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jfs: 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: Dave Kleikamp <dave.kleikamp@oracle.com>
This commit is contained in:
Gustavo A. R. Silva 2020-03-09 13:23:08 -05:00 committed by Dave Kleikamp
parent 2c523b344d
commit 7aba5dcc23
2 changed files with 3 additions and 3 deletions
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2
fs/jfs/jfs_dtree.c
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@ -2964,7 +2964,7 @@ struct jfs_dirent {
loff_t position;
int ino;
u16 name_len;
char name[0];
char name[];
};
/*

4
fs/jfs/jfs_xattr.h
View File

@ -17,12 +17,12 @@ struct jfs_ea {
u8 flag; /* Unused? */
u8 namelen; /* Length of name */
__le16 valuelen; /* Length of value */
char name[0]; /* Attribute name (includes null-terminator) */
char name[]; /* Attribute name (includes null-terminator) */
}; /* Value immediately follows name */
struct jfs_ea_list {
__le32 size; /* overall size */
struct jfs_ea ea[0]; /* Variable length list */
struct jfs_ea ea[]; /* Variable length list */
};
/* Macros for defining maxiumum number of bytes supported for EAs */