md: Replace zero-length array with flexible-array member
Subsystems (2)
PATCH 1/1 md: 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")
--- drivers/md/dm-crypt.c | 2 +- drivers/md/dm-integrity.c | 2 +- drivers/md/dm-log-writes.c | 2 +- drivers/md/dm-raid.c | 2 +- drivers/md/dm-raid1.c | 2 +- drivers/md/dm-stats.c | 2 +- drivers/md/dm-stripe.c | 2 +- drivers/md/dm-switch.c | 2 +- drivers/md/md-linear.h | 2 +- drivers/md/persistent-data/dm-btree-internal.h | 2 +- drivers/md/raid1.h | 2 +- drivers/md/raid10.h | 2 +- 12 files changed, 12 insertions(+), 12 deletions(-)
drivers/md/dm-crypt.c +1 -1
@@ -212,7 +212,7 @@ struct crypt_config {struct mutex bio_alloc_lock;u8 *authenc_key;/* space for keys in authenc() format (if used) */ -u8 key[0 ]; +u8 key[]; };#define MIN_IOS 64
drivers/md/dm-integrity.c +1 -1
@@ -89,7 +89,7 @@ struct journal_entry { } s;__u64 sector; } u; -commit_id_t last_bytes[0 ]; +commit_id_t last_bytes[];/* __u8 tag[0]; */ };
drivers/md/dm-log-writes.c +1 -1
@@ -127,7 +127,7 @@ struct pending_block {char *data;u32 datalen;struct list_head list; -struct bio_vec vecs[0 ]; +struct bio_vec vecs[]; };struct per_bio_data {
drivers/md/dm-raid.c +1 -1
@@ -254,7 +254,7 @@ struct raid_set {int mode; } journal_dev; -struct raid_dev dev[0 ]; +struct raid_dev dev[]; };static void rs_config_backup (struct raid_set *rs,struct rs_layout *l)
drivers/md/dm-raid1.c +1 -1
@@ -83,7 +83,7 @@ struct mirror_set {struct work_struct trigger_event;unsigned nr_mirrors; -struct mirror mirror[0 ]; +struct mirror mirror[]; }; DECLARE_DM_KCOPYD_THROTTLE_WITH_MODULE_PARM(raid1_resync_throttle,
drivers/md/dm-stats.c +1 -1
@@ -56,7 +56,7 @@ struct dm_stat {size_t percpu_alloc_size;size_t histogram_alloc_size;struct dm_stat_percpu *stat_percpu[NR_CPUS ]; -struct dm_stat_shared stat_shared[0 ]; +struct dm_stat_shared stat_shared[]; };#define STAT_PRECISE_TIMESTAMPS 1
drivers/md/dm-stripe.c +1 -1
@@ -41,7 +41,7 @@ struct stripe_c {/* Work struct used for triggering events*/ struct work_struct trigger_event; -struct stripe stripe[0 ]; +struct stripe stripe[]; };/*
drivers/md/dm-switch.c +1 -1
@@ -53,7 +53,7 @@ struct switch_ctx {/* * Array of dm devices to switch between. */ -struct switch_path path_list[0 ]; +struct switch_path path_list[]; }; static struct switch_ctx *alloc_switch_ctx(struct dm_target *ti, unsigned nr_paths,
drivers/md/md-linear.h +1 -1
@@ -12,6 +12,6 @@ struct linear_confstruct rcu_head rcu;sector_t array_sectors;int raid_disks;/* a copy of mddev->raid_disks */ - struct dev_info disks[0]; + struct dev_info disks[]; };#endif
drivers/md/persistent-data/dm-btree-internal.h +1 -1
@@ -38,7 +38,7 @@ struct node_header {struct btree_node {struct node_header header; -__le64 keys[0 ]; +__le64 keys[]; } __packed;
drivers/md/raid1.h +1 -1
@@ -180,7 +180,7 @@ struct r1bio {* if the IO is in WRITE direction, then multiple bios are used. * We choose the number when they are allocated. */ -struct bio *bios[0 ]; +struct bio *bios[];/* DO NOT PUT ANY NEW FIELDS HERE - bios array is contiguously alloced*/ };
drivers/md/raid10.h +1 -1
@@ -153,7 +153,7 @@ struct r10bio { };sector_t addr;int devnum; - } devs[0 ]; + } devs[]; };/* bits for r10bio.state */
Signature · 1 line
2.25.0
Song Liu
maintainerQuoted 23 lines · Gustavo A. R. Silva
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]>
For md part: Acked-by: Song Liu <[email protected]>
Alasdair and Mike, would you like to route the patch via dm tree?
Thanks,
Song