From: Adam Thomson <Adam.Thomson.Opensource@diasemi.com>
To: "Gustavo A. R. Silva" <gustavo@embeddedor.com>,
Adam Thomson <Adam.Thomson.Opensource@diasemi.com>,
Support Opensource <Support.Opensource@diasemi.com>,
Liam Girdwood <lgirdwood@gmail.com>,
Mark Brown <broonie@kernel.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] regulator: da9063: Replace zero-length array with flexible-array member
Date: Wed, 12 Feb 2020 14:56:05 +0000 [thread overview]
Message-ID: <AM6PR10MB22632DDE0CB4AC71796E9464801B0@AM6PR10MB2263.EURPRD10.PROD.OUTLOOK.COM> (raw)
In-Reply-To: <575985a9-cc82-1eae-6651-30a603f494d7@embeddedor.com>
On 12 February 2020 14:29, Gustavo A. R. Silva wrote:
> On 2/12/20 05:14, Adam Thomson wrote:
> > On 11 February 2020 23:47, 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
> >> inadvertenly introduced[3] to the codebase from now on.
> >>
> >> 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 <gustavo@embeddedor.com>
> >> ---
> >> drivers/regulator/da9063-regulator.c | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/regulator/da9063-regulator.c b/drivers/regulator/da9063-
> >> regulator.c
> >> index 2b0c7a85306a..368f8ad2a9f9 100644
> >> --- a/drivers/regulator/da9063-regulator.c
> >> +++ b/drivers/regulator/da9063-regulator.c
> >> @@ -119,7 +119,7 @@ struct da9063_regulator {
> >> struct da9063_regulators {
> >> unsigned n_regulators;
> >> /* Array size to be defined during init. Keep at end. */
> >> - struct da9063_regulator regulator[0];
> >> + struct da9063_regulator regulator[];
> >
> > Same comment as for da9062. The probe uses malloc and does not statically
> > initialise for this struct so this will break the probe.
> >
>
> 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]
>
> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
As for da9062:
Acked-by: Adam Thomson <Adam.Thomson.Opensource@diasemi.com>
>
> Thanks
> --
> Gustavo
prev parent reply other threads:[~2020-02-12 14:56 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-11 23:47 [PATCH] regulator: da9063: Replace zero-length array with flexible-array member Gustavo A. R. Silva
2020-02-12 11:14 ` Adam Thomson
2020-02-12 14:29 ` Gustavo A. R. Silva
2020-02-12 14:56 ` Adam Thomson [this message]
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