Re: [Qemu-devel] [PATCH v2 3/5] hw/usb/dev-mtp: Fix GCC 9 build warning

[Alistair Francis <alistair23@gmail.com>]

On Wed, May 1, 2019 at 2:40 AM Daniel P. Berrangé <berrange@redhat.com> wrote:
>
> On Tue, Apr 30, 2019 at 11:28:41PM +0000, 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 <alistair.francis@wdc.com>
> > ---
> >  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..8233beacab 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 unaligned, so we ignore GCC warnings.
> > + */
>
> The data is mis-aligned as we're accessing an int16 array that
> is immediately following an int8 field in a packed struct
>
> This problem is fixed by the following series which Gerd has in the
> USB queue:
>
>   https://lists.gnu.org/archive/html/qemu-devel/2019-04/msg02524.html

Great, that fixes the build issues. Dropping this patch.

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);
>
> Regards,
> Daniel
> --
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