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

Alistair Francis posted 5 patches 6 years, 6 months ago
There is a newer version of this series
[Qemu-devel] [PATCH v1 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..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.
+ */
+#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 v1 3/5] hw/usb/dev-mtp: Fix GCC 9 build warning
Posted by Laurent Vivier 6 years, 6 months ago 
Le 30/04/2019 à 22:09, Alistair Francis a écrit :
> 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..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.
> + */
> +#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);
> 

You should move and use PRAGMA_DISABLE_PACKED_WARNING and
PRAGMA_REENABLE_PACKED_WARNING from linux-user/qemu.h.

It has laready been very well tested :)

Thanks,
Laurent
Re: [Qemu-devel] [PATCH v1 3/5] hw/usb/dev-mtp: Fix GCC 9 build warning
Posted by Laurent Vivier 6 years, 6 months ago 
Le 30/04/2019 à 22:28, Laurent Vivier a écrit :
> Le 30/04/2019 à 22:09, Alistair Francis a écrit :
>> 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..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.
>> + */
>> +#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);
>>
> 
> You should move and use PRAGMA_DISABLE_PACKED_WARNING and
> PRAGMA_REENABLE_PACKED_WARNING from linux-user/qemu.h.
> 
> It has laready been very well tested :)


Oh, they are for clang and a false positive, so forget my comment (and
the following one)

Thanks,
Laurent
Re: [Qemu-devel] [PATCH v1 3/5] hw/usb/dev-mtp: Fix GCC 9 build warning
Posted by Eric Blake 6 years, 6 months ago 
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 <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..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

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

> + */
> +#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
Re: [Qemu-devel] [PATCH v1 3/5] hw/usb/dev-mtp: Fix GCC 9 build warning
Posted by Alistair Francis 6 years, 6 months ago 
On Tue, Apr 30, 2019 at 1:37 PM Eric Blake <eblake@redhat.com> 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 <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..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
>

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