| Message ID | 20200319213839.GA10669@embeddedor.com (mailing list archive) |
|---|---|
| State | Mainlined |
| Commit | ef17f5193edd42e8913c93d0b601c101c56a15bb |
| Headers | show |
| Series | [next] hwspinlock: hwspinlock_internal.h: Replace zero-length array with flexible-array member | expand |
On Fri, Mar 20, 2020 at 5:38 AM Gustavo A. R. Silva <gustavo@embeddedor.com> 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> Looks good to me. Thanks. Reviewed-by: Baolin Wang <baolin.wang7@gmail.com> > --- > drivers/hwspinlock/hwspinlock_internal.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/hwspinlock/hwspinlock_internal.h b/drivers/hwspinlock/hwspinlock_internal.h > index 9eb6bd020dc7..29892767bb7a 100644 > --- a/drivers/hwspinlock/hwspinlock_internal.h > +++ b/drivers/hwspinlock/hwspinlock_internal.h > @@ -56,7 +56,7 @@ struct hwspinlock_device { > const struct hwspinlock_ops *ops; > int base_id; > int num_locks; > - struct hwspinlock lock[0]; > + struct hwspinlock lock[]; > }; > > static inline int hwlock_to_id(struct hwspinlock *hwlock) > -- > 2.23.0 >
diff --git a/drivers/hwspinlock/hwspinlock_internal.h b/drivers/hwspinlock/hwspinlock_internal.h index 9eb6bd020dc7..29892767bb7a 100644 --- a/drivers/hwspinlock/hwspinlock_internal.h +++ b/drivers/hwspinlock/hwspinlock_internal.h @@ -56,7 +56,7 @@ struct hwspinlock_device { const struct hwspinlock_ops *ops; int base_id; int num_locks; - struct hwspinlock lock[0]; + struct hwspinlock lock[]; }; static inline int hwlock_to_id(struct hwspinlock *hwlock)
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> --- drivers/hwspinlock/hwspinlock_internal.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)