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 <[email protected]>
---
drivers/platform/chrome/wilco_ec/event.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/platform/chrome/wilco_ec/event.c b/drivers/platform/chrome/wilco_ec/event.c
index dba3d445623f..814518509739 100644
--- a/drivers/platform/chrome/wilco_ec/event.c
+++ b/drivers/platform/chrome/wilco_ec/event.c
@@ -79,7 +79,7 @@ static DEFINE_IDA(event_ida);
struct ec_event {
u16 size;
u16 type;
- u16 event[0];
+ u16 event[];
} __packed;
#define ec_event_num_words(ev) (ev->size - 1)
@@ -96,7 +96,7 @@ struct ec_event_queue {
int capacity;
int head;
int tail;
- struct ec_event *entries[0];
+ struct ec_event *entries[];
};
/* Maximum number of events to store in ec_event_queue */
--
2.23.0
Hi Gustavo
On 21/3/20 0:16, 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 <[email protected]>
Queued for 5.7. Thanks!
~ Enric
> ---
> drivers/platform/chrome/wilco_ec/event.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/platform/chrome/wilco_ec/event.c b/drivers/platform/chrome/wilco_ec/event.c
> index dba3d445623f..814518509739 100644
> --- a/drivers/platform/chrome/wilco_ec/event.c
> +++ b/drivers/platform/chrome/wilco_ec/event.c
> @@ -79,7 +79,7 @@ static DEFINE_IDA(event_ida);
> struct ec_event {
> u16 size;
> u16 type;
> - u16 event[0];
> + u16 event[];
> } __packed;
>
> #define ec_event_num_words(ev) (ev->size - 1)
> @@ -96,7 +96,7 @@ struct ec_event_queue {
> int capacity;
> int head;
> int tail;
> - struct ec_event *entries[0];
> + struct ec_event *entries[];
> };
>
> /* Maximum number of events to store in ec_event_queue */
>