On Wed, 26 Sep 2018 09:38:46 +0200 Thomas Huth <[email protected]> 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 <[email protected]> > --- > 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; The doc states that byte 7 always consists of zeroes... but copying the 'unused' field is probably less magic than just writing 0. > + 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); > } > } It seems our only choice is which kind of ugly we prefer when fixing this issue... at least the usage of stw_be_p makes this look a bit better :) But maybe add a comment /* * As the SenseId struct cannot be packed (would cause unaligned * accesses), we have to copy the individual fields to an unstructured * area using the correct layout. */ so that we don't wonder why it looks like this in the future?
