| Message ID | 20200214171907.GA26588@embeddedor (mailing list archive) |
|---|---|
| State | Mainlined |
| Commit | 3d87c75d84e20d8812dbfba87e46ffca29d75d40 |
| Headers | show |
| Series | Input: gpio_keys_polled - replace zero-length array with flexible-array member | expand |
On Fri, Feb 14, 2020 at 11:19:07AM -0600, 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> Applied, thank you. > --- > drivers/input/keyboard/gpio_keys_polled.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/input/keyboard/gpio_keys_polled.c b/drivers/input/keyboard/gpio_keys_polled.c > index 6eb0a2f3f9de..c3937d2fc744 100644 > --- a/drivers/input/keyboard/gpio_keys_polled.c > +++ b/drivers/input/keyboard/gpio_keys_polled.c > @@ -38,7 +38,7 @@ struct gpio_keys_polled_dev { > const struct gpio_keys_platform_data *pdata; > unsigned long rel_axis_seen[BITS_TO_LONGS(REL_CNT)]; > unsigned long abs_axis_seen[BITS_TO_LONGS(ABS_CNT)]; > - struct gpio_keys_button_data data[0]; > + struct gpio_keys_button_data data[]; > }; > > static void gpio_keys_button_event(struct input_dev *input, > -- > 2.25.0 >
diff --git a/drivers/input/keyboard/gpio_keys_polled.c b/drivers/input/keyboard/gpio_keys_polled.c index 6eb0a2f3f9de..c3937d2fc744 100644 --- a/drivers/input/keyboard/gpio_keys_polled.c +++ b/drivers/input/keyboard/gpio_keys_polled.c @@ -38,7 +38,7 @@ struct gpio_keys_polled_dev { const struct gpio_keys_platform_data *pdata; unsigned long rel_axis_seen[BITS_TO_LONGS(REL_CNT)]; unsigned long abs_axis_seen[BITS_TO_LONGS(ABS_CNT)]; - struct gpio_keys_button_data data[0]; + struct gpio_keys_button_data data[]; }; static void gpio_keys_button_event(struct input_dev *input,
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/input/keyboard/gpio_keys_polled.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)