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Subject[PATCH][next] net: sched: 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>
---
include/net/pkt_sched.h | 2 +-
net/sched/em_ipt.c | 2 +-
net/sched/em_nbyte.c | 2 +-
net/sched/sch_atm.c | 2 +-
net/sched/sch_netem.c | 2 +-
5 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h
index 6a70845bd9ab..20d2c6419612 100644
--- a/include/net/pkt_sched.h
+++ b/include/net/pkt_sched.h
@@ -181,7 +181,7 @@ struct tc_taprio_qopt_offload {
u64 cycle_time_extension;

size_t num_entries;
- struct tc_taprio_sched_entry entries[0];
+ struct tc_taprio_sched_entry entries[];
};

/* Reference counting */
diff --git a/net/sched/em_ipt.c b/net/sched/em_ipt.c
index 9fff6480acc6..eecfe072c508 100644
--- a/net/sched/em_ipt.c
+++ b/net/sched/em_ipt.c
@@ -22,7 +22,7 @@ struct em_ipt_match {
const struct xt_match *match;
u32 hook;
u8 nfproto;
- u8 match_data[0] __aligned(8);
+ u8 match_data[] __aligned(8);
};

struct em_ipt_xt_match {
diff --git a/net/sched/em_nbyte.c b/net/sched/em_nbyte.c
index 88c7ce42df7e..2c1192a2ee5e 100644
--- a/net/sched/em_nbyte.c
+++ b/net/sched/em_nbyte.c
@@ -16,7 +16,7 @@

struct nbyte_data {
struct tcf_em_nbyte hdr;
- char pattern[0];
+ char pattern[];
};

static int em_nbyte_change(struct net *net, void *data, int data_len,
diff --git a/net/sched/sch_atm.c b/net/sched/sch_atm.c
index f4f9b8cdbffb..ee12ca9f55b4 100644
--- a/net/sched/sch_atm.c
+++ b/net/sched/sch_atm.c
@@ -58,7 +58,7 @@ struct atm_flow_data {
struct atm_flow_data *excess; /* flow for excess traffic;
NULL to set CLP instead */
int hdr_len;
- unsigned char hdr[0]; /* header data; MUST BE LAST */
+ unsigned char hdr[]; /* header data; MUST BE LAST */
};

struct atm_qdisc_data {
diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index 42e557d48e4e..84f82771cdf5 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -66,7 +66,7 @@

struct disttable {
u32 size;
- s16 table[0];
+ s16 table[];
};

struct netem_sched_data {
--
2.25.0
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