| Message ID | 20200507192652.GA16743@embeddedor |
|---|---|
| State | Accepted |
| Headers | show |
| Series | um: virtio: Replace zero-length array with flexible-array | expand |
diff --git a/arch/um/drivers/vector_kern.h b/arch/um/drivers/vector_kern.h index d0159082faf0..8fff93a75a92 100644 --- a/arch/um/drivers/vector_kern.h +++ b/arch/um/drivers/vector_kern.h @@ -129,7 +129,7 @@ struct vector_private { struct vector_estats estats; struct sock_fprog *bpf; - char user[0]; + char user[]; }; extern int build_transport_data(struct vector_private *vp); diff --git a/arch/um/drivers/vhost_user.h b/arch/um/drivers/vhost_user.h index 6c71b6005177..6f147cd3c9f7 100644 --- a/arch/um/drivers/vhost_user.h +++ b/arch/um/drivers/vhost_user.h @@ -78,7 +78,7 @@ struct vhost_user_config { u32 offset; u32 size; u32 flags; - u8 payload[0]; /* Variable length */ + u8 payload[]; /* Variable length */ } __packed; struct vhost_user_vring_state {
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] sizeof(flexible-array-member) triggers a warning because flexible array members have incomplete type[1]. There are some instances of code in which the sizeof operator is being incorrectly/erroneously applied to zero-length arrays and the result is zero. Such instances may be hiding some bugs. So, this work (flexible-array member conversions) will also help to get completely rid of those sorts of issues. 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 <gustavoars@kernel.org> --- arch/um/drivers/vector_kern.h | 2 +- arch/um/drivers/vhost_user.h | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)