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dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:53322 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kcOjK-0001K1-Kn for qemu-devel@archiver.kernel.org; Tue, 10 Nov 2020 03:10:18 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:34356) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kcOiL-0000FA-3c for qemu-devel@nongnu.org; Tue, 10 Nov 2020 03:09:17 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:20492) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kcOiH-00088m-Bz for qemu-devel@nongnu.org; Tue, 10 Nov 2020 03:09:16 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1604995752; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=BKjFpDPWgQCjCubiGVmQmUJLKfMpQKP+e0uqi4CbsGY=; b=fVB8B/XEZ2ENXuCShY8ZRPKjSfTCD2P/oCCMyY8hB9xgHbWspTzDpeCptSzG/0m4sYTYXP Sv8IsKJorcGqHpSCDK81QonoHkPCU1CTM2HxIz9DRzN/S9Of2CBgGdGmx3xf0ih4ngjZ34 d5EuDnxCfY9+E3pG2QqKHTs6GMQS4yE= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-172-zSn4UuCINZSRSddOrH3LiQ-1; Tue, 10 Nov 2020 03:09:08 -0500 X-MC-Unique: zSn4UuCINZSRSddOrH3LiQ-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 55BB7100830B; Tue, 10 Nov 2020 08:09:07 +0000 (UTC) Received: from thuth.remote.csb (ovpn-113-192.ams2.redhat.com [10.36.113.192]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2914910013BD; Tue, 10 Nov 2020 08:09:04 +0000 (UTC) Subject: Re: [PATCH] qtest: Fix bad printf format specifiers To: Markus Armbruster , Alex Chen 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> <877dqupudg.fsf@dusky.pond.sub.org> From: Thomas Huth Message-ID: <91546693-57fa-94f5-f42f-2c24eb994c33@redhat.com> Date: Tue, 10 Nov 2020 09:09:03 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <877dqupudg.fsf@dusky.pond.sub.org> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=thuth@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=thuth@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/11/10 00:21:06 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, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable 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: lvivier@redhat.com, QEMU Trivial , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , QEMU , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 09/11/2020 13.50, Markus Armbruster wrote: > Alex Chen writes: > >> On 2020/11/9 15:57, Markus Armbruster wrote: >>> Thomas Huth writes: >>> >>>> On 06/11/2020 15.18, Philippe Mathieu-Daudé 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 inttypes.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 continue 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 compilers >>>>>>> that we support. >>>>>> >>>>>> Yes, it works. >>>>>> >>>>>>> But if there is ever a compiler where the size of int 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 the >>>>>> type of the argument is actually uint32_t[1]. We can forget about this >>>>>> case, because "int narrower than 32 bits" is not going to fly with our >>>>>> code base. >>>> >>>> Agreed. >>>> >>>>>> If we ever use a compiler where int is wider than 32 bits, then the type >>>>>> of the argument is *not* uint32_t[2]. PRIu32 will work anyway, because >>>>>> 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 cases >>>> like this one here, where you multiply with an "int". But if you just try to >>>> print a plain uint32_t variable? >>> >>> Default argument promotions (§6.5.2.2 Function calls) still apply: "the >>> integer promotions are performed on each argument, and arguments that >>> have type float are promoted to double." >>> >>>> I've seen compiler warning in cases one tries to print a 16-bit (i.e. short) >>>> 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 architectures. >>>> If you're statement was right, that should not have happened, should it? >>> >>> §7.19.6.1 "The fprintf function" on length modifier 'h': >>> >>> 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) >>> >>> 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. >>> >>> However, printing an int with %hd has: it converts int to short. >>> Implementation-defined behavior when the value doesn't fit. >>> >>> Length modifier 'h' is pretty pointless with printf(). So would be a >>> warning to nudge people towards its use. >>> >>> In fact, GNU libc's PRIu32 does not use it. inttypes.h: >>> >>> /* Unsigned integers. */ >>> # define PRIu8 "u" >>> # define PRIu16 "u" >>> # define PRIu32 "u" >>> # define PRIu64 __PRI64_PREFIX "u" >>> >>> where __PRI64_PREFIX is "l" or "ll" depending on system-dependent >>> __WORDSIZE. >>> >>> In short: >>> >>>>>> In other words "%" PRIu32 is just a less legible alias for "%u" in all >>>>>> cases that matter. >>> >> >> 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. Just FYI, there are also apparently toolchains where uint32_t is defined as unsigned long: https://patchwork.kernel.org/project/kvm/patch/20201105135936.55088-1-alexandru.elisei@arm.com/ Thomas