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Subject[PATCH][next] hwtracing: stm: stm.h: 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://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>
---
drivers/hwtracing/stm/stm.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

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) \
--
2.23.0
\
 
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