James Clarke [off-list ref] writes:
Since the MBR layout only has partition records as 2-byte aligned, the 32-bit
fields in them are not aligned. Thus, they cannot be accessed on some
architectures (such as SPARC) by using a "struct MBR_part_record *" pointer,
as the compiler can assume that the pointer is properly aligned. Instead, the
records must be accessed by going through the MBR struct itself every time.
Signed-off-by: James Clarke <redacted>
---
Changes from v1:
* Added packed attribute to MBR_part_record
* Reformatted changes to fit the 80-character line limit (assuming a tab stop
of 4; if it's 8 I can try and cut the line lengths down, though with the
extra verbosity that's going to be more awkward...)
I am going to clean this up - a tab is always 8 characters just like
with the kernel.
Jes
quoted hunk
part.h | 2 +-
super-mbr.c | 6 ++++++
util.c | 15 ++++++++-------
3 files changed, 15 insertions(+), 8 deletions(-)
diff --git a/part.h b/part.h
index 862a14c..e697fb4 100644
--- a/part.h
+++ b/part.h
@@ -40,7 +40,7 @@ struct MBR_part_record {
__u8 last_cyl;
__u32 first_sect_lba;
__u32 blocks_num;
-};
+} __attribute__((packed));
struct MBR {
__u8 pad[446];diff --git a/super-mbr.c b/super-mbr.c
index 62b3f03..303dde4 100644
--- a/super-mbr.c
+++ b/super-mbr.c
@@ -57,6 +57,9 @@ static void examine_mbr(struct supertype *st, char *homehost)
printf(" MBR Magic : %04x\n", sb->magic);
for (i = 0; i < MBR_PARTITIONS; i++)
+ /* Have to make every access through sb rather than using a pointer to
+ * the partition table (or an entry), since the entries are not
+ * properly aligned. */
if (sb->parts[i].blocks_num)
printf("Partition[%d] : %12lu sectors at %12lu (type %02x)\n",
i,@@ -151,6 +154,9 @@ static void getinfo_mbr(struct supertype *st, struct mdinfo *info, char *map)
info->component_size = 0;
for (i = 0; i < MBR_PARTITIONS ; i++)
+ /* Have to make every access through sb rather than using a pointer to
+ * the partition table (or an entry), since the entries are not
+ * properly aligned. */
if (sb->parts[i].blocks_num) {
unsigned long last =
(unsigned long)__le32_to_cpu(sb->parts[i].blocks_num)diff --git a/util.c b/util.c
index a238a21..4a8767b 100644
--- a/util.c
+++ b/util.c
@@ -1412,7 +1412,6 @@ static int get_gpt_last_partition_end(int fd, unsigned long long *endofpart)
static int get_last_partition_end(int fd, unsigned long long *endofpart)
{
struct MBR boot_sect;
- struct MBR_part_record *part;
unsigned long long curr_part_end;
unsigned part_nr;
int retval = 0;@@ -1429,21 +1428,23 @@ static int get_last_partition_end(int fd, unsigned long long *endofpart)
if (boot_sect.magic == MBR_SIGNATURE_MAGIC) {
retval = 1;
/* found the correct signature */
- part = boot_sect.parts;
for (part_nr = 0; part_nr < MBR_PARTITIONS; part_nr++) {
+ /* Have to make every access through boot_sect rather than using a
+ * pointer to the partition table (or an entry), since the entries
+ * are not properly aligned. */
+
/* check for GPT type */
- if (part->part_type == MBR_GPT_PARTITION_TYPE) {
+ if (boot_sect.parts[part_nr].part_type == MBR_GPT_PARTITION_TYPE) {
retval = get_gpt_last_partition_end(fd, endofpart);
break;
}
/* check the last used lba for the current partition */
- curr_part_end = __le32_to_cpu(part->first_sect_lba) +
- __le32_to_cpu(part->blocks_num);
+ curr_part_end =
+ __le32_to_cpu(boot_sect.parts[part_nr].first_sect_lba) +
+ __le32_to_cpu(boot_sect.parts[part_nr].blocks_num);
if (curr_part_end > *endofpart)
*endofpart = curr_part_end;
-
- part++;
}
} else {
/* Unknown partition table */