linux-kernel - [PATCH] hwmon: (ibmaem) Replace zero-length array with flexible-array member

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Message-ID: <20200211234237.GA26971@embeddedor>
Date:   Tue, 11 Feb 2020 17:42:37 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Jean Delvare <jdelvare@...e.com>,
        Guenter Roeck <linux@...ck-us.net>
Cc:     linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: [PATCH] hwmon: (ibmaem) 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/hwmon/ibmaem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/hwmon/ibmaem.c b/drivers/hwmon/ibmaem.c
index db63c1295cb2..fb052c2d9c34 100644
--- a/drivers/hwmon/ibmaem.c
+++ b/drivers/hwmon/ibmaem.c
@@ -232,7 +232,7 @@ struct aem_read_sensor_req {
 
 struct aem_read_sensor_resp {
 	struct aem_iana_id	id;
-	u8			bytes[0];
+	u8			bytes[];
 } __packed;
 
 /* Data structures to talk to the IPMI layer */
-- 
2.25.0