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wcn36xx: Replace zero-length array with flexible-array 

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 7649773293 ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200507151758.GA4962@embeddedor
This commit is contained in:
Gustavo A. R. Silva 2020-05-07 10:17:58 -05:00 committed by Kalle Valo
parent 012f814568
commit ec431188b4
2 changed files with 3 additions and 3 deletions
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4
drivers/net/wireless/ath/wcn36xx/hal.h
View File

@ -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 {

2
drivers/net/wireless/ath/wcn36xx/testmode.h
View File

@ -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 */