* [PATCH] wcn36xx: Replace zero-length array with flexible-array
@ 2020-05-07 15:17 Gustavo A. R. Silva
2020-05-13 16:03 ` Kalle Valo
0 siblings, 1 reply; 2+ messages in thread
From: Gustavo A. R. Silva @ 2020-05-07 15:17 UTC (permalink / raw)
To: Kalle Valo, David S. Miller, Maxime Coquelin, Alexandre Torgue
Cc: wcn36xx, linux-wireless, netdev, linux-kernel, linux-stm32,
linux-arm-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]
sizeof(flexible-array-member) triggers a warning because flexible array
members have incomplete type[1]. There are some instances of code in
which the sizeof operator is being incorrectly/erroneously applied to
zero-length arrays and the result is zero. Such instances may be hiding
some bugs. So, this work (flexible-array member conversions) will also
help to get completely rid of those sorts of issues.
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 <gustavoars@kernel.org>
---
drivers/net/wireless/ath/wcn36xx/hal.h | 4 ++--
drivers/net/wireless/ath/wcn36xx/testmode.h | 2 +-
2 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/net/wireless/ath/wcn36xx/hal.h b/drivers/net/wireless/ath/wcn36xx/hal.h
index 6ba0fd57c951..aab5a58616fc 100644
--- a/drivers/net/wireless/ath/wcn36xx/hal.h
+++ b/drivers/net/wireless/ath/wcn36xx/hal.h
@@ -2240,7 +2240,7 @@ struct wcn36xx_hal_process_ptt_msg_req_msg {
struct wcn36xx_hal_msg_header header;
/* Actual FTM Command body */
- u8 ptt_msg[0];
+ u8 ptt_msg[];
} __packed;
struct wcn36xx_hal_process_ptt_msg_rsp_msg {
@@ -2249,7 +2249,7 @@ struct wcn36xx_hal_process_ptt_msg_rsp_msg {
/* FTM Command response status */
u32 ptt_msg_resp_status;
/* Actual FTM Command body */
- u8 ptt_msg[0];
+ u8 ptt_msg[];
} __packed;
struct update_edca_params_req_msg {
diff --git a/drivers/net/wireless/ath/wcn36xx/testmode.h b/drivers/net/wireless/ath/wcn36xx/testmode.h
index 4c6cfdb46580..09d68fab9add 100644
--- a/drivers/net/wireless/ath/wcn36xx/testmode.h
+++ b/drivers/net/wireless/ath/wcn36xx/testmode.h
@@ -20,7 +20,7 @@ struct ftm_rsp_msg {
u16 msg_id;
u16 msg_body_length;
u32 resp_status;
- u8 msg_response[0];
+ u8 msg_response[];
} __packed;
/* The request buffer of FTM which contains a byte of command and the request */
--
2.26.2
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] wcn36xx: Replace zero-length array with flexible-array
2020-05-07 15:17 [PATCH] wcn36xx: Replace zero-length array with flexible-array Gustavo A. R. Silva
@ 2020-05-13 16:03 ` Kalle Valo
0 siblings, 0 replies; 2+ messages in thread
From: Kalle Valo @ 2020-05-13 16:03 UTC (permalink / raw)
To: Gustavo A. R. Silva
Cc: David S. Miller, Maxime Coquelin, Alexandre Torgue, wcn36xx,
linux-wireless, netdev, linux-kernel, linux-stm32,
linux-arm-kernel, Gustavo A. R. Silva
"Gustavo A. R. Silva" <gustavoars@kernel.org> 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]
>
> sizeof(flexible-array-member) triggers a warning because flexible array
> members have incomplete type[1]. There are some instances of code in
> which the sizeof operator is being incorrectly/erroneously applied to
> zero-length arrays and the result is zero. Such instances may be hiding
> some bugs. So, this work (flexible-array member conversions) will also
> help to get completely rid of those sorts of issues.
>
> 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 <gustavoars@kernel.org>
> Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Patch applied to ath-next branch of ath.git, thanks.
ec431188b419 wcn36xx: Replace zero-length array with flexible-array
--
https://patchwork.kernel.org/patch/11534309/
https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches
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