libnvdimm/region: 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>
Link: https://lore.kernel.org/r/20200319230937.GA16648@embeddedor.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
diff --git a/drivers/nvdimm/nd.h b/drivers/nvdimm/nd.h
index c9f6a5b..2cf77bc 100644
--- a/drivers/nvdimm/nd.h
+++ b/drivers/nvdimm/nd.h
@@ -39,7 +39,7 @@ struct nd_region_data {
int ns_count;
int ns_active;
unsigned int hints_shift;
- void __iomem *flush_wpq[0];
+ void __iomem *flush_wpq[];
};
static inline void __iomem *ndrd_get_flush_wpq(struct nd_region_data *ndrd,
@@ -156,7 +156,7 @@ struct nd_region {
struct nd_interleave_set *nd_set;
struct nd_percpu_lane __percpu *lane;
int (*flush)(struct nd_region *nd_region, struct bio *bio);
- struct nd_mapping mapping[0];
+ struct nd_mapping mapping[];
};
struct nd_blk_region {