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Date:   Fri, 20 Mar 2020 18:25:56 -0500
From:   "Gustavo A. R. Silva" <gustavo@embeddedor.com>
To:     Kukjin Kim <kgene@kernel.org>,
        Krzysztof Kozlowski <krzk@kernel.org>,
        Andi Shyti <andi@etezian.org>, Mark Brown <broonie@kernel.org>
Cc:     linux-arm-kernel@lists.infradead.org,
        linux-samsung-soc@vger.kernel.org, linux-spi@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Subject: [PATCH][next] spi: spi-s3c24xx: Replace zero-length array with
 flexible-array member
Message-ID: <20200320232556.GA24989@embeddedor.com>
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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
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

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@embeddedor.com>
---
 drivers/spi/spi-s3c24xx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/spi/spi-s3c24xx.c b/drivers/spi/spi-s3c24xx.c
index 2d6e37f25e2d..2cb3b611c294 100644
--- a/drivers/spi/spi-s3c24xx.c
+++ b/drivers/spi/spi-s3c24xx.c
@@ -227,7 +227,7 @@ static inline unsigned int hw_txbyte(struct s3c24xx_spi *hw, int count)
 struct spi_fiq_code {
 	u32	length;
 	u32	ack_offset;
-	u8	data[0];
+	u8	data[];
 };
 
 extern struct spi_fiq_code s3c24xx_spi_fiq_txrx;
-- 
2.23.0