From: "Gustavo A. R. Silva" <gustavo@xxxxxxxxxxxxxx>
Subject: ocfs2: dlm: 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://urldefense.com/v3/__https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html__;!!GqivPVa7Brio!OVOYL_CouISa5L1Lw-20EEFQntw6cKMx-j8UdY4z78uYgzKBUFcfpn50GaurvbV5v7YiUA$
[2] https://urldefense.com/v3/__https://github.com/KSPP/linux/issues/21__;!!GqivPVa7Brio!OVOYL_CouISa5L1Lw-20EEFQntw6cKMx-j8UdY4z78uYgzKBUFcfpn50GaurvbXs8Eh8eg$
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
Link: http://lkml.kernel.org/r/20200309202016.GA8210@embeddedor
Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
Acked-by: Joseph Qi <joseph.qi@xxxxxxxxxxxxxxxxx>
Cc: Mark Fasheh <mark@xxxxxxxxxx>
Cc: Joel Becker <jlbec@xxxxxxxxxxxx>
Cc: Junxiao Bi <junxiao.bi@xxxxxxxxxx>
Cc: Changwei Ge <gechangwei@xxxxxxx>
Cc: Gang He <ghe@xxxxxxxx>
Cc: Jun Piao <piaojun@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/ocfs2/dlm/dlmcommon.h | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
--- a/fs/ocfs2/dlm/dlmcommon.h~ocfs2-dlm-replace-zero-length-array-with-flexible-array-member
+++ a/fs/ocfs2/dlm/dlmcommon.h
@@ -564,7 +564,7 @@ struct dlm_migratable_lockres
// 48 bytes
u8 lvb[DLM_LVB_LEN];
// 112 bytes
- struct dlm_migratable_lock ml[0]; // 16 bytes each, begins at byte 112
+ struct dlm_migratable_lock ml[]; // 16 bytes each, begins at byte 112
};
#define DLM_MIG_LOCKRES_MAX_LEN \
(sizeof(struct dlm_migratable_lockres) + \
@@ -601,7 +601,7 @@ struct dlm_convert_lock
u8 name[O2NM_MAX_NAME_LEN];
- s8 lvb[0];
+ s8 lvb[];
};
#define DLM_CONVERT_LOCK_MAX_LEN (sizeof(struct dlm_convert_lock)+DLM_LVB_LEN)
@@ -616,7 +616,7 @@ struct dlm_unlock_lock
u8 name[O2NM_MAX_NAME_LEN];
- s8 lvb[0];
+ s8 lvb[];
};
#define DLM_UNLOCK_LOCK_MAX_LEN (sizeof(struct dlm_unlock_lock)+DLM_LVB_LEN)
@@ -632,7 +632,7 @@ struct dlm_proxy_ast
u8 name[O2NM_MAX_NAME_LEN];
- s8 lvb[0];
+ s8 lvb[];
};
#define DLM_PROXY_AST_MAX_LEN (sizeof(struct dlm_proxy_ast)+DLM_LVB_LEN)
_
