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nfs: Replace zero-length array with flexible-array member

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

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
This commit is contained in:
Gustavo A. R. Silva 2020-03-09 13:24:42 -05:00 committed by Trond Myklebust
parent f5fdf1243f
commit 5601cda82b
2 changed files with 2 additions and 2 deletions
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2
fs/nfs/dir.c
View File

@ -141,7 +141,7 @@ struct nfs_cache_array {
int size;
int eof_index;
u64 last_cookie;
struct nfs_cache_array_entry array[0];
struct nfs_cache_array_entry array[];
};
typedef struct {

2
fs/nfs/nfs4proc.c
View File

@ -5550,7 +5550,7 @@ unwind:
struct nfs4_cached_acl {
int cached;
size_t len;
char data[0];
char data[];
};
static void nfs4_set_cached_acl(struct inode *inode, struct nfs4_cached_acl *acl)