linux-kernel - [PATCH] staging: unisys: visorinput: Replace zero-length array with flexible-array member

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Message-ID: <20200211211722.GA1640@embeddedor>
Date:   Tue, 11 Feb 2020 15:17:22 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     David Kershner <david.kershner@...sys.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     sparmaintainer@...sys.com, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: [PATCH] staging: unisys: visorinput: 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/staging/unisys/visorinput/visorinput.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/staging/unisys/visorinput/visorinput.c b/drivers/staging/unisys/visorinput/visorinput.c
index 9693fb559052..6d202cba8575 100644
--- a/drivers/staging/unisys/visorinput/visorinput.c
+++ b/drivers/staging/unisys/visorinput/visorinput.c
@@ -111,7 +111,7 @@ struct visorinput_devdata {
 	/* size of following array */
 	unsigned int keycode_table_bytes;
 	/* for keyboard devices: visorkbd_keycode[] + visorkbd_ext_keycode[] */
-	unsigned char keycode_table[0];
+	unsigned char keycode_table[];
 };
 
 static const guid_t visor_keyboard_channel_guid = VISOR_KEYBOARD_CHANNEL_GUID;
-- 
2.25.0