Re: [Qemu-trivial] [PATCH] kvm: Silence warning from valgrind

[Thomas Huth <thuth@redhat.com>]

On Wed, 29 Apr 2015 09:34:51 +0300
Michael Tokarev <mjt@tls.msk.ru> wrote:

> 27.04.2015 19:59, Thomas Huth wrote:
> > valgrind complains here about uninitialized bytes with the following message:
> > 
> > ==17814== Syscall param ioctl(generic) points to uninitialised byte(s)
> > ==17814==    at 0x466A780: ioctl (in /usr/lib64/power8/libc-2.17.so)
> > ==17814==    by 0x100735B7: kvm_vm_ioctl (kvm-all.c:1920)
> > ==17814==    by 0x10074583: kvm_set_ioeventfd_mmio (kvm-all.c:574)
> > 
> > Let's fix it by using a proper struct initializer in kvm_set_ioeventfd_mmio().
> > 
> > Signed-off-by: Thomas Huth <thuth@redhat.com>
> > ---
> >  kvm-all.c | 14 +++++++-------
> >  1 file changed, 7 insertions(+), 7 deletions(-)
> > 
> > diff --git a/kvm-all.c b/kvm-all.c
> > index dd44f8c..077b0ed 100644
> > --- a/kvm-all.c
> > +++ b/kvm-all.c
> > @@ -552,13 +552,13 @@ static int kvm_set_ioeventfd_mmio(int fd, hwaddr addr, uint32_t val,
> >                                    bool assign, uint32_t size, bool datamatch)
> >  {
> >      int ret;
> > -    struct kvm_ioeventfd iofd;
> > -
> > -    iofd.datamatch = datamatch ? adjust_ioeventfd_endianness(val, size) : 0;
> > -    iofd.addr = addr;
> > -    iofd.len = size;
> > -    iofd.flags = 0;
> > -    iofd.fd = fd;
> > +    struct kvm_ioeventfd iofd = {
> > +        .datamatch = datamatch ? adjust_ioeventfd_endianness(val, size) : 0,
> > +        .addr = addr,
> > +        .len = size,
> > +        .flags = 0,
> > +        .fd = fd,
> > +    };
> 
> Hm.  So, what's the difference?  The same fields are assigned the same
> values, why in first case we have some uninitialized data and in second
> case everything is initialized?  Does struct initializer zero-fills all
> other places (alignments, missing fields etc) ?

Right, the struct initializer fills the remaining fields with zeros.

> If yes, there's no need to assign zero to flags, btw ;)

True. Shall I sent a patch without that line?

 Thomas