Hi,
On 2/20/20 13:04, Adham.Abozaeid@microchip.com wrote:
Hi Gustavo
On 2/20/20 6:29 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:
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
static void cfg_scan_result(enum scan_event scan_event, diff --git a/drivers/staging/wilc1000/spi.c b/drivers/staging/wilc1000/spi.c index 44f7d48851b5..11653ac118cd 100644 --- a/drivers/staging/wilc1000/spi.c +++ b/drivers/staging/wilc1000/spi.c @@ -139,7 +139,7 @@ struct wilc_spi_read_rsp_data { u8 status; u8 resp_header; u8 resp_data[4];
u8 crc[0];
u8 crc[];} __packed;
more zero-length arrays in wilc1000, spi.c, struct wilc_spi_cmd, and in fw.h
Oh wow, I hadn't thought about cases like this:
struct wilc_spi_cmd { u8 cmd_type; union { struct { u8 addr[3]; u8 crc[0]; } __packed simple_cmd; struct { u8 addr[3]; u8 size[2]; u8 crc[0]; } __packed dma_cmd; struct { u8 addr[3]; u8 size[3]; u8 crc[0]; } __packed dma_cmd_ext; struct { u8 addr[2]; __be32 data; u8 crc[0]; } __packed internal_w_cmd; struct { u8 addr[3]; __be32 data; u8 crc[0]; } __packed w_cmd; } u; } __packed;
Thanks for the feedback. -- Gustavo