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[37.24.206.209]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-5c8e05eb34csm3927725a12.59.2024.10.07.22.59.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 07 Oct 2024 22:59:09 -0700 (PDT) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: 701a3ecd-853a-11ef-a0bc-8be0dac302b0 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=google; t=1728367150; x=1728971950; darn=lists.xenproject.org; h=in-reply-to:autocrypt:from:content-language:references:cc:to :subject:user-agent:mime-version:date:message-id:from:to:cc:subject :date:message-id:reply-to; bh=26d1rfUuMlhiGKmx+jD5HJ+W6LdLEy3kLIG52H3Zkcg=; b=RhQ5O4w2+WtVWTOZ7Jq+x5Nh6RugiYyOmquOLLsRVGEgk0JB7hyx25OZ+7ov8SFFtQ Jx1Xjs4Cu91yh01dcOTFuPwiiKYhhcEQJcmmi7F2P+R2qL50r+ElfbfagEO6GDc50hxn W2ns/V6/3F2/13jfBPQ4qTtt2UUf/Awdgn1JunhGKW5dRGoJwd92UQhAeMK/8dcIdrc3 Y/4QsAiAMh+GznXB0sYI8f4wS15nypSwCfEsLNcyVWNbOPxzaaZTwlYNshlfXPNrTUeF zuTl+eh3RiufGmVpPuQ4DvLY3JaEQpH7Xmmm+GvP6gZ/tHKPftO7ahbFkzBMcWloSBO3 SQQw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1728367150; x=1728971950; h=in-reply-to:autocrypt:from:content-language:references:cc:to :subject:user-agent:mime-version:date:message-id:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=26d1rfUuMlhiGKmx+jD5HJ+W6LdLEy3kLIG52H3Zkcg=; b=l3m9/tiXGS/Tnjt5dYOiXukzruELit0lMdmWmOXADUkyh+uWRvYpP6ARDGFpq3knLB /69EBxUDuWvSZBUDl3PFA550TBIwWP3uJJ/2sPITDoYUTuWbsq7a3ZVIzUcD4ImAIjIG pUNsWZOk6v6njVvGxGT7Pj8o3nzUF7i/KovItiWWRA7RyaG2AziJhD/Fi2F2o993zz+R ywKPEKhWZXnJhljqjOr/BNQwxgVVblSrm35BxKAiFM2IupQa6ieftjtw5upI6rkXzdef I0Mpy+x1PC//2jEbbVr0TWcPKNOgELRQT79vr72bseVv5Es18Z6g/cKAJA55gVMiwi/X 60fg== X-Forwarded-Encrypted: i=1; AJvYcCVsX5nSxVpyW/QtfBEHM4Hw+CNjSKC4Ar5b4kKuDAoHMd93AeFQahX4Ub5nbnwnScGCi5k9XFEjqzM=@lists.xenproject.org X-Gm-Message-State: AOJu0YxE2kI2bhISqOGr92i/5M9RwhqlaogAlgEyEr/ddaZh+C84uKiR xSRAWIGGc4wW/J009jMiw9b5iLjZ2ixVOPg0g5/a3FSY3csWKAZFAtHtsarL1g== X-Google-Smtp-Source: AGHT+IELPQp8jecRWkGRxxwA4EWYRUz9X79CLIDpxh6rGKDwJZ1Drp/Db9L6rlIYfTmX/96abZw1Wg== X-Received: by 2002:a5d:4411:0:b0:377:9867:9028 with SMTP id ffacd0b85a97d-37d0e8e2837mr8260587f8f.44.1728367150112; Mon, 07 Oct 2024 22:59:10 -0700 (PDT) Content-Type: multipart/mixed; boundary="------------2zBCrRS4K8n5HsxT4n0sMbJF" Message-ID: <1f8f6a0c-980f-43cb-9967-801641f8dbc0@suse.com> Date: Tue, 8 Oct 2024 07:59:08 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [XEN PATCH v2 1/3] EFI: address a violation of MISRA C Rule 13.6 To: Roberto Bagnara , Stefano Stabellini Cc: Federico Serafini , consulting@bugseng.com, "Daniel P. Smith" , =?UTF-8?Q?Marek_Marczykowski-G=C3=B3recki?= , Andrew Cooper , xen-devel@lists.xenproject.org References: <8d5e4761-9fc2-4e18-a6c2-9df1822dbbea@suse.com> <02833aad-d6f1-4ffa-8d4a-d8c31e9b0524@suse.com> <2f51a8e7-4044-4a84-a541-100799a28012@bugseng.com> Content-Language: en-US From: Jan Beulich Autocrypt: addr=jbeulich@suse.com; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL In-Reply-To: <2f51a8e7-4044-4a84-a541-100799a28012@bugseng.com> This is a multi-part message in MIME format. --------------2zBCrRS4K8n5HsxT4n0sMbJF Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 02.10.2024 08:54, Roberto Bagnara wrote: > On 2024-10-02 08:09, Jan Beulich wrote: >> On 01.10.2024 23:36, Stefano Stabellini wrote: >>> On Tue, 1 Oct 2024, Jan Beulich wrote: >>>> On 01.10.2024 07:25, Roberto Bagnara wrote: >>>>> On 2024-09-30 15:07, Jan Beulich wrote: >>>>>> On 30.09.2024 14:49, Federico Serafini wrote: >>>>>>> guest_handle_ok()'s expansion contains a sizeof() involving its >>>>>>> first argument which is guest_handle_cast(). >>>>>>> The expansion of the latter, in turn, contains a variable >>>>>>> initialization. >>>>>>> >>>>>>> Since MISRA considers the initialization (even of a local variable) >>>>>>> a side effect, the chain of expansions mentioned above violates >>>>>>> MISRA C:2012 Rule 13.6 (The operand of the `sizeof' operator shall not >>>>>>> contain any expression which has potential side effect). >>>>>> >>>>>> I'm afraid I need to ask for clarification of terminology and alike here. >>>>>> While the Misra doc has a section on Persistent Side Effects in its >>>>>> Glossary appendix, what constitutes a side effect from its pov isn't >>>>>> really spelled out anywhere. Which in turn raises the question whether it >>>>>> is indeed Misra (and not just Eclair) which deems initialization a side >>>>>> effect. This is even more so relevant as 13.6 talks of only expressions, >>>>>> yet initializers fall under declarations (in turn involving an expression >>>>>> on the rhs of the equal sign). >>>>>> >>>>>> All the same of course affects patch 2 then, too. >>>>> >>>>> MISRA C leaves the definition of "side effect" to the C Standard. >>>>> E.g., C18 5.1.2.3p2: >>>>> >>>>> Accessing a volatile object, modifying an object, modifying a file, >>>>> or calling a function that does any of those operations are all >>>>> side effects,[omitted irrelevant footnote reference] which are >>>>> changes in the state of the execution environment. >>>>> >>>>> The MISRA C:2012/2023 Glossary entry for "Persistent side effect" >>>>> indirectly confirms that initialization is always a side effect. >>>> >>>> Hmm, that's interesting: There's indeed an example with an initializer >>>> there. Yet to me the text you quote from the C standard does not say >>>> that initialization is a side effect - it would be "modifying an >>>> object" aiui, yet ahead of initialization being complete the object >>>> doesn't "exist" imo, and hence can be "modified" only afterwards. >>> >>> I feel it's becoming a bit too philosophical. Since there's some room >>> for interpretation and only two violations left to address, I believe >>> it's best to stick with the stricter interpretation of the definition. >>> Therefore, I'd proceed with this series in its current form. >> >> Proceeding with the series in its current form may be okay (as you say, >> you view the changes as readability improvements anyway), but imo the >> interpretation needs settling on no matter what. In fact even for these >> two patches it may affect what their descriptions ought to say (would >> be nice imo to avoid permanently recording potentially misleading >> information by committing as is). And of course clarity would help >> dealing with future instances that might appear. I take it you realize >> that if someone had submitted a patch adding code similar to the >> original forms of what's being altered here, it would be relatively >> unlikely for a reviewer to spot the issue. IOW here we're making >> ourselves heavily dependent upon Eclair spotting (supposed) issues, >> adding extra work and delays for such changes to go in. > > You can do two things to obtain a second opinion: > > 1) Use the MISRA forum (here is the link to the forum > section devoted to the side-effect rules of MISRA C:2012 > and MISRA C:2023 (https://forum.misra.org.uk/forumdisplay.php?fid=168). > The MISRA C Working Group will, in due course, provide > you with an official answer to your questions about what, > for the interpretation of Rule 13.6, has to be considered > a side effect. > > 2) Reach out to your ISO National Body and try to obtain > an official answer from ISO/IEC JTC1/SC22/WG14 (the > international standardization working group for the > programming language C) to your questions about what the > C Standard considers to be side effects. I took the latter route, and to my (positive) surprise I got back an answer the same day. There was a request for someone to confirm, but so far I didn't see further replies. Since this is a German institution I raised the question in German and got back an answer in German (attached); I've tried my best to translate this without falsifying anything, but I've omitted non-technical parts: "Initialization of an object is never a side effect of the initialization by itself. Of course expressions used for initialization can themselves have side effects on other objects. @Andreas: Do you agree? C after all has a far simpler object model than C++. The (potential) change in object representation (i.e. the bytes underlying the object) is not a side effect of object initialization, but its primary purpose." Further for Misra she added a reference to a Swiss person, but I think with Bugseng we have sufficient expertise there. 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Mein Hauptfokus liegt zwar auf C++, und C ist f=C3=BCr mich ein "Seiteneffe= kt", aber diese Frage kann ich vermutlich ebenfalls beantworten: Die Initialisierung eines Objekts ist niemals ein Seiteneffekt der Initiali= sierung von sich selbst. In den Expressions, welche zur Initialisierung eva= luiert werden, k=C3=B6nnen jedoch sehr wohl Seiteneffekte in anderen Objekt= en auftreten. @Andreas: kannst du dem zustimmen? C hat ja ein sehr viel einfacheres Objek= tmodell als C++. Die (potentielle) =C3=84nderung der Objektrepr=C3=A4sentat= ion (d.h. die Bytes, welche das Objekt hinterlegen) ist ja kein Seiteneffek= t der Objektinitialisierung, sondern sein prim=C3=A4rer Zweck. Wenn es um MISRA geht, w=C3=A4re sicherlich P. Sommerlad der richtige Anspr= echpartner (https://sommerlad.ch/). Ansonsten tagt das WG14 Komittee gerade= , gro=C3=9Fe Teile der WG14 Tafelrunde sind versammelt, Robert Seacord ist = sein Chair. lG Daniela > Wellh=C3=B6fer, Johannes hat am 02.10.2024 1= 5:02 CEST geschrieben: >=20 >=20 > Danke Manuela, f=C3=BCrs weiterleiten. > =20 > Sehr geehrter Herr Beulich,=20 > =20 > vielen Dank f=C3=BCr Ihre Anfrage. Ich habe Frau Engert hier mit in den = Emailverlauf genommen. Sie arbeitet als deutsche Expertin in der JTC1/SC22/= WG14 mit. >=20 > @Daniela Engert k=C3=B6nnen Sie Herrn Beulich mit seiner Frage (unten im = Verlauf gelb markiert) weiterhelfen? > =20 > Mit freundlichen Gr=C3=BC=C3=9Fen >=20 > Johannes Wellh=C3=B6fer > Er/Sein > Projektmanager > DIN-Normenausschuss Informationstechnik und Anwendungen (NIA) > DIN Deutsches Institut f=C3=BCr Normung e. V. =E2=80=93 Industrie und Inf= ormationstechnik (DIN =E2=80=93 NuS IIT IuA) >=20 > LinkedIn (https://www.linkedin.com/in/johannes-wellhoefer/) | T +49 30 26= 01-2455 | F +49 30 2601-4-2455 | M +49 174 2007820 > LinkedIn-Kanal des Normenausschusses f=C3=BCr Informationstechnik und Anw= endungen (https://www.linkedin.com/showcase/din-nia/) >=20 >=20 >=20 >=20 > Ab sofort kostenlos: Der Normungs-Monitor (https://www.din.de/de/din-und-= seine-partner/presse/mitteilungen/ab-januar-kostenlos-der-normungs-monitor-= 983794) > Unkompliziert zu Normungsprojekten Ihrer Branche auf dem Laufenden bleibe= n >=20 >=20 > Folgen Sie uns auf=09 https://twitter.com/DIN_Norm=09 https://www.linkedi= n.com/company/din-ev=09 https://www.youtube.com/user/DINBerlin=09 >=20 > DIN Deutsches Institut f=C3=BCr Normung e. V., Am DIN-Platz, Burggrafenst= ra=C3=9Fe 6, 10787 Berlin; www.din.de (http://www.din.de/)} Registergericht= : AG Berlin-Charlottenburg, VR 288 B; Pr=C3=A4sident: Ulrich B. Stoll; Vors= tand: Christoph Winterhalter (Vorsitzender), Daniel Schmidt; > Der Inhalt dieser E-Mail (einschlie=C3=9Flich Anh=C3=A4ngen) ist vertraul= ich. Falls Sie diese E-Mail versehentlich erhalten haben, l=C3=B6schen Sie = sie bitte und informieren den Absender. The contents of this e-mail (includ= ing attachments) are confidential. If you received this e-mail in error, pl= ease delete it and notify the sender. > -----Urspr=C3=BCngliche Nachricht----- > Von: Tillack-L=C3=BCbke, Manuela =20 > Gesendet: Mittwoch, 2. Oktober 2024 12:09 > An: Wellh=C3=B6fer, Johannes > Betreff: WG: Klarstellung zu ISO/IEC JTC1/SC22/WG14 >=20 > Lieber Johannes, >=20 > zust=C3=A4ndigkeitshalber bitte ich Dich um Beantwortung der unten angef= =C3=BCgten Anfrage. Vielen Dank. >=20 >=20 > Mit besten Gr=C3=BC=C3=9Fen >=20 > Manuela > AP A. 634 > -=C2=A02419 >=20 >=20 >=20 > -----Urspr=C3=BCngliche Nachricht----- > Von: info@din.de > Gesendet: Mittwoch, 2. Oktober 2024 10:17 > An: DIN Info > Betreff: Klarstellung zu ISO/IEC JTC1/SC22/WG14 >=20 > Guten Tag, >=20 > folgende Nachricht wurde auf https://www.din.de/de an Sie geschickt. >=20 > Guten Tag, >=20 > im Zusammenhang mit Misra C:2012 ist eine Interpretationsfrage zum C99 St= andard (ISO/IEC 9899:TC3) aufgetaucht. Zur Kl=C3=A4rung wurde ich an den IS= O National Body verwiesen, der - soweit ich feststellen kann - Sie sind. >=20 > Die eigentliche Frage betrifft "side effects": F=C3=A4llt die Initialisie= rung eines Objekts auch darunter? >=20 > In der Hoffnung, dass Sie uns bei der Kl=C3=A4rung behilflich sein k=C3= =B6nnen, m=C3=B6glicherweise auch durch Verweis an eine andere geeignete St= elle, vielen Dank im Voraus, > Jan Beulich >=20 > Herr Jan Beulich > jbeulich@suse.com --------------2zBCrRS4K8n5HsxT4n0sMbJF--