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Mon, 9 Nov 2020 13:50:03 +0100 (CET) From: Markus Armbruster To: Alex Chen Cc: lvivier@redhat.com, Thomas Huth , QEMU Trivial , QEMU , Paolo Bonzini , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Subject: Re: [PATCH] qtest: Fix bad printf format specifiers References: <5FA28117.3020802@huawei.com> <67eca43e-99ea-f2ce-5d9e-a9cb5c7a3a83@redhat.com> <5FA38A32.2020008@huawei.com> <18690aa2-3de9-70ad-477f-934724b284a0@redhat.com> <87wnyzouy4.fsf@dusky.pond.sub.org> <1fd5965d-cf5e-b41b-2029-bd3e52c3e498@redhat.com> <8f5ef0b8-4c43-034f-f609-e7e5ca013970@redhat.com> <87d00narns.fsf@dusky.pond.sub.org> <5FA91234.1010708@huawei.com> Date: Mon, 09 Nov 2020 13:50:03 +0100 In-Reply-To: <5FA91234.1010708@huawei.com> (Alex Chen's message of "Mon, 9 Nov 2020 17:56:04 +0800") Message-ID: <877dqupudg.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=216.205.24.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/11/09 00:04:29 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-trivial@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 09 Nov 2020 12:50:13 -0000 Alex Chen writes: > On 2020/11/9 15:57, Markus Armbruster wrote: >> Thomas Huth writes: >>=20 >>> On 06/11/2020 15.18, Philippe Mathieu-Daud=C3=A9 wrote: >>>> On 11/6/20 7:33 AM, Markus Armbruster wrote: >>>>> Thomas Huth writes: >>>>> >>>>>> On 05/11/2020 06.14, AlexChen wrote: >>>>>>> On 2020/11/4 18:44, Thomas Huth wrote: >>>>>>>> On 04/11/2020 11.23, AlexChen wrote: >>>>>>>>> We should use printf format specifier "%u" instead of "%d" for >>>>>>>>> argument of type "unsigned int". >>>>>>>>> >>>>>>>>> Reported-by: Euler Robot >>>>>>>>> Signed-off-by: Alex Chen >>>>>>>>> --- >>>>>>>>> tests/qtest/arm-cpu-features.c | 8 ++++---- >>>>>>>>> 1 file changed, 4 insertions(+), 4 deletions(-) >>>>>>>>> > [...] >>>>>>>>> >>>>>>>> >>>>>>>> max_vq and vq are both "uint32_t" and not "unsigned int" ... so if= you want >>>>>>>> to fix this really really correctly, please use PRIu32 from inttyp= es.h instead. >>>>>>>> >>>>>>> >>>>>>> Hi Thomas, >>>>>>> Thanks for your review. >>>>>>> According to the definition of the macro PRIu32(# define PRIu32 = "u"), >>>>>>> using PRIu32 works the same as using %u to print, and using PRIu32 = to print >>>>>>> is relatively rare in QEMU(%u 720, PRIu32 only 120). Can we continu= e to use %u to >>>>>>> print max_vq and vq in this patch. >>>>>>> Of course, this is just my small small suggestion. If you think it = is better to use >>>>>>> PRIu32 for printing, I will send patch V2. >>>>>> >>>>>> Well, %u happens to work since "int" is 32-bit with all current comp= ilers >>>>>> that we support. >>>>> >>>>> Yes, it works. >>>>> >>>>>> But if there is ever a compiler where the size of i= nt is >>>>>> different, you'll get a compiler warning here again. >>>>> >>>>> No, we won't. >>>>> >>>>> If we ever use a compiler where int is narrower than 32 bits, then th= e >>>>> type of the argument is actually uint32_t[1]. We can forget about th= is >>>>> case, because "int narrower than 32 bits" is not going to fly with ou= r >>>>> code base. >>> >>> Agreed. >>> >>>>> If we ever use a compiler where int is wider than 32 bits, then the t= ype >>>>> of the argument is *not* uint32_t[2]. PRIu32 will work anyway, becau= se >>>>> it will actually retrieve an unsigned int argument, *not* an uint32_t >>>>> argument[3]. >>> >>> I can hardly believe that this can be true. Sure, it's true for such ca= ses >>> like this one here, where you multiply with an "int". But if you just t= ry to >>> print a plain uint32_t variable? >>=20 >> Default argument promotions (=C2=A76.5.2.2 Function calls) still apply: = "the >> integer promotions are performed on each argument, and arguments that >> have type float are promoted to double." >>=20 >>> I've seen compiler warning in cases one tries to print a 16-bit (i.e. s= hort) >>> variable in the past if you use %d instead of the proper PRId16 (or %hd= ) >>> format specifier - maybe not on x86, but certainly on other architectur= es. >>> If you're statement was right, that should not have happened, should it= ? >>=20 >> =C2=A77.19.6.1 "The fprintf function" on length modifier 'h': >>=20 >> Specifies that a following d, i, o, u, x, or X conversion specifier >> applies to a short int or unsigned short int argument (the argument >> will have been promoted according to the integer promotions, but its >> value shall be converted to short int or unsigned short int before >> printing) >>=20 >> Integer promotions preserve value including sign. So, printing a short >> value with %hd first promotes it to int, then converts it back to short. >> Neither conversion has an effect. >>=20 >> However, printing an int with %hd has: it converts int to short. >> Implementation-defined behavior when the value doesn't fit. >>=20 >> Length modifier 'h' is pretty pointless with printf(). So would be a >> warning to nudge people towards its use. >>=20 >> In fact, GNU libc's PRIu32 does not use it. inttypes.h: >>=20 >> /* Unsigned integers. */ >> # define PRIu8=09=09"u" >> # define PRIu16=09=09"u" >> # define PRIu32=09=09"u" >> # define PRIu64=09=09__PRI64_PREFIX "u" >>=20 >> where __PRI64_PREFIX is "l" or "ll" depending on system-dependent >> __WORDSIZE. >>=20 >> In short: >>=20 >>>>> In other words "%" PRIu32 is just a less legible alias for "%u" in al= l >>>>> cases that matter. >>=20 > > Hi Markus, > > Thanks for your reply, I have learned a lot. > May I understand it as follows: > %u is used when there are parameters obtained by arithmetic operation; > otherwise, PRIu32 is used to print uint32_t type parameters? No. Use "%u" unless you need portability to machines where unsigned is narrower than 32 bits (we don't). On machines where unsigned int is at least 32 bit wide, "%" PRIu32 is the same as "%u". It's not wrong, just illegible.