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R. Silva" In-Reply-To: <20221116170526.752c304b@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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 - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - embeddedor.com X-BWhitelist: no X-Source-IP: 187.162.31.110 X-Source-L: No X-Exim-ID: 1ovTaS-001jBu-26 X-Source: X-Source-Args: X-Source-Dir: X-Source-Sender: 187-162-31-110.static.axtel.net ([192.168.15.7]) [187.162.31.110]:57016 X-Source-Auth: gustavo@embeddedor.com X-Email-Count: 0 X-Org: HG=hgshared;ORG=hostgator; X-Source-Cap: Z3V6aWRpbmU7Z3V6aWRpbmU7Z2F0b3I0MTY2Lmhvc3RnYXRvci5jb20= X-Local-Domain: yes X-CMAE-Envelope: MS4xfGnFtwXyMzEZr0qCQ2E57yecRpTyr4V7mLRrI/N5+fofzAMLl/3YJvDZkX+M+AlacciKVOB7Yp6hNA7rDmy8K2NluJ61jKu3FxM94N0qC9U5ROmWOtan Maak1/0HAGGTy6eGvb9J1UPBMB7N9DL5Qz+ICFmSqsBWBCccPeHD/eHbDwfCmIhPuTa29mBHZWy04lb4bouMM4Drya2v0sQnhrdxdB2cCbB96HkUk/WR8xSU cKRI8Pjm3fstyZYzTsTuMw== Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 11/16/22 19:05, Jakub Kicinski wrote: > On Wed, 16 Nov 2022 18:55:36 -0600 Gustavo A. R. Silva wrote: >>> @@ -56,7 +55,6 @@ struct nlmsghdr { >>> __u16 nlmsg_flags; >>> __u32 nlmsg_seq; >>> __u32 nlmsg_pid; >>> - __u8 nlmsg_data[]; >>> }; >> >> This seems to be a sensible change. In general, it's not a good idea >> to have variable length objects (flex-array members) in structures used >> as headers, and that we know will ultimately be followed by more objects >> when embedded inside other structures. > > Meaning we should go back to zero-length arrays instead? No. > Is there something in the standard that makes flexible array > at the end of an embedded struct a problem? I haven't seen any problems ss long as the flex-array appears last: struct foo { ... members struct boo { ... members char flex[]; }; }; struct complex { ... members struct foo embedded; }; However, the GCC docs[1] mention this: "A structure containing a flexible array member [..] may not be a member of a structure [..] (However, these uses are permitted by GCC as extensions.)" And in this case it seems that's the reason why GCC doesn't complain? -- Gustavo [1] https://gcc.gnu.org/onlinedocs/gcc-12.2.0/gcc/Zero-Length.html#Zero-Length