220 40244 article Path: news.gmane.org!.POSTED!not-for-mail From: Daniel Gutson Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: more security concerns Date: Fri, 28 Sep 2018 11:17:56 -0300 Lines: 274 Approved: news@gmane.org Message-ID: References: <94d79dd7-ba3b-4bf8-91ed-e5dc02b33670@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="000000000000ffc75a0576ef1f3f" X-Trace: blaine.gmane.org 1538144166 19285 195.159.176.226 (28 Sep 2018 14:16:06 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 28 Sep 2018 14:16:06 +0000 (UTC) To: std-proposals Original-X-From: std-proposals+bncBDE3NBMV6UFBBI7QXDOQKGQEXASPTDY@isocpp.org Fri Sep 28 16:16:02 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lj1-f200.google.com ([209.85.208.200]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1g5tYn-0004tH-2x for gclcip-std-proposals@m.gmane.org; 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[209.85.220.41]) by mx.google.com with SMTPS id h3-v6sor3318506ljg.13.2018.09.28.07.18.10 for (Google Transport Security); Fri, 28 Sep 2018 07:18:10 -0700 (PDT) Received-SPF: pass (google.com: domain of danielgutson@gmail.com designates 209.85.220.41 as permitted sender) client-ip=209.85.220.41; X-Received: by 2002:a2e:9a93:: with SMTP id p19-v6mr9203lji.87.1538144289669; Fri, 28 Sep 2018 07:18:09 -0700 (PDT) In-Reply-To: <94d79dd7-ba3b-4bf8-91ed-e5dc02b33670@isocpp.org> X-Original-Sender: danielgutson@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=Zle45bT2; spf=pass (google.com: domain of danielgutson@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=danielgutson@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Spam-Checked-In-Group: std-proposals@isocpp.org X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:40244 Archived-At: --000000000000ffc75a0576ef1f3f Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable El vie., 28 sept. 2018 11:14, escribi=C3=B3: > I want to highlight that [[nodiscard]] on functions is not about forcing > the compiler to keep the value, but instead to emit a warning if the user > doesn't use the value. > I'm proposing using [[nodiscard]] for statements rather than for declarations. That being said, it would be placed in the function call statement. I want the compiler to still do DSE where appropriate and at the same time allow the programmer to thoughtfully prevent it. So meaning would be different. > In that respect, another attribute name might be better. > > Also, it is already possible (but cumbersome) to implement already withou= t > volatile: > void f() { > int secret_int; > float secret_float; > /* ... */ > secret_int =3D 0; > secret_float =3D 0 > asm volatile ("" ::"irm"(secret_int), "xm"(secret_float)); > } > > I would really like an attribute for that, though. > > > Le vendredi 28 septembre 2018 15:36:42 UTC+2, Daniel Gutson a =C3=A9crit = : >> >> Yeah. But please note that this is not only for function calls. >> >> void f() >> { >> int secret; >> .... >> secret =3D 0; //removed due to DSE >> } >> >> If I declare secret as volatile or write 0s to its address I may prevent >> the compiler to use a register impacting in performance. That's why I wa= nt >> to use the attribute here too. >> >> >> >> El vie., 28 sept. 2018 10:32, Andrew Giese escribi= =C3=B3: >> >>> I like the idea. >>> Function poisoning might also serve your needs. E.g., >>> https://www.fluentcpp.com/2018/09/04/function-poisoning-in-cpp/ >>> >>> If gcc poison were standardized in some fashion, you could write your >>> own wrappers to those functions with all the [[nodiscard]] you might wa= nt. >>> >>> Control in that case is a little less granular, indeed. Probably if >>> you're writing [[nodiscard]] on a per-expression basis you are not >>> discarding the result already. >>> >>> Regards >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "ISO C++ Standard - Future Proposals" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to std-proposal...@isocpp.org. >>> To post to this group, send email to std-pr...@isocpp.org. >>> To view this discussion on the web visit >>> https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/CAO8_tC4kN= Z6s-xMXo69n1D3dbOMkqt0fjLU44Uq5TfABp17hQQ%40mail.gmail.com >>> >>> . >>> >> -- > You received this message because you are subscribed to the Google Groups > "ISO C++ Standard - Future Proposals" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to std-proposals+unsubscribe@isocpp.org. > To post to this group, send email to std-proposals@isocpp.org. > To view this discussion on the web visit > https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/94d79dd7-ba3= b-4bf8-91ed-e5dc02b33670%40isocpp.org > > . > --=20 You received this message because you are subscribed to the Google Groups "= ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. To view this discussion on the web visit https://groups.google.com/a/isocpp= ..org/d/msgid/std-proposals/CAFdMc-1tpJj3bSzHgD%3DpxWD2eVokRX3ST2QE-oF6M8z1%= 3DDTEoQ%40mail.gmail.com. --000000000000ffc75a0576ef1f3f Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable


= El vie., 28 sept. 2018 11:14, <florian.csdt@gmail.com> escribi=C3=B3:
I want to highlight that [[nodiscard]] on fu= nctions is not about forcing the compiler to keep the value, but instead to= emit a warning if the user doesn't use the value.

I'm proposi= ng using [[nodiscard]] for statements rather than for declarations.
That being said, it would be placed in the function call st= atement. I want the compiler to still do DSE where appropriate and at the s= ame time allow the programmer to thoughtfully prevent it.


So meaning wo= uld be different.
In that respect, another attribute name might be bette= r.

Also, it is already possible (but cumbersome) to implement alread= y without volatile:
void f() {
=C2=A0 int secret_int;
=C2=A0 float secret= _float;
=C2=A0 /* ... */
=C2=A0 s= ecret_int =3D 0;
=C2=A0 sec= ret_float =3D 0
=C2=A0 asm<= /span> volatile (""<= span style=3D"color:#000" class=3D"m_1356521278005008546styled-by-prettify"= > ::"irm"(secret_int= ), "xm"(secret_float<= span style=3D"color:#660" class=3D"m_1356521278005008546styled-by-prettify"= >));
}

I wou= ld really like an attribute for that, though.


Le vendredi 28 sep= tembre 2018 15:36:42 UTC+2, Daniel Gutson a =C3=A9crit=C2=A0:
Yeah.=C2=A0 But please not= e that this is not only for function calls.

void f()
{
=C2= =A0 =C2=A0int secret;
=C2=A0 =C2=A0....
=C2=A0 =C2=A0secret =3D 0;=C2=A0 //removed due to DSE
}

If I decl= are secret as volatile or write 0s to its address I may prevent the compile= r to use a register impacting in performance. That's why I want to use = the attribute here too.



El vie., 28 sept. 2018 10:32, Andrew Gies= e <gies...@gmail.com> escribi=C3= =B3:
I like = the idea.
Function poisoning might also serve your needs. = E.g.,=C2=A0https://www.fluen= tcpp.com/2018/09/04/function-poisoning-in-cpp/
<= br>
If gcc poison were standardized in some fashion,= you could write your own wrappers to those functions with all the [[nodisc= ard]] you might want.

Co= ntrol in that case is a little less granular, indeed. Probably if you'r= e writing [[nodiscard]] on a per-expression basis you are not discarding th= e result already.

Regard= s

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