jffs2: summary.h: 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")

---
 fs/jffs2/summary.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

index 60207a2ae952..e4131cb1f1d4 100644
@@ -61,7 +61,7 @@ struct jffs2_sum_dirent_flash
 	jint32_t ino; 		/* == zero for unlink */
 	uint8_t nsize;		/* dirent name size */
 	uint8_t type;		/* dirent type */
-	uint8_t name[0];	/* dirent name */
+	uint8_t name[];	/* dirent name */
 } __attribute__((packed));
 
 struct jffs2_sum_xattr_flash

@@ -117,7 +117,7 @@ struct jffs2_sum_dirent_mem
 	jint32_t ino; 		/* == zero for unlink */
 	uint8_t nsize;		/* dirent name size */
 	uint8_t type;		/* dirent type */
-	uint8_t name[0];	/* dirent name */
+	uint8_t name[];	/* dirent name */
 } __attribute__((packed));
 
 struct jffs2_sum_xattr_mem

2.25.0


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