linux-kernel - [PATCH] firmware: arm_scmi: driver: Replace zero-length array with flexible-array member

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Message-ID: <20200211231045.GA13956@embeddedor>
Date:   Tue, 11 Feb 2020 17:10:45 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: [PATCH] firmware: arm_scmi: driver: 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/firmware/arm_scmi/driver.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
index 8f952f2f1a29..b40f71edc92d 100644
--- a/drivers/firmware/arm_scmi/driver.c
+++ b/drivers/firmware/arm_scmi/driver.c
@@ -148,7 +148,7 @@ struct scmi_shared_mem {
 #define SCMI_SHMEM_FLAG_INTR_ENABLED	BIT(0)
 	__le32 length;
 	__le32 msg_header;
-	u8 msg_payload[0];
+	u8 msg_payload[];
 };
 
 static const int scmi_linux_errmap[] = {
-- 
2.25.0