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 <gustavoars@xxxxxxxxxx>
---
include/net/mac80211.h | 10 +++++-----
net/mac80211/ieee80211_i.h | 2 +-
2 files changed, 6 insertions(+), 6 deletions(-)
diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index b6b4de0e4b5e..75ff87b860a4 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -230,7 +230,7 @@ struct ieee80211_chanctx_conf {
bool radar_enabled;
- u8 drv_priv[0] __aligned(sizeof(void *));
+ u8 drv_priv[] __aligned(sizeof(void *));
};
/**
@@ -1652,7 +1652,7 @@ struct ieee80211_vif {
bool txqs_stopped[IEEE80211_NUM_ACS];
/* must be last */
- u8 drv_priv[0] __aligned(sizeof(void *));
+ u8 drv_priv[] __aligned(sizeof(void *));
};
static inline bool ieee80211_vif_is_mesh(struct ieee80211_vif *vif)
@@ -1780,7 +1780,7 @@ struct ieee80211_key_conf {
s8 keyidx;
u16 flags;
u8 keylen;
- u8 key[0];
+ u8 key[];
};
#define IEEE80211_MAX_PN_LEN 16
@@ -2035,7 +2035,7 @@ struct ieee80211_sta {
struct ieee80211_txq *txq[IEEE80211_NUM_TIDS + 1];
/* must be last */
- u8 drv_priv[0] __aligned(sizeof(void *));
+ u8 drv_priv[] __aligned(sizeof(void *));
};
/**
@@ -2081,7 +2081,7 @@ struct ieee80211_txq {
u8 ac;
/* must be last */
- u8 drv_priv[0] __aligned(sizeof(void *));
+ u8 drv_priv[] __aligned(sizeof(void *));
};
/**
diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index f8ed4f621f7f..ea483861b743 100644
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -267,7 +267,7 @@ struct probe_resp {
struct rcu_head rcu_head;
int len;
u16 csa_counter_offsets[IEEE80211_MAX_CSA_COUNTERS_NUM];
- u8 data[0];
+ u8 data[];
};
struct ps_data {
