Go ahead
On 07.07.2015 19:17, Leif Lindholm wrote:
> On Fri, Jul 03, 2015 at 10:05:47PM +0300, Andrei Borzenkov wrote:
>> I do not claim I understand why clang complains, but this patch does
>> fix it.
>>
>> fs/xfs.c:452:25: error: cast from 'struct grub_xfs_btree_node *' to
>> 'grub_uint64_t *' (aka 'unsigned long long *') increases required
>> alignment from 1 to 8 [-Werror,-Wcast-align]
>> grub_uint64_t *keys = (grub_uint64_t *)(leaf + 1);
>> ^~~~~~~~~~~~~~~~~~~~~~~~~~~
>> 1 error generated.
>>
>> ---
>>
>> Jan, do you have any idea what's wrong and whether this is proper fix?
>> Or should I raise it with clang?
>
> Well, the problem is that struct grub_xfs_btree_node is defined with
> GRUB_PACKED - forcing a 1-byte alignment requirement as opposed to the
> 8-byte requirement that would naturally be enforced by the struct
> contents. And apparently clang objects to this, whereas gcc thinks
> everything is fine ... even though -Wcast-align is explicitly used.
>
> Now, grub_xfs_btree_keys() is only called by grub_xfs_read_block(),
> where it is immediately stuffed back into another 8-byte aligned
> pointer. And then the alignment is immediately discarded again by
> casting it to a (char *) for an arithmetic operation.
>
> If the alignment is indeed not required, it may be worth explicitly
> marking that pointer as one to a potentially unaligned location.
> But we don't currently appear to have a GRUB_UNALIGNED macro, to match
> the GRUB_PACKED for structs. Should we?
>
> If so, something like the following could be added to your patch for a
> more complete fix:
> --- a/grub-core/fs/xfs.c
> +++ b/grub-core/fs/xfs.c
> @@ -488,7 +488,7 @@ grub_xfs_read_block (grub_fshelp_node_t node,
> grub_disk_addr_t fileblock)
> if (node->inode.format == XFS_INODE_FORMAT_BTREE)
> {
> struct grub_xfs_btree_root *root;
> - const grub_uint64_t *keys;
> + const grub_uint64_t *keys GRUB_UNALIGNED;
> int recoffset;
>
> leaf = grub_malloc (node->data->bsize);
> diff --git a/include/grub/types.h b/include/grub/types.h
> index e732efb..720e236 100644
> --- a/include/grub/types.h
> +++ b/include/grub/types.h
> @@ -30,6 +30,8 @@
> #define GRUB_PACKED __attribute__ ((packed))
> #endif
>
> +#define GRUB_UNALIGNED __attribute__ ((aligned (1)))
> +
> #ifdef GRUB_BUILD
> # define GRUB_CPU_SIZEOF_VOID_P BUILD_SIZEOF_VOID_P
> # define GRUB_CPU_SIZEOF_LONG BUILD_SIZEOF_LONG
>
> /
> Leif
>
>> grub-core/fs/xfs.c | 6 +++---
>> 1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/grub-core/fs/xfs.c b/grub-core/fs/xfs.c
>> index 7249291..ea8cf7e 100644
>> --- a/grub-core/fs/xfs.c
>> +++ b/grub-core/fs/xfs.c
>> @@ -445,14 +445,14 @@ grub_xfs_next_de(struct grub_xfs_data *data, struct
>> grub_xfs_dir2_entry *de)
>> return (struct grub_xfs_dir2_entry *)(((char *)de) + ALIGN_UP(size, 8));
>> }
>>
>> -static grub_uint64_t *
>> +static void *
>> grub_xfs_btree_keys(struct grub_xfs_data *data,
>> struct grub_xfs_btree_node *leaf)
>> {
>> - grub_uint64_t *keys = (grub_uint64_t *)(leaf + 1);
>> + char *keys = (char *)leaf + sizeof (*leaf);
>>
>> if (data->hascrc)
>> - keys += 6; /* skip crc, uuid, ... */
>> + keys += 6 * sizeof (grub_uint64_t); /* skip crc, uuid, ... */
>> return keys;
>> }
>>
>> --
>> tg: (7a21030..) u/xfs-clang-align (depends on: master)
>>
>> _______________________________________________
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>> Grub-devel@gnu.org
>> https://lists.gnu.org/mailman/listinfo/grub-devel
>
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