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.
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/block/rsxx/dma.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/block/rsxx/dma.c b/drivers/block/rsxx/dma.c
index 111eb659e66d..1914f5488b22 100644
--- a/drivers/block/rsxx/dma.c
+++ b/drivers/block/rsxx/dma.c
@@ -80,7 +80,7 @@ struct dma_tracker {
struct dma_tracker_list {
spinlock_t lock;
int head;
- struct dma_tracker list[0];
+ struct dma_tracker list[];
};
--
2.25.0
Hi all,
Friendly ping: Who can take this?
Thanks
--
Gustavo
On 2/12/20 1:46 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.
>
> 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/block/rsxx/dma.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/block/rsxx/dma.c b/drivers/block/rsxx/dma.c
> index 111eb659e66d..1914f5488b22 100644
> --- a/drivers/block/rsxx/dma.c
> +++ b/drivers/block/rsxx/dma.c
> @@ -80,7 +80,7 @@ struct dma_tracker {
> struct dma_tracker_list {
> spinlock_t lock;
> int head;
> - struct dma_tracker list[0];
> + struct dma_tracker list[];
> };
>
>
>
On 2/12/20 12:46 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.
>
> 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")
Applied for 5.7, thanks.
--
Jens Axboe
On 3/19/20 4:27 PM, Jens Axboe wrote:
>>
>> [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")
>
> Applied for 5.7, thanks.
>
Thanks, Jens.
--
Gustavo