WAN: Replace zero-length array with flexible-array member

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>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/wan/farsync.h b/drivers/net/wan/farsync.h
index 47b8e36f97ab79637abf27625b88c2a9f08266f4..5f43568a971577c55fcd7d0ab25d5435e23a0647 100644 (file)
--- a/drivers/net/wan/farsync.h
+++ b/drivers/net/wan/farsync.h
@@ -65,7 +65,7 @@
 struct fstioc_write {
         unsigned int  size;
         unsigned int  offset;
-        unsigned char data[0];
+       unsigned char data[];
 };
 
 

diff --git a/drivers/net/wan/wanxl.c b/drivers/net/wan/wanxl.c
index 23f93f1c815d0914d3936cfebf2d7c542fc095bd..499f7cd19a4a870eb2b1ccdc662a398a46a0763e 100644 (file)
--- a/drivers/net/wan/wanxl.c
+++ b/drivers/net/wan/wanxl.c
@@ -78,7 +78,7 @@ struct card {
        struct sk_buff *rx_skbs[RX_QUEUE_LENGTH];
        struct card_status *status;     /* shared between host and card */
        dma_addr_t status_address;
-       struct port ports[0];   /* 1 - 4 port structures follow */
+       struct port ports[];    /* 1 - 4 port structures follow */
 };