Re: [Qemu-devel] [PATCH v3 1/3] hw/s390x/ipl: Fix alignment problems of S390IPLState members

[David Hildenbrand]

On 27/09/2018 10:23, Thomas Huth wrote:
> The IplParameterBlock and QemuIplParameters structures are declared with
> QEMU_PACKED, so the compiler assumes that the structures do not need to
> be aligned in memory. Since the are listed after a "bool" within the
> S390IPLState, the IplParameterBlock and QemuIplParameters are also indeed
> mis-aligned in memory. This causes problems on Sparc during migration, since
> we use VMSTATE_UINT16 in vmstate_iplb to access the devno member for example,
> and the corresponding migration functions (like qemu_get_be16s) then try to
> access a 16-bit value from a misaligned memory address.
> The easiest solution to fix this problem is to move the packed structures
> to the beginning of the S390IPLState, right after the DeviceState of course
> which has to stay first for QOM reasons. But since DeviceState is a non-packed
> struct, we can be sure that it will be padded to the correct alignment at the
> end. If not, the QEMU_BUILD_BUG_MSG in this patch will tell us.
> 
> Signed-off-by: Thomas Huth <address@hidden>
> ---
>  hw/s390x/ipl.h | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/s390x/ipl.h b/hw/s390x/ipl.h
> index 4e87b89..b3a07a1 100644
> --- a/hw/s390x/ipl.h
> +++ b/hw/s390x/ipl.h
> @@ -132,15 +132,15 @@ typedef struct QemuIplParameters QemuIplParameters;
>  struct S390IPLState {
>      /*< private >*/
>      DeviceState parent_obj;
> +    IplParameterBlock iplb;
> +    QemuIplParameters qipl;
>      uint64_t start_addr;
>      uint64_t compat_start_addr;
>      uint64_t bios_start_addr;
>      uint64_t compat_bios_start_addr;
>      bool enforce_bios;
> -    IplParameterBlock iplb;
>      bool iplb_valid;
>      bool netboot;
> -    QemuIplParameters qipl;
>      /* reset related properties don't have to be migrated or reset */
>      enum s390_reset reset_type;
>      int reset_cpu_index;
> @@ -157,6 +157,7 @@ struct S390IPLState {
>      bool iplbext_migration;
>  };
>  typedef struct S390IPLState S390IPLState;
> +QEMU_BUILD_BUG_MSG(offsetof(S390IPLState, iplb) & 3, "alignment of iplb 
> wrong");
>  
>  #define S390_IPL_TYPE_FCP 0x00
>  #define S390_IPL_TYPE_CCW 0x02
> 
Reviewed-by: David Hildenbrand <address@hidden>

-- 

Thanks,

David / dhildenb