linux-kernel - [PATCH] USB: serial: ti_usb_3410_5052: Replace zero-length array with flexible-array member

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Message-ID: <20200211232420.GA22388@embeddedor>
Date:   Tue, 11 Feb 2020 17:24:20 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Johan Hovold <johan@...nel.org>,
        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: serial: ti_usb_3410_5052: 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/serial/ti_usb_3410_5052.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/serial/ti_usb_3410_5052.c b/drivers/usb/serial/ti_usb_3410_5052.c
index dd0ad67aa71e..db3ab25d9228 100644
--- a/drivers/usb/serial/ti_usb_3410_5052.c
+++ b/drivers/usb/serial/ti_usb_3410_5052.c
@@ -219,7 +219,7 @@ struct ti_write_data_bytes {
 	u8	bDataCounter;
 	__be16	wBaseAddrHi;
 	__be16	wBaseAddrLo;
-	u8	bData[0];
+	u8	bData[];
 } __packed;
 
 struct ti_read_data_request {
@@ -234,7 +234,7 @@ struct ti_read_data_bytes {
 	__u8	bCmdCode;
 	__u8	bModuleId;
 	__u8	bErrorCode;
-	__u8	bData[0];
+	__u8	bData[];
 } __packed;
 
 /* Interrupt struct */
-- 
2.25.0