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v3 3/9] hw/usb: reorder fields in UASStatus To: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , qemu-devel@nongnu.org References: <20201105221905.1350-1-dbuono@linux.vnet.ibm.com> <20201105221905.1350-4-dbuono@linux.vnet.ibm.com> <4677dea1-bdd2-0095-e75c-2ca6d9be0cb9@redhat.com> From: Daniele Buono Message-ID: Date: Thu, 19 Nov 2020 11:16:52 -0500 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.4.1 MIME-Version: 1.0 In-Reply-To: <4677dea1-bdd2-0095-e75c-2ca6d9be0cb9@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.312, 18.0.737 definitions=2020-11-19_09:2020-11-19, 2020-11-19 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxlogscore=999 impostorscore=0 clxscore=1015 priorityscore=1501 bulkscore=0 adultscore=0 malwarescore=0 phishscore=0 suspectscore=2 lowpriorityscore=0 mlxscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2011190116 Received-SPF: none client-ip=148.163.158.5; envelope-from=dbuono@linux.vnet.ibm.com; helo=mx0a-001b2d01.pphosted.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/11/19 09:24:07 X-ACL-Warn: Detected OS = Linux 3.x [generic] X-Spam_score_int: -19 X-Spam_score: -2.0 X-Spam_bar: -- X-Spam_report: (-2.0 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_NONE=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Paolo Bonzini , Gerd Hoffmann Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Hi Philippe, On 11/6/2020 9:28 AM, Philippe Mathieu-Daudé wrote: > On 11/5/20 11:18 PM, Daniele Buono wrote: >> The UASStatus data structure has a variable sized field inside of type uas_iu, >> that however is not placed at the end of the data structure. >> >> This placement triggers a warning with clang 11, and while not a bug right now, >> (the status is never a uas_iu_command, which is the variable-sized case), >> it could become one in the future. > > The problem is uas_iu_command::add_cdb, indeed. > >> >> ../qemu-base/hw/usb/dev-uas.c:157:31: error: field 'status' with variable sized type 'uas_iu' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end] > > If possible remove the "../qemu-base/" as it does not provide > any useful information. > Sure, will do at the next cycle >> uas_iu status; >> ^ >> 1 error generated. >> >> Fix this by moving uas_iu at the end of the struct > > Your patch silents the warning, but the problem is the same. > It would be safer/cleaner to make 'status' a pointer on the heap IMO. I'm thinking of moving 'status' in a pointer with the following code changes: UASStatus is allocated in `usb_uas_alloc_status`, which currently does not take a type or size for the union field. I'm thinking of adding requested size for the status, like this: static UASStatus *usb_uas_alloc_status(UASDevice *uas, uint8_t id, uint16_t tag, size_t size); and the common call would be usb_uas_alloc_status([...],sizeof(uas_iu)); Also we'd need a double free when the object is freed. Right now it's handled in the code when the object is not used anymore with a `g_free(st);`. I'd have to replace it with `g_free(st->status); g_free(st);`. Would you suggest doing it place or by adding a usb_uas_dealloc_status() function? --- However, I am confused by the use of that variable-lenght field. I'm looking at what seems the only place where a command is parsed, in `usb_uas_handle_data`. uas_iu iu; [...] switch (p->ep->nr) { case UAS_PIPE_ID_COMMAND: length = MIN(sizeof(iu), p->iov.size); usb_packet_copy(p, &iu, length); [...] break; [...] It would seem that the copy is limited to at most sizeof(uas_iu), so even if we had anything in add_cdb[], that wouldn't be copied here? Is this intended? > >> >> Signed-off-by: Daniele Buono >> --- >> hw/usb/dev-uas.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/hw/usb/dev-uas.c b/hw/usb/dev-uas.c >> index cec071d96c..5ef3f4fec9 100644 >> --- a/hw/usb/dev-uas.c >> +++ b/hw/usb/dev-uas.c >> @@ -154,9 +154,9 @@ struct UASRequest { >> >> struct UASStatus { >> uint32_t stream; >> - uas_iu status; >> uint32_t length; >> QTAILQ_ENTRY(UASStatus) next; >> + uas_iu status; >> }; >> >> /* --------------------------------------------------------------------- */ >> >