From 7aba5dcc234635b44b2781dbc268048cfba388ad Mon Sep 17 00:00:00 2001 From: "Gustavo A. R. Silva" Date: Mon, 9 Mar 2020 13:23:08 -0500 Subject: [PATCH] jfs: 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") Signed-off-by: Gustavo A. R. Silva Signed-off-by: Dave Kleikamp --- fs/jfs/jfs_dtree.c | 2 +- fs/jfs/jfs_xattr.h | 4 ++-- 2 files changed, 3 insertions(+), 3 deletions(-) diff --git a/fs/jfs/jfs_dtree.c b/fs/jfs/jfs_dtree.c index 3acc954f7c04..837d42f61464 100644 --- a/fs/jfs/jfs_dtree.c +++ b/fs/jfs/jfs_dtree.c @@ -2964,7 +2964,7 @@ struct jfs_dirent { loff_t position; int ino; u16 name_len; - char name[0]; + char name[]; }; /* diff --git a/fs/jfs/jfs_xattr.h b/fs/jfs/jfs_xattr.h index f0558b3348da..c50167a7bc50 100644 --- a/fs/jfs/jfs_xattr.h +++ b/fs/jfs/jfs_xattr.h @@ -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 */