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

[Laurent Vivier]

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 <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.
>> + */
>> +#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