| Message ID | 20200228135959.GA30464@embeddedor (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
| Series | [next] cfg802154: Replace zero-length array with flexible-array member | expand |
Hello. On 28.02.20 14:59, Gustavo A. R. Silva wrote: > 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/net/cfg802154.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/net/cfg802154.h b/include/net/cfg802154.h > index 6f86073a5d7d..6ed07844eb24 100644 > --- a/include/net/cfg802154.h > +++ b/include/net/cfg802154.h > @@ -214,7 +214,7 @@ struct wpan_phy { > /* the network namespace this phy lives in currently */ > possible_net_t _net; > > - char priv[0] __aligned(NETDEV_ALIGN); > + char priv[] __aligned(NETDEV_ALIGN); > }; > > static inline struct net *wpan_phy_net(struct wpan_phy *wpan_phy) > This patch has been applied to the wpan-next tree and will be part of the next pull request to net-next. Thanks! regards Stefan Schmidt
diff --git a/include/net/cfg802154.h b/include/net/cfg802154.h index 6f86073a5d7d..6ed07844eb24 100644 --- a/include/net/cfg802154.h +++ b/include/net/cfg802154.h @@ -214,7 +214,7 @@ struct wpan_phy { /* the network namespace this phy lives in currently */ possible_net_t _net; - char priv[0] __aligned(NETDEV_ALIGN); + char priv[] __aligned(NETDEV_ALIGN); }; static inline struct net *wpan_phy_net(struct wpan_phy *wpan_phy)
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/net/cfg802154.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)