dm: replace zero-length array with flexible-array

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]

sizeof(flexible-array-member) triggers a warning because flexible array
members have incomplete type[1]. There are some instances of code in
which the sizeof operator is being incorrectly/erroneously applied to
zero-length arrays and the result is zero. Such instances may be hiding
some bugs. So, this work (flexible-array member conversions) will also
help to get completely rid of those sorts of issues.

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 7649773293 ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
This commit is contained in:
Gustavo A. R. Silva 2020-05-07 13:51:58 -05:00 committed by Mike Snitzer
parent bd5c40313a
commit b18ae8dd9d
9 changed files with 9 additions and 9 deletions

View File

@ -214,7 +214,7 @@ 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

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@ -92,7 +92,7 @@ struct journal_entry {
} s;
__u64 sector;
} u;
commit_id_t last_bytes[0];
commit_id_t last_bytes[];
/* __u8 tag[0]; */
};

View File

@ -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 {

View File

@ -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)

View File

@ -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,

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@ -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

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@ -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[];
};
/*

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@ -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,

View File

@ -38,7 +38,7 @@ struct node_header {
struct btree_node {
struct node_header header;
__le64 keys[0];
__le64 keys[];
} __packed;