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    SubjectRe: [PATCH] staging: greybus: Replace zero-length array with flexible-array
    On Wed, May 13, 2020 at 05:03:43PM +0200, Johan Hovold wrote:
    > On Thu, May 07, 2020 at 01:53:18PM -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>
    > > ---
    > > drivers/greybus/arpc.h | 2 -
    > > include/linux/greybus/greybus_protocols.h | 44 +++++++++++++++---------------
    >
    > I noticed Greg just applied this one to his -testing branch, but do we
    > really want this in greybus_protocols.h, which is meant to be shared
    > with the firmware side? Perhaps not an issue, just figured I'd point
    > this out.

    Why not, it should be the same thing, right? No logic has changed that
    I see.

    thanks,

    greg k-h

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