linux-kernel - [PATCH] gpio: uniphier: Replace zero-length array with flexible-array member

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Message-ID: <20200211210618.GA29823@embeddedor>
Date:   Tue, 11 Feb 2020 15:06:18 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     linux-gpio@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: [PATCH] gpio: uniphier: 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/gpio/gpio-uniphier.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpio/gpio-uniphier.c b/drivers/gpio/gpio-uniphier.c
index 0f662b297a95..9843638d99d0 100644
--- a/drivers/gpio/gpio-uniphier.c
+++ b/drivers/gpio/gpio-uniphier.c
@@ -33,7 +33,7 @@ struct uniphier_gpio_priv {
 	struct irq_domain *domain;
 	void __iomem *regs;
 	spinlock_t lock;
-	u32 saved_vals[0];
+	u32 saved_vals[];
 };
 
 static unsigned int uniphier_gpio_bank_to_reg(unsigned int bank)
-- 
2.25.0