diff mbox series

thermal: qcom: tsens.h: Replace zero-length array with flexible-array member

Message ID 20200319184838.GA25767@embeddedor.com
State New
Headers show
Series thermal: qcom: tsens.h: Replace zero-length array with flexible-array member | expand

Commit Message

Gustavo A. R. Silva March 19, 2020, 6:48 p.m. UTC
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/thermal/qcom/tsens.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Daniel Lezcano March 19, 2020, 8:43 p.m. UTC | #1
On 19/03/2020 19:48, 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, thanks

> ---
>  drivers/thermal/qcom/tsens.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/thermal/qcom/tsens.h b/drivers/thermal/qcom/tsens.h
> index e24a865fbc34..92503712596a 100644
> --- a/drivers/thermal/qcom/tsens.h
> +++ b/drivers/thermal/qcom/tsens.h
> @@ -488,7 +488,7 @@ struct tsens_priv {
>  	struct dentry			*debug_root;
>  	struct dentry			*debug;
>  
> -	struct tsens_sensor		sensor[0];
> +	struct tsens_sensor		sensor[];
>  };
>  
>  char *qfprom_read(struct device *dev, const char *cname);
>
diff mbox series

Patch

diff --git a/drivers/thermal/qcom/tsens.h b/drivers/thermal/qcom/tsens.h
index e24a865fbc34..92503712596a 100644
--- a/drivers/thermal/qcom/tsens.h
+++ b/drivers/thermal/qcom/tsens.h
@@ -488,7 +488,7 @@  struct tsens_priv {
 	struct dentry			*debug_root;
 	struct dentry			*debug;
 
-	struct tsens_sensor		sensor[0];
+	struct tsens_sensor		sensor[];
 };
 
 char *qfprom_read(struct device *dev, const char *cname);