From: Leon Romanovsky <leon@kernel.org>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>,
Tariq Toukan <tariqt@mellanox.com>,
netdev@vger.kernel.org, linux-rdma@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] IB/mlx4: Replace zero-length array with flexible-array
Date: Wed, 13 May 2020 21:37:49 +0300 [thread overview]
Message-ID: <20200513183749.GZ4814@unreal> (raw)
In-Reply-To: <20200513183335.GB29202@ziepe.ca>
On Wed, May 13, 2020 at 03:33:35PM -0300, Jason Gunthorpe wrote:
> On Thu, May 07, 2020 at 01:59:21PM -0500, Gustavo A. R. Silva 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]
> >
> > sizeof(flexible-array-member) triggers a warning because flexible array
> > members have incomplete type[1]. There are some instances of code in
> > which the sizeof operator is being incorrectly/erroneously applied to
> > zero-length arrays and the result is zero. Such instances may be hiding
> > some bugs. So, this work (flexible-array member conversions) will also
> > help to get completely rid of those sorts of issues.
> >
> > 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 <gustavoars@kernel.org>
> > ---
> > include/linux/mlx4/qp.h | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
>
> Applied to for-next, thanks
Jason,
Please be cautious here, Jakub already applied this patch.
https://lore.kernel.org/lkml/20200509205151.209bdc9d@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com/
>
> Jason
prev parent reply other threads:[~2020-05-13 18:37 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-07 18:59 [PATCH] IB/mlx4: Replace zero-length array with flexible-array Gustavo A. R. Silva
2020-05-10 3:51 ` Jakub Kicinski
2020-05-13 18:43 ` Jason Gunthorpe
2020-05-13 18:49 ` Jakub Kicinski
2020-05-13 18:33 ` Jason Gunthorpe
2020-05-13 18:37 ` Leon Romanovsky [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200513183749.GZ4814@unreal \
--to=leon@kernel.org \
--cc=gustavoars@kernel.org \
--cc=jgg@ziepe.ca \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-rdma@vger.kernel.org \
--cc=netdev@vger.kernel.org \
--cc=tariqt@mellanox.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).