On 26/09/2018 09:38, Thomas Huth wrote:
> The uint16_t member cu_type of struct SenseId is not naturally aligned,
> and since the struct is marked with QEMU_PACKED, this can lead to
> unaligned memory accesses - which does not work on architectures like
> Sparc. Thus remove the QEMU_PACKED here and rather copy the struct
> byte by byte when we do copy_sense_id_to_guest().
>
> Signed-off-by: Thomas Huth <th...@redhat.com>
> ---
> hw/s390x/css.c | 33 +++++++++++++++++----------------
> include/hw/s390x/css.h | 2 +-
> 2 files changed, 18 insertions(+), 17 deletions(-)
>
> diff --git a/hw/s390x/css.c b/hw/s390x/css.c
> index 5a9fe45..0e51b85 100644
> --- a/hw/s390x/css.c
> +++ b/hw/s390x/css.c
> @@ -750,20 +750,20 @@ static void sch_handle_halt_func(SubchDev *sch)
>
> }
>
> -static void copy_sense_id_to_guest(SenseId *dest, SenseId *src)
> +static void copy_sense_id_to_guest(uint8_t *dest, SenseId *src)
> {
> int i;
>
> - dest->reserved = src->reserved;
> - dest->cu_type = cpu_to_be16(src->cu_type);
> - dest->cu_model = src->cu_model;
> - dest->dev_type = cpu_to_be16(src->dev_type);
> - dest->dev_model = src->dev_model;
> - dest->unused = src->unused;
> - for (i = 0; i < ARRAY_SIZE(dest->ciw); i++) {
> - dest->ciw[i].type = src->ciw[i].type;
> - dest->ciw[i].command = src->ciw[i].command;
> - dest->ciw[i].count = cpu_to_be16(src->ciw[i].count);
> + dest[0] = src->reserved;
> + stw_be_p(dest + 1, src->cu_type);
> + dest[3] = src->cu_model;
> + stw_be_p(dest + 4, src->dev_type);
> + dest[6] = src->dev_model;
> + dest[7] = src->unused;
> + for (i = 0; i < ARRAY_SIZE(src->ciw); i++) {
> + dest[8 + i * 4] = src->ciw[i].type;
> + dest[9 + i * 4] = src->ciw[i].command;
> + stw_be_p(dest + 10 + i * 4, src->ciw[i].count);
Not really a fan of this, as we sacrifice readability due to one
unaligned member. What about only converting the unaligned members (e.g.
cu_type) from uint16_t to uint8_t[2] and adding a comment why this is
split. Then the structure is naturally packed.
We only have to fixup the places that check cu_type.
--
Thanks,
David / dhildenb
