carl9170: 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 76497732932f ("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
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>

diff --git a/include/shared/fwcmd.h b/include/shared/fwcmd.h
index 2a58dd88b21ef39dae5d095ae21dc1211884ca29..4a500095555c67d9baea63c6ffe41e4839c13996 100644 (file)
--- a/include/shared/fwcmd.h
+++ b/include/shared/fwcmd.h
@@ -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

diff --git a/include/shared/hw.h b/include/shared/hw.h
index 08e0ae9c5836dc38d7d4f2d9f5abe71d8af86a66..555ad49759707130e4bf83c40de396cfcb102568 100644 (file)
--- a/include/shared/hw.h
+++ b/include/shared/hw.h
@@ -851,7 +851,7 @@ struct ar9170_stream {
        __le16 length;
        __le16 tag;
 
-       u8 payload[0];
+       u8 payload[];
 } __packed __aligned(4);
 #define AR9170_STREAM_LEN                              4