* [PATCH] thermal: qcom: tsens.h: Replace zero-length array with flexible-array member
@ 2020-03-19 18:48 Gustavo A. R. Silva
2020-03-19 19:56 ` Amit Kucheria
2020-03-19 20:43 ` Daniel Lezcano
0 siblings, 2 replies; 3+ messages in thread
From: Gustavo A. R. Silva @ 2020-03-19 18:48 UTC (permalink / raw)
To: Andy Gross, Bjorn Andersson, Amit Kucheria, Zhang Rui, Daniel Lezcano
Cc: linux-arm-msm, linux-pm, 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/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);
--
2.23.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] thermal: qcom: tsens.h: Replace zero-length array with flexible-array member
2020-03-19 18:48 [PATCH] thermal: qcom: tsens.h: Replace zero-length array with flexible-array member Gustavo A. R. Silva
@ 2020-03-19 19:56 ` Amit Kucheria
2020-03-19 20:43 ` Daniel Lezcano
1 sibling, 0 replies; 3+ messages in thread
From: Amit Kucheria @ 2020-03-19 19:56 UTC (permalink / raw)
To: Gustavo A. R. Silva
Cc: Andy Gross, Bjorn Andersson, Zhang Rui, Daniel Lezcano,
linux-arm-msm, Linux PM list, LKML
On Fri, Mar 20, 2020 at 12:18 AM Gustavo A. R. Silva
<gustavo@embeddedor.com> 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>
Reviewed-by: Amit Kucheria <amit.kucheria@linaro.org>
> ---
> 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);
> --
> 2.23.0
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] thermal: qcom: tsens.h: Replace zero-length array with flexible-array member
2020-03-19 18:48 [PATCH] thermal: qcom: tsens.h: Replace zero-length array with flexible-array member Gustavo A. R. Silva
2020-03-19 19:56 ` Amit Kucheria
@ 2020-03-19 20:43 ` Daniel Lezcano
1 sibling, 0 replies; 3+ messages in thread
From: Daniel Lezcano @ 2020-03-19 20:43 UTC (permalink / raw)
To: Gustavo A. R. Silva, Andy Gross, Bjorn Andersson, Amit Kucheria,
Zhang Rui
Cc: linux-arm-msm, linux-pm, linux-kernel
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);
>
--
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2020-03-19 18:48 [PATCH] thermal: qcom: tsens.h: Replace zero-length array with flexible-array member Gustavo A. R. Silva
2020-03-19 19:56 ` Amit Kucheria
2020-03-19 20:43 ` Daniel Lezcano
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