[v2] Fix some GCC 9 build warnings

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

Posted by Alistair Francis 6 years, 6 months ago

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.
+ */
+#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);
-- 
2.21.0

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

Posted by Daniel P. Berrangé 6 years, 6 months ago

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

> +#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
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
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Re: [Qemu-devel] [PATCH v2 3/5] hw/usb/dev-mtp: Fix GCC 9 build warning

Posted by Alistair Francis 6 years, 6 months ago

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
> --
> |: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
> |: https://libvirt.org         -o-            https://fstop138.berrange.com :|
> |: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|

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

Posted by Thomas Huth 6 years, 6 months ago

On 01/05/2019 01.28, 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.
> + */
> +#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

Would it be possible to use an assert() instead? Something like

 g_assert((dataset->filename & 1) == 0)

?

 Thomas