[libvirt] [PATCH 00/34] network events feature v2

[Eric Blake]

On 12/11/2013 06:18 AM, Michal Privoznik wrote:

> 
> I'm getting some compile errors on ARM:
> 
>   CC       conf/libvirt_conf_la-domain_event.lo
> conf/domain_event.c: In function 'virDomainEventDispatchDefaultFunc':
> conf/domain_event.c:1148:30: error: cast increases required alignment of
> target type [-Werror=cast-align]
>              rtcChangeEvent = (virDomainEventRTCChangePtr)event;

Hmm.  In this case, event is virObjectEventPtr, and rtcChangeEvent is
virDomainEventRTCChangePtr.  Comparing the two structs, I see the problem:

struct _virObjectEvent {
    virObject parent;
    int eventID;
    virObjectMeta meta;
};

Only has alignment specified by virObject (which in turn is unsigned
int, int, void*), int, and virObjectMeta (which in turn is int, char*,
unsigned char[]).

vs.

struct _virDomainEventRTCChange {
    virDomainEvent parent;

    long long offset;
};

I think one possible solution would be as simple as altering
src/util/virobject.h to change 'magic' from 'unsigned int' to 'unsigned
long long' - then ALL virObject structs will be forcefully aligned to
the worst case between void* and long long, so that any subclass can use
long long without requiring stricter alignment than the parent class,
and so that downcasting code like domain_event.c no longer warns.  But
it does make every object consume more memory on 64-bit platforms (from
16 bytes into 24 bytes), is that okay?

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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