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Date: Thu, 13 Feb 2020 03:43:40 +0000 From: Dexuan Cui <decui@...rosoft.com> To: "Gustavo A. R. Silva" <gustavo@...eddedor.com>, KY Srinivasan <kys@...rosoft.com>, Haiyang Zhang <haiyangz@...rosoft.com>, Stephen Hemminger <sthemmin@...rosoft.com>, Sasha Levin <sashal@...nel.org>, Lorenzo Pieralisi <lorenzo.pieralisi@....com>, Andrew Murray <amurray@...goodpenguin.co.uk>, Bjorn Helgaas <bhelgaas@...gle.com> CC: "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>, "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: RE: [PATCH] PCI: hv: Replace zero-length array with flexible-array member > From: linux-hyperv-owner@...r.kernel.org > <linux-hyperv-owner@...r.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@...rosoft.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
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