linux-kernel - [PATCH] firmware: arm_scpi: replace zero-length array with flexible-array member

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Message-ID: <20200211231604.GA17274@embeddedor>
Date:   Tue, 11 Feb 2020 17:16:04 -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_scpi: 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_scpi.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/firmware/arm_scpi.c b/drivers/firmware/arm_scpi.c
index c7d06a36b23a..0bc52876c79a 100644
--- a/drivers/firmware/arm_scpi.c
+++ b/drivers/firmware/arm_scpi.c
@@ -273,12 +273,12 @@ struct scpi_drvinfo {
 struct scpi_shared_mem {
 	__le32 command;
 	__le32 status;
-	u8 payload[0];
+	u8 payload[];
 } __packed;
 
 struct legacy_scpi_shared_mem {
 	__le32 status;
-	u8 payload[0];
+	u8 payload[];
 } __packed;
 
 struct scp_capabilities {
-- 
2.25.0