Messages in this thread Patch in this message | | | Date | Mon, 2 Mar 2020 06:02:09 -0600 | From | "Gustavo A. R. Silva" <> | Subject | [PATCH][next] drop_monitor: Replace zero-length array with flexible-array member |
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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 <gustavo@embeddedor.com> --- include/uapi/linux/net_dropmon.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/include/uapi/linux/net_dropmon.h b/include/uapi/linux/net_dropmon.h index 66048cc5d7b3..67e31f329190 100644 --- a/include/uapi/linux/net_dropmon.h +++ b/include/uapi/linux/net_dropmon.h @@ -29,12 +29,12 @@ struct net_dm_config_entry { struct net_dm_config_msg { __u32 entries; - struct net_dm_config_entry options[0]; + struct net_dm_config_entry options[]; }; struct net_dm_alert_msg { __u32 entries; - struct net_dm_drop_point points[0]; + struct net_dm_drop_point points[]; }; struct net_dm_user_msg { -- 2.25.0
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