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 <[email protected]>
---
fs/dlm/dlm_internal.h | 6 +++---
fs/dlm/user.c | 2 +-
2 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/fs/dlm/dlm_internal.h b/fs/dlm/dlm_internal.h
index 416d9de35679..d231ae5d2c65 100644
--- a/fs/dlm/dlm_internal.h
+++ b/fs/dlm/dlm_internal.h
@@ -421,7 +421,7 @@ struct dlm_message {
int m_bastmode;
int m_asts;
int m_result; /* 0 or -EXXX */
- char m_extra[0]; /* name or lvb */
+ char m_extra[]; /* name or lvb */
};
@@ -450,7 +450,7 @@ struct dlm_rcom {
uint64_t rc_id; /* match reply with request */
uint64_t rc_seq; /* sender's ls_recover_seq */
uint64_t rc_seq_reply; /* remote ls_recover_seq */
- char rc_buf[0];
+ char rc_buf[];
};
union dlm_packet {
@@ -506,7 +506,7 @@ struct rcom_lock {
__le16 rl_wait_type;
__le16 rl_namelen;
char rl_name[DLM_RESNAME_MAXLEN];
- char rl_lvb[0];
+ char rl_lvb[];
};
/*
diff --git a/fs/dlm/user.c b/fs/dlm/user.c
index 5264bac75115..e5cefa90b1ce 100644
--- a/fs/dlm/user.c
+++ b/fs/dlm/user.c
@@ -46,7 +46,7 @@ struct dlm_lock_params32 {
__u32 bastaddr;
__u32 lksb;
char lvb[DLM_USER_LVB_LEN];
- char name[0];
+ char name[];
};
struct dlm_write_request32 {
