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 [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id C287D389942E for ; Thu, 31 Mar 2022 16:02:29 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org C287D389942E Received: from mail-yw1-f197.google.com (mail-yw1-f197.google.com [209.85.128.197]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-441-n0PtoOzXOt-_hMnwBiZwpQ-1; Thu, 31 Mar 2022 12:02:22 -0400 X-MC-Unique: n0PtoOzXOt-_hMnwBiZwpQ-1 Received: by mail-yw1-f197.google.com with SMTP id 00721157ae682-2e5a3c1384cso2244707b3.4 for ; Thu, 31 Mar 2022 09:02:21 -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=i8q8V5wfQ/d4WwaRkMZvje2+vZOL2aGJJh7F4jq5UC2V6yfdUwne7xSiod65zf9+jq bwKAPgqU1BUOHIp32qP7m42q9Xj6NjyuLcT1df5B6JDlnXLqmF/cXLSVTUIDvCxFU7IZ BEsomYc9O+6orKxB7n6sGz0QTiTRWCgjS9u0WBFV1QroYCKEbR6JdJQqmmvQgdU5Jx+S ZXmUa7/H/lpyXlj79hHjXHH0jhBd57DEkV6CRw5Zs8mNgAM08U/2uLeskLCocgWkWVBB GNL7yqvy4L+FP66SElXYjvDTNkXlj8nl7Mu3YG/BxFHS6u+1oUNsPBdofCDH0IyPbPZ7 yibg== X-Gm-Message-State: AOAM5314czHuL6lzytyG1IUc/gd45f1Uzq2i/bIkYFpaCgteRAsq1hXQ kZphXSgt7eT+GmM2punnjUwzPOEAmuChMg4kByaswTwl2Olj1x4uVAT0saiFSAvoJO91XYqmIDy 2NJkowvZGIWXgrslLIrAStZTQrYodd/KE0Q== X-Received: by 2002:a05:690c:9:b0:2dd:1de0:7b13 with SMTP id bc9-20020a05690c000900b002dd1de07b13mr6059413ywb.450.1648742539529; 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=-4.2 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_H4, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_NONE, TXREP, T_SCC_BODY_TEXT_LINE autolearn=unavailable autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches 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).