* [PATCH][next] fpga: dfl.h: Replace zero-length array with flexible-array member
@ 2020-03-19 21:21 Gustavo A. R. Silva
2020-03-21 20:10 ` Moritz Fischer
0 siblings, 1 reply; 2+ messages in thread
From: Gustavo A. R. Silva @ 2020-03-19 21:21 UTC (permalink / raw)
To: Wu Hao, Moritz Fischer; +Cc: linux-fpga, 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/fpga/dfl.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/fpga/dfl.h b/drivers/fpga/dfl.h
index 4a9a33cd9979..74784d3cfe7c 100644
--- a/drivers/fpga/dfl.h
+++ b/drivers/fpga/dfl.h
@@ -235,7 +235,7 @@ struct dfl_feature_platform_data {
int open_count;
void *private;
int num;
- struct dfl_feature features[0];
+ struct dfl_feature features[];
};
static inline
--
2.23.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH][next] fpga: dfl.h: Replace zero-length array with flexible-array member
2020-03-19 21:21 [PATCH][next] fpga: dfl.h: Replace zero-length array with flexible-array member Gustavo A. R. Silva
@ 2020-03-21 20:10 ` Moritz Fischer
0 siblings, 0 replies; 2+ messages in thread
From: Moritz Fischer @ 2020-03-21 20:10 UTC (permalink / raw)
To: Gustavo A. R. Silva; +Cc: Wu Hao, Moritz Fischer, linux-fpga, linux-kernel
On Thu, Mar 19, 2020 at 04:21:53PM -0500, 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>
> ---
> drivers/fpga/dfl.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/fpga/dfl.h b/drivers/fpga/dfl.h
> index 4a9a33cd9979..74784d3cfe7c 100644
> --- a/drivers/fpga/dfl.h
> +++ b/drivers/fpga/dfl.h
> @@ -235,7 +235,7 @@ struct dfl_feature_platform_data {
> int open_count;
> void *private;
> int num;
> - struct dfl_feature features[0];
> + struct dfl_feature features[];
> };
>
> static inline
> --
> 2.23.0
>
Applied to for-next,
Thanks
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