Re: [libvirt] [PATCH] build: avoid type-punning in vbox

Am 20. April 2012 01:36 schrieb Eric Blake <eblake(a)redhat.com&gt;: > Commit 78345c68 makes at least gcc 4.1.2 on RHEL 5 complain: > > cc1: warnings being treated as errors > In file included from vbox/vbox_V4_0.c:13: > vbox/vbox_tmpl.c: In function 'vboxDomainUndefineFlags': > vbox/vbox_tmpl.c:5298: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing] > > * src/vbox/vbox_tmpl.c (vboxDomainUndefineFlags): Use union to > avoid compiler warning. > --- > > Pushing this under the build-breaker rule. > >  src/vbox/vbox_tmpl.c |    7 +++++-- >  1 files changed, 5 insertions(+), 2 deletions(-) > > diff --git a/src/vbox/vbox_tmpl.c b/src/vbox/vbox_tmpl.c > index be25828..57c18a4 100644 > --- a/src/vbox/vbox_tmpl.c > +++ b/src/vbox/vbox_tmpl.c > @@ -5294,8 +5294,11 @@ vboxDomainUndefineFlags(virDomainPtr dom, unsigned int flags) > >         ((IMachine_Delete)machine->vtbl->Delete)(machine, &safeArray, &progress); >  # else > -        vboxArray array = VBOX_ARRAY_INITIALIZER; > -        machine->vtbl->Delete(machine, 0, (IMedium**)&array, &progress); > +        union { > +            vboxArray array; > +            IMedium *medium; > +        } u = { .array = VBOX_ARRAY_INITIALIZER }; > +        machine->vtbl->Delete(machine, 0, &u.medium, &progress); >  # endif >         if (progress != NULL) { >             progress->vtbl->WaitForCompletion(progress, -1); Actually, NACK. As stated in the other mail, vboxArray is not castable to IMedium*. True, it silences the compiler any might even work by accident on XPCOM because VirtualBox might not touch the pointer beyond checking it for being non-NULL because the 0 tells it that it's an empty array. But still this is wrong and might crash on MSCOM. I might come up with a proper solution tomorrow.