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carl9170: Replace zero-length array with flexible-array

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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/20200507151921.GA5083@embeddedor
This commit is contained in:
Gustavo A. R. Silva
2020-05-07 10:19:21 -05:00
committed by Kalle Valo
parent 4d0f3604c4
commit 103dc3dab2
2 changed files with 2 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/net/wireless/ath/carl9170/fwcmd.h
View File

@@ -127,7 +127,7 @@ struct carl9170_write_reg {
struct carl9170_write_reg_byte {
__le32 addr;
__le32 count;
u8 val[0];
u8 val[];
} __packed;
#define CARL9170FW_PHY_HT_ENABLE 0x4

2
drivers/net/wireless/ath/carl9170/hw.h
View File

@@ -851,7 +851,7 @@ struct ar9170_stream {
__le16 length;
__le16 tag;
u8 payload[0];
u8 payload[];
} __packed __aligned(4);
#define AR9170_STREAM_LEN 4