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* [PATCH] Input: gpio_keys - replace zero-length array with flexible-array member
@ 2020-02-13  0:26 Gustavo A. R. Silva
  2020-02-14  0:57 ` Dmitry Torokhov
  0 siblings, 1 reply; 2+ messages in thread
From: Gustavo A. R. Silva @ 2020-02-13  0:26 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/gpio_keys.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/input/keyboard/gpio_keys.c b/drivers/input/keyboard/gpio_keys.c
index 1f56d53454b2..53c9ff338dea 100644
--- a/drivers/input/keyboard/gpio_keys.c
+++ b/drivers/input/keyboard/gpio_keys.c
@@ -55,7 +55,7 @@ struct gpio_keys_drvdata {
 	struct input_dev *input;
 	struct mutex disable_lock;
 	unsigned short *keymap;
-	struct gpio_button_data data[0];
+	struct gpio_button_data data[];
 };
 
 /*
-- 
2.23.0


^ permalink raw reply	[flat|nested] 2+ messages in thread

* Re: [PATCH] Input: gpio_keys - replace zero-length array with flexible-array member
  2020-02-13  0:26 [PATCH] Input: gpio_keys - replace zero-length array with flexible-array member Gustavo A. R. Silva
@ 2020-02-14  0:57 ` Dmitry Torokhov
  0 siblings, 0 replies; 2+ messages in thread
From: Dmitry Torokhov @ 2020-02-14  0:57 UTC (permalink / raw)
  To: Gustavo A. R. Silva; +Cc: linux-input, linux-kernel

On Wed, Feb 12, 2020 at 06:26:00PM -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.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/input/keyboard/gpio_keys.c b/drivers/input/keyboard/gpio_keys.c
> index 1f56d53454b2..53c9ff338dea 100644
> --- a/drivers/input/keyboard/gpio_keys.c
> +++ b/drivers/input/keyboard/gpio_keys.c
> @@ -55,7 +55,7 @@ struct gpio_keys_drvdata {
>  	struct input_dev *input;
>  	struct mutex disable_lock;
>  	unsigned short *keymap;
> -	struct gpio_button_data data[0];
> +	struct gpio_button_data data[];
>  };
>  
>  /*
> -- 
> 2.23.0
> 

-- 
Dmitry

^ permalink raw reply	[flat|nested] 2+ messages in thread

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2020-02-13  0:26 [PATCH] Input: gpio_keys - replace zero-length array with flexible-array member Gustavo A. R. Silva
2020-02-14  0:57 ` Dmitry Torokhov

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