linux-kernel - Re: [PATCH] PCI: hv: Replace zero-length array with flexible-array member

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Date:   Wed, 4 Mar 2020 17:55:09 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Dexuan Cui <decui@...rosoft.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:     "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>,
        "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>,
        Wei Liu <wei.liu@...nel.org>
Subject: Re: [PATCH] PCI: hv: Replace zero-length array with flexible-array
 member

On Thu, Feb 13, 2020 at 03:43:40AM +0000, Dexuan Cui wrote:
> > 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>
> 

Lorenzo, will you be picking up this patch? It seems to me you've been
handling patches to pci-hyperv.c. This patch is not yet in pci/hv branch
in your repository.

Let me know what you think.

Wei.