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

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Message-ID: <20200304180635.GA21844@e121166-lin.cambridge.arm.com>
Date:   Wed, 4 Mar 2020 18:06:35 +0000
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Wei Liu <wei.liu@...nel.org>
Cc:     Dexuan Cui <decui@...rosoft.com>,
        "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>,
        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>
Subject: Re: [PATCH] PCI: hv: Replace zero-length array with flexible-array
 member

On Wed, Mar 04, 2020 at 05:55:09PM +0000, Wei Liu wrote:
> 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.

I shall pick it up, I checked patchwork and it was erroneously
assigned to Bjorn, that's why I have not taken it yet.

Fixed now, apologies, I will merge it shortly.

Lorenzo