On 2/11/20 16:15, Alex Elder wrote:
On 2/11/20 3:12 PM, 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 inadvertenly introduced[3] to the codebase from now on.
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/staging/greybus/raw.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/staging/greybus/raw.c b/drivers/staging/greybus/raw.c index 838acbe84ca0..2b301b2aa107 100644 --- a/drivers/staging/greybus/raw.c +++ b/drivers/staging/greybus/raw.c @@ -30,7 +30,7 @@ struct gb_raw { struct raw_data { struct list_head entry; u32 len;
- u8 data[0];
- u8 data[];
}; static struct class *raw_class;
Does the kamlloc() call in receive_data() have any problems with the sizeof(*raw_data) passed as its argument?
Not in this case. It'd be different with a one-element array (u8 data[1]), though.
I'm not entirely sure what sizeof(struct-with-flexible-array-member) produces.
The same as sizeof(struct-with-zero-length-array):
"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]
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
-- Gustavo