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

[PATCH][next] libertas: 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/wireless/marvell/libertas/host.h    | 4 ++--
 drivers/net/wireless/marvell/libertas/if_sdio.c | 2 +-
 drivers/net/wireless/marvell/libertas/if_spi.c  | 2 +-
 drivers/net/wireless/marvell/libertas/if_usb.h  | 2 +-
 4 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/net/wireless/marvell/libertas/host.h b/drivers/net/wireless/marvell/libertas/host.h
index a4fc3f79bb17..dfa22468b14a 100644
--- a/drivers/net/wireless/marvell/libertas/host.h
+++ b/drivers/net/wireless/marvell/libertas/host.h
@@ -461,7 +461,7 @@ struct cmd_ds_802_11_scan {
 
 	uint8_t bsstype;
 	uint8_t bssid[ETH_ALEN];
-	uint8_t tlvbuffer[0];
+	uint8_t tlvbuffer[];
 } __packed;
 
 struct cmd_ds_802_11_scan_rsp {
@@ -469,7 +469,7 @@ struct cmd_ds_802_11_scan_rsp {
 
 	__le16 bssdescriptsize;
 	uint8_t nr_sets;
-	uint8_t bssdesc_and_tlvbuffer[0];
+	uint8_t bssdesc_and_tlvbuffer[];
 } __packed;
 
 struct cmd_ds_802_11_get_log {
diff --git a/drivers/net/wireless/marvell/libertas/if_sdio.c b/drivers/net/wireless/marvell/libertas/if_sdio.c
index 30f1025ecb9b..acf61b93b782 100644
--- a/drivers/net/wireless/marvell/libertas/if_sdio.c
+++ b/drivers/net/wireless/marvell/libertas/if_sdio.c
@@ -103,7 +103,7 @@ MODULE_FIRMWARE("sd8688.bin");
 struct if_sdio_packet {
 	struct if_sdio_packet	*next;
 	u16			nb;
-	u8			buffer[0] __attribute__((aligned(4)));
+	u8			buffer[] __aligned(4);
 };
 
 struct if_sdio_card {
diff --git a/drivers/net/wireless/marvell/libertas/if_spi.c b/drivers/net/wireless/marvell/libertas/if_spi.c
index d07fe82c557e..3625baa66d3e 100644
--- a/drivers/net/wireless/marvell/libertas/if_spi.c
+++ b/drivers/net/wireless/marvell/libertas/if_spi.c
@@ -35,7 +35,7 @@
 struct if_spi_packet {
 	struct list_head		list;
 	u16				blen;
-	u8				buffer[0] __attribute__((aligned(4)));
+	u8				buffer[] __aligned(4);
 };
 
 struct if_spi_card {
diff --git a/drivers/net/wireless/marvell/libertas/if_usb.h b/drivers/net/wireless/marvell/libertas/if_usb.h
index 8dc14bec3e16..7d0daeb33c3f 100644
--- a/drivers/net/wireless/marvell/libertas/if_usb.h
+++ b/drivers/net/wireless/marvell/libertas/if_usb.h
@@ -91,7 +91,7 @@ struct fwheader {
 struct fwdata {
 	struct fwheader hdr;
 	__le32 seqnum;
-	uint8_t data[0];
+	uint8_t data[];
 };
 
 /* fwsyncheader */
-- 
2.25.0

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

[Kalle Valo]

"Gustavo A. R. Silva" <gustavo@embeddedor.com> 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>

Patch applied to wireless-drivers-next.git, thanks.

c5047d5b831b libertas: Replace zero-length array with flexible-array member

-- 
https://patchwork.kernel.org/patch/11402377/

https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches