email-Count: 15 X-Source-Cap: Z3V6aWRpbmU7Z3V6aWRpbmU7Z2F0b3I0MTY2Lmhvc3RnYXRvci5jb20= X-Local-Domain: yes Message-ID-Hash: SBEJL6QZF3LRDNEQ2USPV4TWFGEJ34BX X-Message-ID-Hash: SBEJL6QZF3LRDNEQ2USPV4TWFGEJ34BX X-MailFrom: gustavo@embeddedor.com X-Mailman-Rule-Hits: nonmember-moderation X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation CC: linux-nvdimm@lists.01.org, linux-kernel@vger.kernel.org, "Gustavo A. R. Silva" X-Mailman-Version: 3.1.1 Precedence: list List-Id: "Linux-nvdimm developer list." Archived-At: List-Archive: List-Help: List-Post: List-Subscribe: List-Unsubscribe: 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 --- drivers/nvdimm/label.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/nvdimm/label.h b/drivers/nvdimm/label.h index 4c7b775c2811..956b6d1bd8cc 100644 --- a/drivers/nvdimm/label.h +++ b/drivers/nvdimm/label.h @@ -62,7 +62,7 @@ struct nd_namespace_index { __le16 major; __le16 minor; __le64 checksum; - u8 free[0]; + u8 free[]; }; /**