[PATCH][next] toshiba: Replace zero-length array with flexible-array member

[PATCH][next] toshiba: Replace zero-length array with flexible-array member

[Gustavo A. R. Silva]

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/net/ethernet/toshiba/ps3_gelic_net.h      | 2 +-
 drivers/net/ethernet/toshiba/ps3_gelic_wireless.h | 2 +-
 drivers/net/ethernet/toshiba/spider_net.h         | 2 +-
 drivers/net/ethernet/toshiba/tc35815.c            | 2 +-
 4 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/toshiba/ps3_gelic_net.h b/drivers/net/ethernet/toshiba/ps3_gelic_net.h
index 805903dbddcc..68f324ed4eaf 100644
--- a/drivers/net/ethernet/toshiba/ps3_gelic_net.h
+++ b/drivers/net/ethernet/toshiba/ps3_gelic_net.h
@@ -308,7 +308,7 @@ struct gelic_port {
 	struct gelic_card *card;
 	struct net_device *netdev;
 	enum gelic_port_type type;
-	long priv[0]; /* long for alignment */
+	long priv[]; /* long for alignment */
 };
 
 static inline struct gelic_card *port_to_card(struct gelic_port *p)
diff --git a/drivers/net/ethernet/toshiba/ps3_gelic_wireless.h b/drivers/net/ethernet/toshiba/ps3_gelic_wireless.h
index 4041d946b649..1f203d1ae8db 100644
--- a/drivers/net/ethernet/toshiba/ps3_gelic_wireless.h
+++ b/drivers/net/ethernet/toshiba/ps3_gelic_wireless.h
@@ -158,7 +158,7 @@ struct gelic_eurus_scan_info {
 	__be32 reserved2;
 	__be32 reserved3;
 	__be32 reserved4;
-	u8 elements[0]; /* ie */
+	u8 elements[]; /* ie */
 } __packed;
 
 /* the hypervisor returns bbs up to 16 */
diff --git a/drivers/net/ethernet/toshiba/spider_net.h b/drivers/net/ethernet/toshiba/spider_net.h
index c0c68cbc898c..05b1a0736835 100644
--- a/drivers/net/ethernet/toshiba/spider_net.h
+++ b/drivers/net/ethernet/toshiba/spider_net.h
@@ -470,7 +470,7 @@ struct spider_net_card {
 	struct spider_net_extra_stats spider_stats;
 
 	/* Must be last item in struct */
-	struct spider_net_descr darray[0];
+	struct spider_net_descr darray[];
 };
 
 #endif
diff --git a/drivers/net/ethernet/toshiba/tc35815.c b/drivers/net/ethernet/toshiba/tc35815.c
index 3fd43d30b20d..b50c3ec3495b 100644
--- a/drivers/net/ethernet/toshiba/tc35815.c
+++ b/drivers/net/ethernet/toshiba/tc35815.c
@@ -367,7 +367,7 @@ struct TxFD {
 
 struct RxFD {
 	struct FDesc fd;
-	struct BDesc bd[0];	/* variable length */
+	struct BDesc bd[];	/* variable length */
 };
 
 struct FrFD {
-- 
2.25.0

Re: [PATCH][next] toshiba: Replace zero-length array with flexible-array member

[David Miller]

From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Date: Mon, 24 Feb 2020 10:32:52 -0600

> 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>

Applied.

Re: [PATCH][next] toshiba: Replace zero-length array with flexible-array member

[Geoff Levand]

On 2/24/20 8:32 AM, 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:

Seems fine.

Acked-by: Geoff Levand <geoff@infradead.org>