We bumped into the build error while testing gcc-10 pre-release.
In file included from ../../include/grub/file.h:22,
from ../../grub-core/fs/zfs/zfs.c:34:
../../grub-core/fs/zfs/zfs.c: In function 'zap_leaf_lookup':
../../grub-core/fs/zfs/zfs.c:2263:44: error: array subscript '<unknown>' is outside the bounds of an interior zero-length array 'grub_uint16_t[0]' {aka 'short unsigned int[0]'} [-Werror=zero-length-bounds]
2263 | for (chunk = grub_zfs_to_cpu16 (l->l_hash[LEAF_HASH (blksft, h, l)], endian);
../../include/grub/types.h:241:48: note: in definition of macro 'grub_le_to_cpu16'
241 | # define grub_le_to_cpu16(x) ((grub_uint16_t) (x))
| ^
../../grub-core/fs/zfs/zfs.c:2263:16: note: in expansion of macro 'grub_zfs_to_cpu16'
2263 | for (chunk = grub_zfs_to_cpu16 (l->l_hash[LEAF_HASH (blksft, h, l)], endian);
| ^~~~~~~~~~~~~~~~~
In file included from ../../grub-core/fs/zfs/zfs.c:48:
../../include/grub/zfs/zap_leaf.h:72:16: note: while referencing 'l_hash'
72 | grub_uint16_t l_hash[0];
| ^~~~~~
Here I'd like to quote from the gcc document [1] which seems best to
explain what is going on here.
"Although the size of a zero-length array is zero, an array member of
this kind may increase the size of the enclosing type as a result of
tail padding. The offset of a zero-length array member from the
beginning of the enclosing structure is the same as the offset of an
array with one or more elements of the same type. The alignment of a
zero-length array is the same as the alignment of its elements.
Declaring zero-length arrays in other contexts, including as interior
members of structure objects or as non-member objects, is discouraged.
Accessing elements of zero-length arrays declared in such contexts is
undefined and may be diagnosed."
The l_hash[0] is apparnetly an interior member to the enclosed structure
while l_entries[0] is the trailing member. And the offending code tries
to access members in l_hash[0] array that triggers the diagnose.
Given that the l_entries[0] is used to get proper alignment to access
leaf chunks, we can accomplish the same thing through the ALIGN_UP macro
thus eliminating l_entries[0] from the structure. In this way we can
pacify the warning as l_hash[0] now becomes the last member to the
enclosed structure.
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
Signed-off-by: Michael Chang <mchang@suse.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
large blocks basically use extensible dataset feature, or to be exact,
setting recordsize above 128k will trigger large_block feature to be
enabled and storing such blocks is using feature extensible dataset. so
the extensible dataset is prerequisite.
Changes implement read support extensible dataset… instead of fixed DMU
types they dont specify type, making it possible to use fat zap objects
from bonus area.
grub_memset should zero out padding after data end. It is not clear
why it is needed at all - ZFS block is at least 512 bytes and power
of two, so it is always multiple of 16 bytes. This grub_memset
apparently never did anything.
In the past birth was always zero for holes. This feature started
to make use of birth for holes as well, so change code to test for
valid DVA address instead.
* grub-core/fs/zfs/zfs.c (grub_zfs_device_desc): New member
max_children_ashift.
(fill_vdev_info_real): Fill max_children_ashift.
(read_device): Use max_children_ashift.
embed to take a maximum value for nsectors.
* include/grub/emu/hostdisk.h (grub_util_ldm_embed): Likewise.
* include/grub/fs.h (grub_fs): Likewise.
* grub-core/partmap/msdos.c (embed_signatures): New array.
(pc_partition_map_embed): Check for and avoid sectors matching any
of the signatures in embed_signatures, up to max_nsectors.
* grub-core/partmap/gpt.c (gpt_partition_map_embed): Restrict
returned sector map to max_nsectors.
* grub-core/disk/ldm.c (grub_util_ldm_embed): Likewise.
* grub-core/fs/btrfs.c (grub_btrfs_embed): Likewise.
* grub-core/fs/zfs/zfs.c (grub_zfs_embed): Likewise.
* util/grub-setup.c (setup): Allow for the embedding area being
split into multiple blocklists. Tell dest_partmap->embed the
maximum number of sectors we care about.
