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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 7649773293 ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Gustavo A. R. Silva 2020-02-26 15:23:17 -06:00 committed by David S. Miller
parent da60fbe7ef
commit 37e1244a79
2 changed files with 2 additions and 2 deletions
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2
drivers/net/wan/farsync.h
View File

@ -65,7 +65,7 @@
struct fstioc_write { struct fstioc_write {
unsigned int size; unsigned int size;
unsigned int offset; unsigned int offset;
unsigned char data[0]; unsigned char data[];
}; };

2
drivers/net/wan/wanxl.c
View File

@ -78,7 +78,7 @@ struct card {
struct sk_buff *rx_skbs[RX_QUEUE_LENGTH]; struct sk_buff *rx_skbs[RX_QUEUE_LENGTH];
struct card_status *status; /* shared between host and card */ struct card_status *status; /* shared between host and card */
dma_addr_t status_address; dma_addr_t status_address;
struct port ports[0]; /* 1 - 4 port structures follow */ struct port ports[]; /* 1 - 4 port structures follow */
}; };