* [PATCH] Input: tca6416-keypad - replace zero-length array with flexible-array member
@ 2020-02-14 17:20 Gustavo A. R. Silva
2020-02-15 23:30 ` Dmitry Torokhov
0 siblings, 1 reply; 2+ messages in thread
From: Gustavo A. R. Silva @ 2020-02-14 17:20 UTC (permalink / raw)
To: Dmitry Torokhov; +Cc: linux-input, linux-kernel, Gustavo A. R. Silva
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/tca6416-keypad.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/input/keyboard/tca6416-keypad.c b/drivers/input/keyboard/tca6416-keypad.c
index 2a14769de637..21758767ccf0 100644
--- a/drivers/input/keyboard/tca6416-keypad.c
+++ b/drivers/input/keyboard/tca6416-keypad.c
@@ -33,7 +33,7 @@ MODULE_DEVICE_TABLE(i2c, tca6416_id);
struct tca6416_drv_data {
struct input_dev *input;
- struct tca6416_button data[0];
+ struct tca6416_button data[];
};
struct tca6416_keypad_chip {
@@ -48,7 +48,7 @@ struct tca6416_keypad_chip {
int irqnum;
u16 pinmask;
bool use_polling;
- struct tca6416_button buttons[0];
+ struct tca6416_button buttons[];
};
static int tca6416_write_reg(struct tca6416_keypad_chip *chip, int reg, u16 val)
--
2.25.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] Input: tca6416-keypad - replace zero-length array with flexible-array member
2020-02-14 17:20 [PATCH] Input: tca6416-keypad - replace zero-length array with flexible-array member Gustavo A. R. Silva
@ 2020-02-15 23:30 ` Dmitry Torokhov
0 siblings, 0 replies; 2+ messages in thread
From: Dmitry Torokhov @ 2020-02-15 23:30 UTC (permalink / raw)
To: Gustavo A. R. Silva; +Cc: linux-input, linux-kernel
On Fri, Feb 14, 2020 at 11:20:22AM -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/tca6416-keypad.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/input/keyboard/tca6416-keypad.c b/drivers/input/keyboard/tca6416-keypad.c
> index 2a14769de637..21758767ccf0 100644
> --- a/drivers/input/keyboard/tca6416-keypad.c
> +++ b/drivers/input/keyboard/tca6416-keypad.c
> @@ -33,7 +33,7 @@ MODULE_DEVICE_TABLE(i2c, tca6416_id);
>
> struct tca6416_drv_data {
> struct input_dev *input;
> - struct tca6416_button data[0];
> + struct tca6416_button data[];
> };
>
> struct tca6416_keypad_chip {
> @@ -48,7 +48,7 @@ struct tca6416_keypad_chip {
> int irqnum;
> u16 pinmask;
> bool use_polling;
> - struct tca6416_button buttons[0];
> + struct tca6416_button buttons[];
> };
>
> static int tca6416_write_reg(struct tca6416_keypad_chip *chip, int reg, u16 val)
> --
> 2.25.0
>
--
Dmitry
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