[PATCH 17/18] treewide: uapi: Replace zero-length arrays with flexible-array members

[Sebastian Huber]

From: "Gustavo A. R. Silva" <gustavoars at kernel.org>

There is a regular need in the kernel to provide a way to declare
having a dynamically sized set of trailing elements in a structure.
Kernel code should always use “flexible array members”[1] for these
cases. The older style of one-element or zero-length arrays should
no longer be used[2].

This code was transformed with the help of Coccinelle:
(linux-5.19-rc2$ spatch --jobs $(getconf _NPROCESSORS_ONLN) --sp-file script.cocci --include-headers --dir . > output.patch)

@@
identifier S, member, array;
type T1, T2;
@@

struct S {
  ...
  T1 member;
  T2 array[
- 0
  ];
};

-fstrict-flex-arrays=3 is coming and we need to land these changes
to prevent issues like these in the short future:

../fs/minix/dir.c:337:3: warning: 'strcpy' will always overflow; destination buffer has size 0,
but the source string has length 2 (including NUL byte) [-Wfortify-source]
		strcpy(de3->name, ".");
		^

Since these are all [0] to [] changes, the risk to UAPI is nearly zero. If
this breaks anything, we can use a union with a new member name.

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.16/process/deprecated.html#zero-length-and-one-element-arrays

Link: https://github.com/KSPP/linux/issues/78
Build-tested-by: kernel test robot <lkp at intel.com>
Link: https://lore.kernel.org/lkml/62b675ec.wKX6AOZ6cbE71vtF%25lkp@intel.com/
Acked-by: Dan Williams <dan.j.williams at intel.com> # For ndctl.h
Signed-off-by: Gustavo A. R. Silva <gustavoars at kernel.org>
---
 cpukit/libfs/src/jffs2/include/linux/jffs2.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/cpukit/libfs/src/jffs2/include/linux/jffs2.h b/cpukit/libfs/src/jffs2/include/linux/jffs2.h
index 784ba0b969..637ee4a793 100644
--- a/cpukit/libfs/src/jffs2/include/linux/jffs2.h
+++ b/cpukit/libfs/src/jffs2/include/linux/jffs2.h
@@ -123,7 +123,7 @@ struct jffs2_raw_dirent
 	__u8 unused[2];
 	jint32_t node_crc;
 	jint32_t name_crc;
-	__u8 name[0];
+	__u8 name[];
 };
 
 /* The JFFS2 raw inode structure: Used for storage on physical media.  */
@@ -155,7 +155,7 @@ struct jffs2_raw_inode
 	jint16_t flags;	     /* See JFFS2_INO_FLAG_* */
 	jint32_t data_crc;   /* CRC for the (compressed) data.  */
 	jint32_t node_crc;   /* CRC for the raw inode (excluding data)  */
-	__u8 data[0];
+	__u8 data[];
 };
 
 struct jffs2_raw_xattr {
@@ -170,7 +170,7 @@ struct jffs2_raw_xattr {
 	jint16_t value_len;
 	jint32_t data_crc;
 	jint32_t node_crc;
-	__u8 data[0];
+	__u8 data[];
 } __attribute__((packed));
 
 struct jffs2_raw_xref
@@ -196,7 +196,7 @@ struct jffs2_raw_summary
 	jint32_t padded;	/* sum of the size of padding nodes */
 	jint32_t sum_crc;	/* summary information crc */
 	jint32_t node_crc; 	/* node crc */
-	jint32_t sum[0]; 	/* inode summary info */
+	jint32_t sum[]; 	/* inode summary info */
 };
 
 union jffs2_node_union
-- 
2.35.3