On 6/3/20 5:22 AM, Daniel P. Berrangé wrote:
Forcing 8-byte alignment on virObjectEventPtr removes the alignment increase during casts to subclasses.
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com> ---
Technically a build-breaker, but since we don't have any existing usage of __attribute__((aligned)), I wanted to get a second opinion on this approach.
One alternative approach would be to switch one of the current "int" fields in virObjectEvent to "long long".
-struct _virObjectEvent { +struct __attribute__((aligned(4))) _virObjectEvent { virObject parent; int eventID; virObjectMeta meta;
As in this, although it makes the struct larger on 32-bit platforms (which may in turn affect cache usage): struct _virObjectEvent { virObject parent; long long eventID; ... Another possibility: use the extension of unnamed unions (but if we're going to rely on gcc extensions, __attribute__ is nicer than unnamed unions): struct _virObjectEvent { union { virObject parent; long long alignment_; }; int eventID; ... We already limit ourselves to gcc and clang because of __attribute__((cleanup)), so I don't see any problem with your approach. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org