linux-kernel - [PATCH] USB: atm: Replace zero-length array with flexible-array member

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Message-ID: <20200211232148.GA20644@embeddedor>
Date:   Tue, 11 Feb 2020 17:21:48 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Matthieu CASTET <castet.matthieu@...e.fr>,
        Stanislaw Gruszka <stf_xl@...pl>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: [PATCH] USB: atm: Replace zero-length array with flexible-array
 member

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
inadvertenly introduced[3] to the codebase from now on.

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@...eddedor.com>
---
 drivers/usb/atm/ueagle-atm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/atm/ueagle-atm.c b/drivers/usb/atm/ueagle-atm.c
index 2754b4ce7136..25cf94131987 100644
--- a/drivers/usb/atm/ueagle-atm.c
+++ b/drivers/usb/atm/ueagle-atm.c
@@ -394,7 +394,7 @@ struct l1_code {
 	u8 string_header[E4_L1_STRING_HEADER];
 	u8 page_number_to_block_index[E4_MAX_PAGE_NUMBER];
 	struct block_index page_header[E4_NO_SWAPPAGE_HEADERS];
-	u8 code[0];
+	u8 code[];
 } __packed;
 
 /* structures describing a block within a DSP page */
-- 
2.25.0