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]>
---
drivers/hwtracing/stm/policy.c | 2 +-
drivers/hwtracing/stm/stm.h | 4 ++--
2 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/hwtracing/stm/policy.c b/drivers/hwtracing/stm/policy.c
index 4f932a419752..603b4a9969d3 100644
--- a/drivers/hwtracing/stm/policy.c
+++ b/drivers/hwtracing/stm/policy.c
@@ -34,7 +34,7 @@ struct stp_policy_node {
unsigned int first_channel;
unsigned int last_channel;
/* this is the one that's exposed to the attributes */
- unsigned char priv[0];
+ unsigned char priv[];
};
void *stp_policy_node_priv(struct stp_policy_node *pn)
diff --git a/drivers/hwtracing/stm/stm.h b/drivers/hwtracing/stm/stm.h
index 3569439d53bb..a9be49fc7a6b 100644
--- a/drivers/hwtracing/stm/stm.h
+++ b/drivers/hwtracing/stm/stm.h
@@ -23,7 +23,7 @@ void *stp_policy_node_priv(struct stp_policy_node *pn);
struct stp_master {
unsigned int nr_free;
- unsigned long chan_map[0];
+ unsigned long chan_map[];
};
struct stm_device {
@@ -42,7 +42,7 @@ struct stm_device {
const struct config_item_type *pdrv_node_type;
/* master allocation */
spinlock_t mc_lock;
- struct stp_master *masters[0];
+ struct stp_master *masters[];
};
#define to_stm_device(_d) \
