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

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Message-ID: <20200211231252.GA14830@embeddedor>
Date:   Tue, 11 Feb 2020 17:12:52 -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: perf: 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/perf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/firmware/arm_scmi/perf.c b/drivers/firmware/arm_scmi/perf.c
index 3c8ae7cc35de..8f79a98041c4 100644
--- a/drivers/firmware/arm_scmi/perf.c
+++ b/drivers/firmware/arm_scmi/perf.c
@@ -84,7 +84,7 @@ struct scmi_msg_resp_perf_describe_levels {
 		__le32 power;
 		__le16 transition_latency_us;
 		__le16 reserved;
-	} opp[0];
+	} opp[];
 };
 
 struct perf_dom_info {
-- 
2.25.0