On 8/13/15 4:26 AM, Jan Kara wrote:
> struct xfs_attr_leafblock contains 'entries' array which is declared
> with size 1 altough it can in fact contain much more entries. Since this
> array is followed by further struct members, gcc (at least in version
> 4.8.3) thinks that the array has the fixed size of 1 element and thus
> may optimize away all accesses beyond the end of array resulting in
> non-working code. This problem was only observed with userspace code in
> xfsprogs, however it's better to be safe in kernel as well and have
> matching kernel and xfsprogs definitions.
>
> Signed-off-by: Jan Kara <jack@xxxxxxxx>
> ---
> fs/xfs/libxfs/xfs_da_format.h | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> This is a kernel version of the xfsprogs patch I've sent a while ago.
>
> diff --git a/fs/xfs/libxfs/xfs_da_format.h b/fs/xfs/libxfs/xfs_da_format.h
> index 74bcbabfa523..b14bbd6bb05f 100644
> --- a/fs/xfs/libxfs/xfs_da_format.h
> +++ b/fs/xfs/libxfs/xfs_da_format.h
> @@ -680,8 +680,15 @@ typedef struct xfs_attr_leaf_name_remote {
> typedef struct xfs_attr_leafblock {
> xfs_attr_leaf_hdr_t hdr; /* constant-structure header block */
> xfs_attr_leaf_entry_t entries[1]; /* sorted on key, not name */
> - xfs_attr_leaf_name_local_t namelist; /* grows from bottom of buf */
> - xfs_attr_leaf_name_remote_t valuelist; /* grows from bottom of buf */
> + /*
> + * The rest of the block contains the following structures after the
> + * leaf entries, growing from the bottom up. The variables are never
> + * referenced and definining them can actually make gcc optimize away
Nitpick, s/definining/defining/, maybe can be fixed on commit :)
Don't we have other similar constructs elsewhere? Do they suffer the same
fate?
... looks ...
I guess not; the other ones have the variable length array as the last member.
-Eric
> + * accesses to the 'entries' array above index 0 so don't do that.
> + *
> + * xfs_attr_leaf_name_local_t namelist;
> + * xfs_attr_leaf_name_remote_t valuelist;
> + */
> } xfs_attr_leafblock_t;
>
> /*
>
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