From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id 646B938A2851 for ; Thu, 31 Mar 2022 16:02:29 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 646B938A2851 Received: from mail-yw1-f200.google.com (mail-yw1-f200.google.com [209.85.128.200]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-338-tO8kC8tzNvuCjREeOt1KiQ-1; Thu, 31 Mar 2022 12:02:20 -0400 X-MC-Unique: tO8kC8tzNvuCjREeOt1KiQ-1 Received: by mail-yw1-f200.google.com with SMTP id 00721157ae682-2e5bcae3665so1877547b3.16 for ; Thu, 31 Mar 2022 09:02:20 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=7ePZRN1CBnM3+8R0l1epjIVnyddsemqnpb1MwqqA+xg=; b=uQlPsm4NZ31lTMo50MwHro91hm9YWEYLSUqfo1CT93M79ycog+8BcNhvmldbsveuGp PWI4QM+6mIyOcHl4+XzkBK5Zzg7KiShsqZlIpClpohMabKb0UMs88kUXdTsX68dDeFDr +xeaUX1aPKa3WlHUOuvBHzPtwdnX0gmh1ih4YSsicBq8ZF55K4NXKPStgkK0iZWy2ZMz 8JOwAMlFLLe4cE9kmtSl7H01wMDttl43CT7N2PosZvdy4V1XB93QGU1EHgjI94YvIYmU yq1zPTvZTGBt1a54f5FiF/8JPV+pIddi9xc6eo5eczQlipnGrZvK+D1dSr/sk3T4KABd 0lcw== X-Gm-Message-State: AOAM532tyw/g8uqSy4dC0hV4L38C2kflurpsQseYHWGbBdxDSpcB7brX h5NFo/QTdiX6upqA9eLCJsKP/k1cI/SaWFYXyu0jGyC8vqN7dYqHC/1snAP/RYxzFFl7GRf7gMn HIUgSwcuwn7zuSKO7tZpAvmpOKtFiPlQ= X-Received: by 2002:a05:690c:9:b0:2dd:1de0:7b13 with SMTP id bc9-20020a05690c000900b002dd1de07b13mr6059411ywb.450.1648742539528; Thu, 31 Mar 2022 09:02:19 -0700 (PDT) X-Google-Smtp-Source: ABdhPJw6mSLGQ6EHTfPTrLmy7lGd34JC11qtnCDzfivb6fcOiSi0YQS/LUN8xMgIfUIvbtJF1Zk7eDnloXkRXaDTxEQ= X-Received: by 2002:a05:690c:9:b0:2dd:1de0:7b13 with SMTP id bc9-20020a05690c000900b002dd1de07b13mr6059382ywb.450.1648742539271; Thu, 31 Mar 2022 09:02:19 -0700 (PDT) MIME-Version: 1.0 References: <20220331153029.1898244-1-jwakely@redhat.com> <3572914.e9J7NaK4W3@minbar> In-Reply-To: <3572914.e9J7NaK4W3@minbar> From: Jonathan Wakely Date: Thu, 31 Mar 2022 17:02:07 +0100 Message-ID: Subject: Re: [PATCH] libstdc++: Implement std::unreachable() for C++23 (P0627R6) To: Matthias Kretz Cc: gcc Patches , "libstdc++" X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-6.9 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H5, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_NONE, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: libstdc++@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libstdc++ mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 31 Mar 2022 16:02:31 -0000 On Thu, 31 Mar 2022 at 16:51, Matthias Kretz via Libstdc++ wrote: > > I like it. But I'd like it even more if we could have > > #elif defined _UBSAN > __ubsan_invoke_ub("reached std::unreachable()"); > > But to my knowledge UBSAN has no hooks for the library like this (yet). As far as I know, that's correct. > > +#ifdef _GLIBCXX_DEBUG > > + std::__glibcxx_assert_fail("", 0, "std::unreachable()", > > + "inconceivable!"); > > Funny message, but it should be more helpful, IMHO. :) We're currently limited to some string that can go inside "Assertion '...' failed." I also considered changing __glibcxx_assert_fail like so: --- a/libstdc++-v3/src/c++11/debug.cc +++ b/libstdc++-v3/src/c++11/debug.cc @@ -55,6 +55,8 @@ namespace std if (file && function && condition) fprintf(stderr, "%s:%d: %s: Assertion '%s' failed.\n", file, line, function, condition); + else if (function) + fprintf(stderr, "%s called.\n", function); abort(); } } And then making std::unreachable() call __glibcxx_assert_fail(0, 0, "std::unreachable()", 0).