| Message ID | 20200217200111.GA5283@embeddedor |
|---|---|
| State | Changes Requested |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | [next] bpf, sockmap: Replace zero-length array with flexible-array member | expand |
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> > --- > net/core/sock_map.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/net/core/sock_map.c b/net/core/sock_map.c > index 085cef5857bb..3a7a96ab088a 100644 > --- a/net/core/sock_map.c > +++ b/net/core/sock_map.c > @@ -518,7 +518,7 @@ struct bpf_htab_elem { > u32 hash; > struct sock *sk; > struct hlist_node node; > - u8 key[0]; > + u8 key[]; > }; > > struct bpf_htab_bucket { > -- > 2.25.0 > The same pattern is in ./kernel/bpf/hashtab.c can you also change it here then if this is the case so sockmap is aligned with bpf coding style. .John
diff --git a/net/core/sock_map.c b/net/core/sock_map.c index 085cef5857bb..3a7a96ab088a 100644 --- a/net/core/sock_map.c +++ b/net/core/sock_map.c @@ -518,7 +518,7 @@ struct bpf_htab_elem { u32 hash; struct sock *sk; struct hlist_node node; - u8 key[0]; + u8 key[]; }; struct bpf_htab_bucket {
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> --- net/core/sock_map.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)