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From: Dexuan Cui <decui@microsoft.com>
To: "Gustavo A. R. Silva" <gustavo@embeddedor.com>,
	KY Srinivasan <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	Sasha Levin <sashal@kernel.org>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Andrew Murray <amurray@thegoodpenguin.co.uk>,
	Bjorn Helgaas <bhelgaas@google.com>
Cc: "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
	"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] PCI: hv: Replace zero-length array with flexible-array member
Date: Thu, 13 Feb 2020 03:43:40 +0000
Message-ID: <HK0P153MB0148FB68FCBAE908CA5991C3BF1A0@HK0P153MB0148.APCP153.PROD.OUTLOOK.COM> (raw)
In-Reply-To: <20200213005048.GA9662@embeddedor.com>

> From: linux-hyperv-owner@vger.kernel.org
> <linux-hyperv-owner@vger.kernel.org> On Behalf Of Gustavo A. R. Silva
> Sent: Wednesday, February 12, 2020 4:51 PM
>  ...
> 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.

Looks good to me. Thanks, Gustavo!
 
Reviewed-by: Dexuan Cui <decui@microsoft.com>

FWIW, it looks there are a lot of more to fix in the kernel tree: the below
commands return 1373 for me:

grep -nr '\[0\];$' * | grep '\.h:' | grep -v = | wc -l

Running the commands against the kernel/ directory returns 3.

Thanks,
-- Dexuan

      reply index

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-13  0:50 Gustavo A. R. Silva
2020-02-13  3:43 ` Dexuan Cui [this message]

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