On 15.07.2015 18:52, Leif Lindholm wrote:
> On Wed, Jul 15, 2015 at 05:47:50PM +0200, Vladimir 'φ-coder/phcoder'
> Serbinenko wrote:
>> Go ahead
>
> The below was more of an RFC than something committable - are you OK
> with me splitting the types.h changes out as a separate patch?
>
I've fixed this and several other bad alignments in xfs.c
>> 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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>>
>>
>
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