From: "Gustavo A. R. Silva" <gustavo@embeddedor.com> To: Mark Fasheh <mark@fasheh.com>, Joel Becker <jlbec@evilplan.org>, Joseph Qi <joseph.qi@linux.alibaba.com> Cc: ocfs2-devel@oss.oracle.com, linux-kernel@vger.kernel.org, "Gustavo A. R. Silva" <gustavo@embeddedor.com> Subject: [PATCH][next] ocfs2: cluster: Replace zero-length array with flexible-array member Date: Mon, 9 Mar 2020 15:19:07 -0500 [thread overview] Message-ID: <20200309201907.GA8005@embeddedor> (raw) 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/cluster/tcp.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/ocfs2/cluster/tcp.h b/fs/ocfs2/cluster/tcp.h index de87cbffd175..736338f45c59 100644 --- a/fs/ocfs2/cluster/tcp.h +++ b/fs/ocfs2/cluster/tcp.h @@ -32,7 +32,7 @@ struct o2net_msg __be32 status; __be32 key; __be32 msg_num; - __u8 buf[0]; + __u8 buf[]; }; typedef int (o2net_msg_handler_func)(struct o2net_msg *msg, u32 len, void *data, -- 2.25.0
WARNING: multiple messages have this Message-ID (diff)
From: Gustavo A. R. Silva <gustavo@embeddedor.com> To: Mark Fasheh <mark@fasheh.com>, Joel Becker <jlbec@evilplan.org>, Joseph Qi <joseph.qi@linux.alibaba.com> Cc: ocfs2-devel@oss.oracle.com, linux-kernel@vger.kernel.org, "Gustavo A. R. Silva" <gustavo@embeddedor.com> Subject: [Ocfs2-devel] [PATCH][next] ocfs2: cluster: Replace zero-length array with flexible-array member Date: Mon, 9 Mar 2020 15:19:07 -0500 [thread overview] Message-ID: <20200309201907.GA8005@embeddedor> (raw) 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://urldefense.com/v3/__https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html__;!!GqivPVa7Brio!NzMr-YRl2zy-K3lwLVVatz7x0uD2z7-ykQag4GrGigxmfWU8TWzDy6xrkTiW3hYl00czlw$ [2] https://urldefense.com/v3/__https://github.com/KSPP/linux/issues/21__;!!GqivPVa7Brio!NzMr-YRl2zy-K3lwLVVatz7x0uD2z7-ykQag4GrGigxmfWU8TWzDy6xrkTiW3hYHG1nAnw$ [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com> --- fs/ocfs2/cluster/tcp.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/ocfs2/cluster/tcp.h b/fs/ocfs2/cluster/tcp.h index de87cbffd175..736338f45c59 100644 --- a/fs/ocfs2/cluster/tcp.h +++ b/fs/ocfs2/cluster/tcp.h @@ -32,7 +32,7 @@ struct o2net_msg __be32 status; __be32 key; __be32 msg_num; - __u8 buf[0]; + __u8 buf[]; }; typedef int (o2net_msg_handler_func)(struct o2net_msg *msg, u32 len, void *data, -- 2.25.0
next reply other threads:[~2020-03-09 20:16 UTC|newest] Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-03-09 20:19 Gustavo A. R. Silva [this message] 2020-03-09 20:19 ` [Ocfs2-devel] [PATCH][next] ocfs2: cluster: Replace zero-length array with flexible-array member Gustavo A. R. Silva 2020-03-10 1:06 ` Joseph Qi 2020-03-10 1:06 ` [Ocfs2-devel] " Joseph Qi
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