+ ocfs2-replace-zero-length-array-with-flexible-array-member.patch added to -mm tree

+ ocfs2-replace-zero-length-array-with-flexible-array-member.patch added to -mm tree

[akpm]

The patch titled
     Subject: ocfs2: replace zero-length array with flexible-array member
has been added to the -mm tree.  Its filename is
     ocfs2-replace-zero-length-array-with-flexible-array-member.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/ocfs2-replace-zero-length-array-with-flexible-array-member.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/ocfs2-replace-zero-length-array-with-flexible-array-member.patch

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------------------------------------------------------
From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Subject: 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")

Link: http://lkml.kernel.org/r/20200213160244.GA6088@embeddedor
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Acked-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Gang He <ghe@suse.com>
Cc: Jun Piao <piaojun@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

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

--- a/fs/ocfs2/journal.c~ocfs2-replace-zero-length-array-with-flexible-array-member
+++ a/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)
_

Patches currently in -mm which might be from gustavo@embeddedor.com are

ocfs2-replace-zero-length-array-with-flexible-array-member.patch
lib-bch-replace-zero-length-array-with-flexible-array-member.patch
lib-ts_bm-replace-zero-length-array-with-flexible-array-member.patch
lib-ts_fsm-replace-zero-length-array-with-flexible-array-member.patch
lib-ts_kmp-replace-zero-length-array-with-flexible-array-member.patch
gcov-gcc_4_7-replace-zero-length-array-with-flexible-array-member.patch
gcov-gcc_3_4-replace-zero-length-array-with-flexible-array-member.patch
gcov-fs-replace-zero-length-array-with-flexible-array-member.patch