Re: [PATCH RESEND] ASoC: Intel: Skylake: Replace zero-length array with flexible-array

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On 2020-05-11 7:46 PM, 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@xxxxxxxxxx>
---
  sound/soc/intel/atom/sst-atom-controls.h |    2 +-
  sound/soc/intel/skylake/skl-i2s.h        |    2 +-
  sound/soc/intel/skylake/skl-topology.h   |    4 ++--
  sound/soc/intel/skylake/skl.h            |    2 +-
  4 files changed, 5 insertions(+), 5 deletions(-)


Acked-by: Cezary Rojewski <cezary.rojewski@xxxxxxxxx>

Thanks,
Czarek



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