Re: [Qemu-devel] [PATCH] virtio: fix vring_align() on 64-bit win32 platforms

[Andrew Baumann]

> From: Eric Blake [mailto:address@hidden
> Sent: Tuesday, 21 March 2017 15:52
> 
> On 03/21/2017 05:31 PM, Andrew Baumann wrote:
> > "long" is 32-bits on win32, but we need to promote it to a 64-bit hwaddr
> > before negating, or else the top half of the address is truncated
> >
> > Signed-off-by: Andrew Baumann <address@hidden>
> > ---
> >  include/hw/virtio/virtio.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> > index 15efcf2..a0a8543 100644
> > --- a/include/hw/virtio/virtio.h
> > +++ b/include/hw/virtio/virtio.h
> > @@ -34,7 +34,7 @@ struct VirtQueue;
> >  static inline hwaddr vring_align(hwaddr addr,
> >                                               unsigned long align)
> >  {
> > -    return (addr + align - 1) & ~(align - 1);
> > +    return (addr + align - 1) & ~(hwaddr)(align - 1);
> 
> Why not just use the QEMU_ALIGN_DOWN macro, instead of open-coding it?

Well, this code is aligning up, but yes the ALIGN_UP macro looks like it should 
also avoid the type promotion problem. This patch is just the 
minimally-invasive change after discovering the bug.

Let me know if you want me to spin another patch with the macro.

Andrew