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    Subject[PATCH] ocfs2: Replace zero-length array with flexible-array member
    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.

    [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>
    ---
    fs/ocfs2/journal.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/fs/ocfs2/journal.c b/fs/ocfs2/journal.c
    index 68ba354cf361..b425f0b01dce 100644
    --- a/fs/ocfs2/journal.c
    +++ b/fs/ocfs2/journal.c
    @@ -91,7 +91,7 @@ enum ocfs2_replay_state {
    struct ocfs2_replay_map {
    unsigned int rm_slots;
    enum ocfs2_replay_state rm_state;
    - unsigned char rm_replay_slots[0];
    + unsigned char rm_replay_slots[];
    };

    static void ocfs2_replay_map_set_state(struct ocfs2_super *osb, int state)
    --
    2.25.0
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