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[qemu-s390x] [PATCH v2 1/3] hw/s390x/ipl: Fix alignment problems of S390

From: Thomas Huth
Subject: [qemu-s390x] [PATCH v2 1/3] hw/s390x/ipl: Fix alignment problems of S390IPLState members
Date: Wed, 26 Sep 2018 09:38:45 +0200

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 mis-
aligned memory address.
The easiest solution to fix this problem is to move the packed structures
to the beginning of the S390IPLState. Also add some additional comments
here to prevent that this problem will be introduced again in the future.

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 
 #define S390_IPL_TYPE_FCP 0x00
 #define S390_IPL_TYPE_CCW 0x02

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