* [PATCH][next] media: venus: hfi_cmds.h: Replace zero-length array with flexible-array member
@ 2020-03-19 22:21 Gustavo A. R. Silva
2020-04-01 8:37 ` Stanimir Varbanov
0 siblings, 1 reply; 2+ messages in thread
From: Gustavo A. R. Silva @ 2020-03-19 22:21 UTC (permalink / raw)
To: Stanimir Varbanov, Andy Gross, Bjorn Andersson, Mauro Carvalho Chehab
Cc: linux-media, linux-arm-msm, 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/media/platform/qcom/venus/hfi_cmds.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/media/platform/qcom/venus/hfi_cmds.h b/drivers/media/platform/qcom/venus/hfi_cmds.h
index cae9d5d61c0c..83705e237f1c 100644
--- a/drivers/media/platform/qcom/venus/hfi_cmds.h
+++ b/drivers/media/platform/qcom/venus/hfi_cmds.h
@@ -107,7 +107,7 @@ struct hfi_session_abort_pkt {
struct hfi_session_set_property_pkt {
struct hfi_session_hdr_pkt shdr;
u32 num_properties;
- u32 data[0];
+ u32 data[];
};
struct hfi_session_set_buffers_pkt {
--
2.23.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH][next] media: venus: hfi_cmds.h: Replace zero-length array with flexible-array member
2020-03-19 22:21 [PATCH][next] media: venus: hfi_cmds.h: Replace zero-length array with flexible-array member Gustavo A. R. Silva
@ 2020-04-01 8:37 ` Stanimir Varbanov
0 siblings, 0 replies; 2+ messages in thread
From: Stanimir Varbanov @ 2020-04-01 8:37 UTC (permalink / raw)
To: Gustavo A. R. Silva, Stanimir Varbanov, Andy Gross,
Bjorn Andersson, Mauro Carvalho Chehab
Cc: linux-media, linux-arm-msm, linux-kernel
Hi Gustavo,
Thanks for the patch!
On 3/20/20 12:21 AM, 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/media/platform/qcom/venus/hfi_cmds.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
Acked-by: Stanimir Varbanov <staninmir.varbanov@linaro.org>
> diff --git a/drivers/media/platform/qcom/venus/hfi_cmds.h b/drivers/media/platform/qcom/venus/hfi_cmds.h
> index cae9d5d61c0c..83705e237f1c 100644
> --- a/drivers/media/platform/qcom/venus/hfi_cmds.h
> +++ b/drivers/media/platform/qcom/venus/hfi_cmds.h
> @@ -107,7 +107,7 @@ struct hfi_session_abort_pkt {
> struct hfi_session_set_property_pkt {
> struct hfi_session_hdr_pkt shdr;
> u32 num_properties;
> - u32 data[0];
> + u32 data[];
> };
>
> struct hfi_session_set_buffers_pkt {
>
--
regards,
Stan
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2020-04-01 8:37 ` Stanimir Varbanov
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