Re: [Qemu-trivial] [Qemu-devel] [PATCH v1 3/5] hw/usb/dev-mtp: Fix GCC 9 build warning

[Alistair Francis]

On Tue, Apr 30, 2019 at 1:37 PM Eric Blake <address@hidden> wrote:
>
> On 4/30/19 3:09 PM, Alistair Francis wrote:
> > Fix this warning with GCC 9 on Fedora 30:
> > hw/usb/dev-mtp.c:1715:36: error: taking address of packed member of ‘struct 
> > <anonymous>’ may result in an unaligned pointer value 
> > [-Werror=address-of-packed-member]
> >  1715 |                             dataset->filename);
> >       |                             ~~~~~~~^~~~~~~~~~
> >
> > Signed-off-by: Alistair Francis <address@hidden>
> > ---
> >  hw/usb/dev-mtp.c | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> >
> > diff --git a/hw/usb/dev-mtp.c b/hw/usb/dev-mtp.c
> > index 99548b012d..6de85d99e6 100644
> > --- a/hw/usb/dev-mtp.c
> > +++ b/hw/usb/dev-mtp.c
> > @@ -1711,9 +1711,22 @@ static void usb_mtp_write_metadata(MTPState *s, 
> > uint64_t dlen)
> >      assert(!s->write_pending);
> >      assert(p != NULL);
> >
> > +/*
> > + * We are about to access a packed struct. We are confident that the 
> > pointer
> > + * address won't be unalligned, so we ignore GCC warnings.
>
> unaligned

Fixed.

>
> Aren't there other potential proposed patches floating around for this
> issue that do not involve messing with pragmas?

I'm not sure, I haven't seen anything. I'm more then open to a better
fix, this is the best option I could think of.

Alistair

>
> > + */
> > +#if defined(CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE) && QEMU_GNUC_PREREQ(9, 0)
> > +#pragma GCC diagnostic push
> > +#pragma GCC diagnostic ignored "-Waddress-of-packed-member"
> > +#endif
> > +
> >      filename = utf16_to_str(MIN(dataset->length, filename_chars),
> >                              dataset->filename);
> >
> > +#if defined(CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE) && QEMU_GNUC_PREREQ(9, 0)
> > +#pragma GCC diagnostic pop
> > +#endif
> > +
> >      if (strchr(filename, '/')) {
> >          usb_mtp_queue_result(s, RES_PARAMETER_NOT_SUPPORTED, d->trans,
> >                               0, 0, 0, 0);
> >
>
> --
> Eric Blake, Principal Software Engineer
> Red Hat, Inc.           +1-919-301-3226
> Virtualization:  qemu.org | libvirt.org
>