On Tue, Nov 14, 2023 at 03:38:05PM +0100, Philippe Mathieu-Daudé wrote:
> Except imported source files, QEMU code base uses
> the QEMU_ALIGNED() macro to align its structures.
This patch only convert the alignment, but discard pack. We need both or
the struct is changed.
> ---
> hw/block/xen_blkif.h | 8 +++-----
> 1 file changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/hw/block/xen_blkif.h b/hw/block/xen_blkif.h
> index 99733529c1..c1d154d502 100644
> --- a/hw/block/xen_blkif.h
> +++ b/hw/block/xen_blkif.h
> @@ -18,7 +18,6 @@ struct blkif_common_response {
> };
>
> /* i386 protocol version */
> -#pragma pack(push, 4)
> struct blkif_x86_32_request {
> uint8_t operation; /* BLKIF_OP_??? */
> uint8_t nr_segments; /* number of segments */
> @@ -26,7 +25,7 @@ struct blkif_x86_32_request {
> uint64_t id; /* private guest value, echoed in resp */
> blkif_sector_t sector_number; /* start sector idx on disk (r/w only) */
> struct blkif_request_segment seg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> -};
> +} QEMU_ALIGNED(4);
E.g. for this one, I've compare the output of
`pahole --class_name=blkif_x86_32_request build/qemu-system-i386`:
--- before
+++ after
@@ -1,11 +1,15 @@
struct blkif_x86_32_request {
uint8_t operation; /* 0 1 */
uint8_t nr_segments; /* 1 1 */
uint16_t handle; /* 2 2 */
- uint64_t id; /* 4 8 */
- uint64_t sector_number; /* 12 8 */
- struct blkif_request_segment seg[11]; /* 20 88 */
- /* size: 108, cachelines: 2, members: 6 */
- /* last cacheline: 44 bytes */
-} __attribute__((__packed__));
+ /* XXX 4 bytes hole, try to pack */
+
+ uint64_t id; /* 8 8 */
+ uint64_t sector_number; /* 16 8 */
+ struct blkif_request_segment seg[11]; /* 24 88 */
+
+ /* size: 112, cachelines: 2, members: 6 */
+ /* sum members: 108, holes: 1, sum holes: 4 */
+ /* last cacheline: 48 bytes */
+} __attribute__((__aligned__(8)));
Thanks,
--
Anthony PERARD
