On Tue, 2013-12-03 at 15:40 +0000, Julien Grall wrote:
> On ARM (32 bits and 64 bits), the double-word is 8-bytes aligned. This will
> result on different structure from Xen and Linux repositories.
>
> As Linux is using __packed__ attribute, it must have a 4-bytes padding before
> each "id" field.
>
> This change breaks guest block support with older kernel. IMHO, it's
> acceptable
> because Xen on ARM is still on Tech Preview and the hypercall ABI is not yet
> freezed.
>
> Only one architecture (x86_32) doesn't have 64-bit ABI for the block
> interface.
> Don't add padding if Linux is compiled for this architecture.
Konrad asked for confirmation that this didn't change x86.
Using
http://stackoverflow.com/questions/9788679/how-to-get-the-relative-adress-of-a-field-in-a-structure-dump-c
I created offsets.py as described there then for i386, amd64, arm, arm64
before and after I built with CONFIG_DEBUG_INFO but not
CONFIG_DEBUG_INFO_REDUCED then:
$ cat script
python
sys.path.insert(0, '')
import offsets
end
offsets-of "struct blkif_request"
offsets-of "struct blkif_request_rw"
offsets-of "struct blkif_request_discard"
offsets-of "struct blkif_request_other"
offsets-of "struct blkif_request_indirect"
$ gdb -x script --batch drivers/block/xen-blkfront.o
struct blkif_request {
operation => 0
u => 1
}
struct blkif_request_rw {
nr_segments => 0
handle => 1
_pad1 => 3
id => 7
sector_number => 15
seg => 23
}
struct blkif_request_discard {
flag => 0
_pad1 => 1
_pad2 => 3
id => 7
sector_number => 15
nr_sectors => 23
_pad3 => 31
}
struct blkif_request_other {
_pad1 => 0
_pad2 => 1
_pad3 => 3
id => 7
}
struct blkif_request_indirect {
indirect_op => 0
nr_segments => 1
_pad1 => 3
id => 7
sector_number => 15
handle => 23
_pad2 => 25
indirect_grefs => 27
_pad3 => 59
}
There is no difference to either x86 arch:
$ diff -q x86_32.{before,after} && echo same
same
$ diff -q x86_64.{before,after} && echo same
same
$
And crucially:
$ diff -q arm.after arm64.after && echo same
same
$ diff -q arm.after x86_64.after && echo same
same
$
Full results attached.
Ian.
struct blkif_request {
operation => 0
u => 1
}
struct blkif_request_rw {
nr_segments => 0
handle => 1
_pad1 => 3
id => 7
sector_number => 15
seg => 23
}
struct blkif_request_discard {
flag => 0
_pad1 => 1
_pad2 => 3
id => 7
sector_number => 15
nr_sectors => 23
_pad3 => 31
}
struct blkif_request_other {
_pad1 => 0
_pad2 => 1
_pad3 => 3
id => 7
}
struct blkif_request_indirect {
indirect_op => 0
nr_segments => 1
_pad1 => 3
id => 7
sector_number => 15
handle => 23
_pad2 => 25
indirect_grefs => 27
_pad3 => 59
}
struct blkif_request {
operation => 0
u => 1
}
struct blkif_request_rw {
nr_segments => 0
handle => 1
id => 3
sector_number => 11
seg => 19
}
struct blkif_request_discard {
flag => 0
_pad1 => 1
id => 3
sector_number => 11
nr_sectors => 19
_pad3 => 27
}
struct blkif_request_other {
_pad1 => 0
_pad2 => 1
id => 3
}
struct blkif_request_indirect {
indirect_op => 0
nr_segments => 1
id => 3
sector_number => 11
handle => 19
_pad2 => 21
indirect_grefs => 23
_pad3 => 55
}
struct blkif_request {
operation => 0
u => 1
}
struct blkif_request_rw {
nr_segments => 0
handle => 1
_pad1 => 3
id => 7
sector_number => 15
seg => 23
}
struct blkif_request_discard {
flag => 0
_pad1 => 1
_pad2 => 3
id => 7
sector_number => 15
nr_sectors => 23
_pad3 => 31
}
struct blkif_request_other {
_pad1 => 0
_pad2 => 1
_pad3 => 3
id => 7
}
struct blkif_request_indirect {
indirect_op => 0
nr_segments => 1
_pad1 => 3
id => 7
sector_number => 15
handle => 23
_pad2 => 25
indirect_grefs => 27
_pad3 => 59
}
struct blkif_request {
operation => 0
u => 1
}
struct blkif_request_rw {
nr_segments => 0
handle => 1
id => 3
sector_number => 11
seg => 19
}
struct blkif_request_discard {
flag => 0
_pad1 => 1
id => 3
sector_number => 11
nr_sectors => 19
_pad3 => 27
}
struct blkif_request_other {
_pad1 => 0
_pad2 => 1
id => 3
}
struct blkif_request_indirect {
indirect_op => 0
nr_segments => 1
id => 3
sector_number => 11
handle => 19
_pad2 => 21
indirect_grefs => 23
_pad3 => 55
}
struct blkif_request {
operation => 0
u => 1
}
struct blkif_request_rw {
nr_segments => 0
handle => 1
id => 3
sector_number => 11
seg => 19
}
struct blkif_request_discard {
flag => 0
_pad1 => 1
id => 3
sector_number => 11
nr_sectors => 19
_pad3 => 27
}
struct blkif_request_other {
_pad1 => 0
_pad2 => 1
id => 3
}
struct blkif_request_indirect {
indirect_op => 0
nr_segments => 1
id => 3
sector_number => 11
handle => 19
_pad2 => 21
indirect_grefs => 23
_pad3 => 55
}
struct blkif_request {
operation => 0
u => 1
}
struct blkif_request_rw {
nr_segments => 0
handle => 1
id => 3
sector_number => 11
seg => 19
}
struct blkif_request_discard {
flag => 0
_pad1 => 1
id => 3
sector_number => 11
nr_sectors => 19
_pad3 => 27
}
struct blkif_request_other {
_pad1 => 0
_pad2 => 1
id => 3
}
struct blkif_request_indirect {
indirect_op => 0
nr_segments => 1
id => 3
sector_number => 11
handle => 19
_pad2 => 21
indirect_grefs => 23
_pad3 => 55
}
struct blkif_request {
operation => 0
u => 1
}
struct blkif_request_rw {
nr_segments => 0
handle => 1
_pad1 => 3
id => 7
sector_number => 15
seg => 23
}
struct blkif_request_discard {
flag => 0
_pad1 => 1
_pad2 => 3
id => 7
sector_number => 15
nr_sectors => 23
_pad3 => 31
}
struct blkif_request_other {
_pad1 => 0
_pad2 => 1
_pad3 => 3
id => 7
}
struct blkif_request_indirect {
indirect_op => 0
nr_segments => 1
_pad1 => 3
id => 7
sector_number => 15
handle => 23
_pad2 => 25
indirect_grefs => 27
_pad3 => 59
}
struct blkif_request {
operation => 0
u => 1
}
struct blkif_request_rw {
nr_segments => 0
handle => 1
_pad1 => 3
id => 7
sector_number => 15
seg => 23
}
struct blkif_request_discard {
flag => 0
_pad1 => 1
_pad2 => 3
id => 7
sector_number => 15
nr_sectors => 23
_pad3 => 31
}
struct blkif_request_other {
_pad1 => 0
_pad2 => 1
_pad3 => 3
id => 7
}
struct blkif_request_indirect {
indirect_op => 0
nr_segments => 1
_pad1 => 3
id => 7
sector_number => 15
handle => 23
_pad2 => 25
indirect_grefs => 27
_pad3 => 59
}
