linux-kernel - Re: [PATCH][next] irqchip: irq-bcm7038-l1: Replace zero-length array with flexible-array member

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Message-ID: <86sgi1zqtj.wl-maz@kernel.org>
Date:   Sat, 21 Mar 2020 15:10:48 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        bcm-kernel-feedback-list@...adcom.com, linux-mips@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] irqchip: irq-bcm7038-l1: Replace zero-length array with flexible-array member

On Thu, 19 Mar 2020 21:44:38 +0000,
"Gustavo A. R. Silva" <gustavo@...eddedor.com> wrote:
> 
> 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@...eddedor.com>
> ---
>  drivers/irqchip/irq-bcm7038-l1.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Queued for 5.7.

Thanks,

	M.

-- 
Jazz is not dead, it just smells funny.