220 38128 article Path: news.gmane.org!.POSTED!not-for-mail From: "dgutson ." Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: memcpy/memset/etc overloads for volatile memory Date: Fri, 18 May 2018 17:53:14 -0300 Lines: 162 Approved: news@gmane.org Message-ID: References: <0e5ce74c-3e9e-4cf2-4afd-f7333ed82c5d@gmail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="00000000000008e487056c8124da" X-Trace: blaine.gmane.org 1526676669 31721 195.159.176.226 (18 May 2018 20:51:09 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 18 May 2018 20:51:09 +0000 (UTC) To: std-proposals Original-X-From: std-proposals+bncBDE3NBMV6UFBBO727TLQKGQEJLUJZIQ@isocpp.org Fri May 18 22:51:05 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qk0-f200.google.com ([209.85.220.200]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1fJmLA-0008Aw-Tt for gclcip-std-proposals@m.gmane.org; Fri, 18 May 2018 22:51:05 +0200 Original-Received: by mail-qk0-f200.google.com with SMTP id c8-v6sf7960576qkb.21 for ; 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[209.85.220.41]) by mx.google.com with SMTPS id v124-v6sor6608529qka.1.2018.05.18.13.53.15 for (Google Transport Security); Fri, 18 May 2018 13:53:15 -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:a37:a1cb:: with SMTP id k194-v6mr3997549qke.330.1526676794694; Fri, 18 May 2018 13:53:14 -0700 (PDT) Original-Received: by 10.12.172.172 with HTTP; Fri, 18 May 2018 13:53:14 -0700 (PDT) In-Reply-To: <0e5ce74c-3e9e-4cf2-4afd-f7333ed82c5d@gmail.com> X-Original-Sender: danielgutson@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=LqAhcaHc; 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:38128 Archived-At: --00000000000008e487056c8124da Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Fri, May 18, 2018 at 5:46 PM, Andrey Semashev wrote: > On 05/18/18 23:41, dgutson . wrote: > >> This might be interesting. >> >> In some systems, the implementation of memcpy() & friends cannot be used >> for memory-mapped devices. >> Usually, mapped memory is marked as volatile. >> >> I'm proposing to add volatile pointers overloads for the memcpy() >> function and friends, without specifying exactly what should be differen= t >> at the standard-level, but allowing implementations to provide a particu= lar >> behavior. I'm just proposing to add the declaration to the standard. >> >> Particularly, in some x86-based systems, reading things like the SPI >> should be done on byte-per-byte basis (rather than streamed with any SIM= D >> instruction). >> >> I'm not sure what the wording should exactly say, but I'm just initiatin= g >> the discussion. >> > > If it's not specified then the exact behavior wrt. memory accesses is not > going to be portable, which means it's not going to be useful. It is useful indeed: if I have a pointer to volatile memory, I cannot use memcpy currently. By adding the overload, I'm being guaranteed that I will be able to call memcpy (and that the implementation shall DTRT, which is for example, the byte per byte copying). Besides the "DTRT" discussion, my point is: I want this overload to be available. At least it should fall back to the non-volatile version. > > > -- > 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/is > ocpp.org/d/msgid/std-proposals/0e5ce74c-3e9e-4cf2-4afd- > f7333ed82c5d%40gmail.com. > --=20 Who=E2=80=99s got the sweetest disposition? One guess, that=E2=80=99s who? Who=E2=80=99d never, ever start an argument? Who never shows a bit of temperament? Who's never wrong but always right? Who'd never dream of starting a fight? Who get stuck with all the bad luck? --=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-3V0VJ9nOs2fg4OuRr4N8TG-VXsrek1v%3DCJpr%3D= Bqt98%2BQ%40mail.gmail.com. --00000000000008e487056c8124da Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable


On Fri, May 18, 2018 at 5:46 PM, Andrey Semashev <= andrey.semas= hev@gmail.com> wrote:
On 05/18/18 23:41, dgutson . wrote:
This might be interesting.

In some systems, the implementation of memcpy() & friends cannot be use= d for memory-mapped devices.
Usually, mapped memory is marked as volatile.

I'm proposing to add volatile pointers overloads for the memcpy() funct= ion and friends, without specifying exactly what should be different at the= standard-level, but allowing implementations to provide a particular behav= ior. I'm just proposing to add the declaration to the standard.

Particularly, in some x86-based systems, reading things like the SPI should= be done on byte-per-byte basis (rather than streamed with any SIMD instruc= tion).

I'm not sure what the wording should exactly say, but I'm just init= iating the discussion.

If it's not specified then the exact behavior wrt. memory accesses is n= ot going to be portable, which means it's not going to be useful.

It is useful indeed: if I have a pointer to vola= tile memory, I cannot use memcpy currently.
By adding the overloa= d, I'm being guaranteed that I will be able to call memcpy (and that th= e implementation shall DTRT, which is for example, the byte per byte copyin= g).
Besides the "DTRT" discussion, my point is: I want = this overload to be available. At least it should fall back to the non-vola= tile version.
=C2=A0


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--
Who=E2= =80=99s got the sweetest disposition?
One guess, that=E2=80=99s who?
= Who=E2=80=99d never, ever start an argument?
Who never shows a bit of te= mperament?
Who's never wrong but always right?
Who'd never dr= eam of starting a fight?
Who get stuck with all the bad luck?

--
You received this message because you are subscribed to the Google Groups &= quot;ISO C++ Standard - Future Proposals" group.
To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposa= ls+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-3V0V= J9nOs2fg4OuRr4N8TG-VXsrek1v%3DCJpr%3DBqt98%2BQ%40mail.gmail.com.
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