net: sched: Replace zero-length array with flexible-array member
Subsystems (4)
PATCH 1/1 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")
--- 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(-)
include/net/pkt_sched.h +1 -1
@@ -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 */
net/sched/em_ipt.c +1 -1
@@ -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 {
net/sched/em_nbyte.c +1 -1
@@ -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,
net/sched/sch_atm.c +1 -1
@@ -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 {
net/sched/sch_netem.c +1 -1
@@ -66,7 +66,7 @@struct disttable {u32 size; -s16 table[0 ]; +s16 table[]; };struct netem_sched_data {
Signature · 1 line
2.25.0
From: "Gustavo A. R. Silva" <[email protected]>
Date: Thu, 27 Feb 2020 14:58:44 -0600
Quoted 22 lines
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]
Quoted 7 lines
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] commit76497732932f("cxgb3/l2t: Fix undefined behaviour")Signed-off-by Gustavo A. R. Silva <[email protected]>
Applied, thank you.