[libvirt] [PATCH] object: require maximal alignment in base class
Eric Blake
eblake at redhat.com
Thu Dec 12 23:07:26 UTC 2013
Recent changes to events (commit 8a29ffcf) resulted in new compile
failures on some targets (such as ARM OMAP5):
conf/domain_event.c: In function 'virDomainEventDispatchDefaultFunc':
conf/domain_event.c:1198:30: error: cast increases required alignment of
target type [-Werror=cast-align]
conf/domain_event.c:1314:34: error: cast increases required alignment of
target type [-Werror=cast-align]
cc1: all warnings being treated as errors
The error is due to alignment; the base class is merely aligned
to the worst of 'int' and 'void*', while the child class must
be aligned to a 'long long'. The solution is to include a
'long long' (and for good measure, a function pointer) in the
base class to ensure correct alignment regardless of what a
child class may add, but to wrap the inclusion in a union so
as to not incur any wasted space. On a typical x86_64 platform,
the base class remains 16 bytes; on i686, the base class remains
12 bytes; and on the impacted ARM platform, the base class grows
from 12 bytes to 16 bytes due to the increase of alignment from
4 to 8 bytes.
Reported by Michele Paolino and others.
* src/util/virobject.h (_virObject): Use a union to ensure that
subclasses never have stricter alignment than the parent.
* src/util/virobject.c (virObjectNew, virObjectUnref)
(virObjectRef): Adjust clients.
* src/libvirt.c (virConnectRef, virDomainRef, virNetworkRef)
(virInterfaceRef, virStoragePoolRef, virStorageVolRef)
(virNodeDeviceRef, virSecretRef, virStreamRef, virNWFilterRef)
(virDomainSnapshotRef): Likewise.
* src/qemu/qemu_monitor.c (qemuMonitorOpenInternal)
(qemuMonitorClose): Likewise.
Signed-off-by: Eric Blake <eblake at redhat.com>
---
Even though this fixes a build-breaker, I'd rather that someone
actually experiencing the build failure test that this fixes
the problem for them before I push (I don't have easy access to
hardware exhibiting the problem).
src/libvirt.c | 22 +++++++++++-----------
src/qemu/qemu_monitor.c | 4 ++--
src/util/virobject.c | 10 +++++-----
src/util/virobject.h | 16 ++++++++++++++--
4 files changed, 32 insertions(+), 20 deletions(-)
diff --git a/src/libvirt.c b/src/libvirt.c
index f01de83..d15d617 100644
--- a/src/libvirt.c
+++ b/src/libvirt.c
@@ -1563,7 +1563,7 @@ virConnectRef(virConnectPtr conn)
virDispatchError(NULL);
return -1;
}
- VIR_DEBUG("conn=%p refs=%d", conn, conn->object.refs);
+ VIR_DEBUG("conn=%p refs=%d", conn, conn->object.u.s.refs);
virObjectRef(conn);
return 0;
}
@@ -2469,7 +2469,7 @@ virDomainRef(virDomainPtr domain)
return -1;
}
- VIR_DOMAIN_DEBUG(domain, "refs=%d", domain->object.refs);
+ VIR_DOMAIN_DEBUG(domain, "refs=%d", domain->object.u.s.refs);
virObjectRef(domain);
return 0;
}
@@ -11977,7 +11977,7 @@ virNetworkRef(virNetworkPtr network)
virDispatchError(NULL);
return -1;
}
- VIR_DEBUG("network=%p refs=%d", network, network->object.refs);
+ VIR_DEBUG("network=%p refs=%d", network, network->object.u.s.refs);
virObjectRef(network);
return 0;
}
@@ -12921,7 +12921,7 @@ virInterfaceRef(virInterfacePtr iface)
virDispatchError(NULL);
return -1;
}
- VIR_DEBUG("iface=%p refs=%d", iface, iface->object.refs);
+ VIR_DEBUG("iface=%p refs=%d", iface, iface->object.u.s.refs);
virObjectRef(iface);
return 0;
}
@@ -13980,7 +13980,7 @@ virStoragePoolRef(virStoragePoolPtr pool)
virDispatchError(NULL);
return -1;
}
- VIR_DEBUG("pool=%p refs=%d", pool, pool->object.refs);
+ VIR_DEBUG("pool=%p refs=%d", pool, pool->object.u.s.refs);
virObjectRef(pool);
return 0;
}
@@ -15101,7 +15101,7 @@ virStorageVolRef(virStorageVolPtr vol)
virDispatchError(NULL);
return -1;
}
- VIR_DEBUG("vol=%p refs=%d", vol, vol->object.refs);
+ VIR_DEBUG("vol=%p refs=%d", vol, vol->object.u.s.refs);
virObjectRef(vol);
return 0;
}
@@ -15792,7 +15792,7 @@ virNodeDeviceRef(virNodeDevicePtr dev)
virDispatchError(NULL);
return -1;
}
- VIR_DEBUG("dev=%p refs=%d", dev, dev->object.refs);
+ VIR_DEBUG("dev=%p refs=%d", dev, dev->object.u.s.refs);
virObjectRef(dev);
return 0;
}
@@ -16900,7 +16900,7 @@ virSecretRef(virSecretPtr secret)
virDispatchError(NULL);
return -1;
}
- VIR_DEBUG("secret=%p refs=%d", secret, secret->object.refs);
+ VIR_DEBUG("secret=%p refs=%d", secret, secret->object.u.s.refs);
virObjectRef(secret);
return 0;
}
@@ -16994,7 +16994,7 @@ virStreamRef(virStreamPtr stream)
virDispatchError(NULL);
return -1;
}
- VIR_DEBUG("stream=%p refs=%d", stream, stream->object.refs);
+ VIR_DEBUG("stream=%p refs=%d", stream, stream->object.u.s.refs);
virObjectRef(stream);
return 0;
}
@@ -18400,7 +18400,7 @@ virNWFilterRef(virNWFilterPtr nwfilter)
virDispatchError(NULL);
return -1;
}
- VIR_DEBUG("nwfilter=%p refs=%d", nwfilter, nwfilter->object.refs);
+ VIR_DEBUG("nwfilter=%p refs=%d", nwfilter, nwfilter->object.u.s.refs);
virObjectRef(nwfilter);
return 0;
}
@@ -20699,7 +20699,7 @@ virDomainSnapshotRef(virDomainSnapshotPtr snapshot)
virDispatchError(NULL);
return -1;
}
- VIR_DEBUG("snapshot=%p, refs=%d", snapshot, snapshot->object.refs);
+ VIR_DEBUG("snapshot=%p, refs=%d", snapshot, snapshot->object.u.s.refs);
virObjectRef(snapshot);
return 0;
}
diff --git a/src/qemu/qemu_monitor.c b/src/qemu/qemu_monitor.c
index 1514715..1fa1492 100644
--- a/src/qemu/qemu_monitor.c
+++ b/src/qemu/qemu_monitor.c
@@ -821,7 +821,7 @@ qemuMonitorOpenInternal(virDomainObjPtr vm,
PROBE(QEMU_MONITOR_NEW,
"mon=%p refs=%d fd=%d",
- mon, mon->parent.parent.refs, mon->fd);
+ mon, mon->parent.parent.u.s.refs, mon->fd);
virObjectUnlock(mon);
return mon;
@@ -893,7 +893,7 @@ void qemuMonitorClose(qemuMonitorPtr mon)
virObjectLock(mon);
PROBE(QEMU_MONITOR_CLOSE,
- "mon=%p refs=%d", mon, mon->parent.parent.refs);
+ "mon=%p refs=%d", mon, mon->parent.parent.u.s.refs);
if (mon->fd >= 0) {
if (mon->watch) {
diff --git a/src/util/virobject.c b/src/util/virobject.c
index 61b5413..4f83bc1 100644
--- a/src/util/virobject.c
+++ b/src/util/virobject.c
@@ -192,9 +192,9 @@ void *virObjectNew(virClassPtr klass)
klass->objectSize - sizeof(virObject)) < 0)
return NULL;
- obj->magic = klass->magic;
+ obj->u.s.magic = klass->magic;
obj->klass = klass;
- virAtomicIntSet(&obj->refs, 1);
+ virAtomicIntSet(&obj->u.s.refs, 1);
PROBE(OBJECT_NEW, "obj=%p classname=%s", obj, obj->klass->name);
@@ -252,7 +252,7 @@ bool virObjectUnref(void *anyobj)
if (!obj)
return false;
- bool lastRef = virAtomicIntDecAndTest(&obj->refs);
+ bool lastRef = virAtomicIntDecAndTest(&obj->u.s.refs);
PROBE(OBJECT_UNREF, "obj=%p", obj);
if (lastRef) {
PROBE(OBJECT_DISPOSE, "obj=%p", obj);
@@ -265,7 +265,7 @@ bool virObjectUnref(void *anyobj)
/* Clear & poison object */
memset(obj, 0, obj->klass->objectSize);
- obj->magic = 0xDEADBEEF;
+ obj->u.s.magic = 0xDEADBEEF;
obj->klass = (void*)0xDEADBEEF;
VIR_FREE(obj);
}
@@ -289,7 +289,7 @@ void *virObjectRef(void *anyobj)
if (!obj)
return NULL;
- virAtomicIntInc(&obj->refs);
+ virAtomicIntInc(&obj->u.s.refs);
PROBE(OBJECT_REF, "obj=%p", obj);
return anyobj;
}
diff --git a/src/util/virobject.h b/src/util/virobject.h
index 3a08f10..d571b5c 100644
--- a/src/util/virobject.h
+++ b/src/util/virobject.h
@@ -36,9 +36,21 @@ typedef virObjectLockable *virObjectLockablePtr;
typedef void (*virObjectDisposeCallback)(void *obj);
+/* Most code should not play with the contents of this struct; however,
+ * the struct itself is public so that it can be embedded as the first
+ * field of a subclassed object. */
struct _virObject {
- unsigned int magic;
- int refs;
+ /* Ensure correct alignment of this and all subclasses, even on
+ * platforms where 'long long' or function pointers have stricter
+ * requirements than 'void *'. */
+ union {
+ long long dummy_align1;
+ void (*dummy_align2) (void);
+ struct {
+ unsigned int magic;
+ int refs;
+ } s;
+ } u;
virClassPtr klass;
};
--
1.8.4.2
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