From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm1-x32b.google.com (mail-wm1-x32b.google.com [IPv6:2a00:1450:4864:20::32b]) by sourceware.org (Postfix) with ESMTPS id 2FAD83858D1E; Sun, 12 Nov 2023 01:33:58 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 2FAD83858D1E Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=gmail.com ARC-Filter: OpenARC Filter v1.0.0 sourceware.org 2FAD83858D1E Authentication-Results: server2.sourceware.org; arc=none smtp.remote-ip=2a00:1450:4864:20::32b ARC-Seal: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1699752840; cv=none; b=mOKzMJW+CE+gVl1z6SBKAwKPVQg1CUPiA7v5PykUpSaWHfuxpCJZTOQH7/9ybjLp4yH7HAEPtS0b1zratO0ht2BMjedROtbOmnBs+nTAu0Kv1sBucHXDJKWyiLQFPwCmq6JANksCdKXnHh9AXTeiEG6njDXN4HlvjB7zHs1WpSQ= ARC-Message-Signature: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1699752840; c=relaxed/simple; bh=tYkiNCLOSI3CLra6E5knbHDXqm6CL18yUk3Uuas6Qqw=; h=DKIM-Signature:From:To:Subject:Date:Message-ID:MIME-Version; b=MuMPDu9nzcbgwnWlzDCtSGxfq4u9S2Ai3Ox/vxTGZOHZjwKa8blzVuZ74JjMHYmCo9lXB0pQ46HvMnhsb/lTW1/li93Hg/zRsXyOmc5bqxJftIRKXdhvxx8O1CEaG20agOZ5iCkWGy5hKO1BuWKtgSW7F/DxxKyqpWtdU3zsRGI= ARC-Authentication-Results: i=1; server2.sourceware.org Received: by mail-wm1-x32b.google.com with SMTP id 5b1f17b1804b1-40806e4106dso18958335e9.1; Sat, 11 Nov 2023 17:33:58 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1699752836; x=1700357636; darn=gcc.gnu.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=ddpxPjTYqMpFZvEYdfy6YQUya76v1wU9i4VkCYV2WEo=; b=OHCo/Y2bzJwGarqvXAbj+hWmWWnnrlP+3BN3tkiRI18ytNLyAF/TTXT6RSBx7ZKONp ogerO43qZJIeltIdpx1LDweUg2EVXXL55EMpeCOydNWpmBUgU/1/xTByN4PcrmcaSu9q SH8spqjNexYjOJA3iBnjYsBUOhkuhVHiI4c9uPrWonFpqxjyQzSQhA/FqIcHNsgHdu6u BtZXftzbRyRqrMnQ5KCrcWDyxh/sHo+dMZdCVsdBE644fFKx+89tywzyoRYgSJLFBNM1 LlzT02sty7gC2jtX+XuGbwkkTUX2PPnS28gX+G20JQ0qRAE+3R22D5PN3wExhzaCtF9Q kkvQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1699752836; x=1700357636; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=ddpxPjTYqMpFZvEYdfy6YQUya76v1wU9i4VkCYV2WEo=; b=VbscbuqeIBUhzVjePy/PDdPIr7jyS9b67PGmnNT0ljZpkGbCscr+fA1AROy3Ty0w4K 2DlHJaefL6LiICSCG6Qm+UZQzUJPOhv/3PnoDy05IxqFSB1Ejgs28bSCa9K9cw4q0Zae SKcNj2S9jgXaHvW9ywlCZPhIpfxISoysumKE0DWXIRfWVaVKumuGJtA2qDgjURsDi+LP Rnlk0aPtzqQ6t/o7QbFKk2qkMFyLRFsEZ04h5RX3o1gs7mvK33oH47qGxxqmAIkRXqJN c+iYl0W6HHpLiEZDzoORBOqD1m07NXUWe49TwpTO1NRkSX5MdCizZJjInTXznJeln8ET ImLg== X-Gm-Message-State: AOJu0Ywd/vzy+W42AR2+Ayayk/fceacU9C9vgKIvRic7EGJ+rpsiwZLI +q0q/SFWMkaQJqxSEKK5+lqzyMWMeQI= X-Google-Smtp-Source: AGHT+IFyHrOjrKnsIDZlSVRoR7bSHCLHf0TBl3sQIlXXPlI9Ua/vnDERbjL3i7JzG3bOR7nIvfZeRw== X-Received: by 2002:a05:600c:3c8b:b0:409:6e0e:e95a with SMTP id bg11-20020a05600c3c8b00b004096e0ee95amr2487002wmb.19.1699752836038; Sat, 11 Nov 2023 17:33:56 -0800 (PST) Received: from othello.cust.communityfibre.co.uk ([2a02:6b64:8086:0:f9dd:28dd:c9b9:d8f4]) by smtp.gmail.com with ESMTPSA id p37-20020a05600c1da500b004064ac107cfsm3615664wms.39.2023.11.11.17.33.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 11 Nov 2023 17:33:55 -0800 (PST) From: Cassio Neri To: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org Cc: Cassio Neri Subject: [PATCH] Fix UB in weekday::weekday(sys_days) and add test. Date: Sun, 12 Nov 2023 01:33:52 +0000 Message-ID: <20231112013352.19885-1-cassio.neri@gmail.com> X-Mailer: git-send-email 2.41.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-11.9 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM,GIT_PATCH_0,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: The following has undefined behaviour (signed overflow) [1]: weekday max{sys_days{days{numeric_limits::max()}}}; The issue is in this line when __n is very large and __n + 4 overflows: return weekday(__n >= -4 ? (__n + 4) % 7 : (__n + 5) % 7 + 6); In addition to fixing this bug, the new implementation makes the compiler emit shorter and branchless code for x86-64 and ARM [2]. [1] https://godbolt.org/z/1s5bv7KfT [2] https://godbolt.org/z/zKsabzrhs libstdc++-v3/ChangeLog: * include/std/chrono: Fix weekday::_S_from_days * testsuite/std/time/weekday/1.cc: Add test for overflow. --- Good for trunk? libstdc++-v3/include/std/chrono | 11 +++++++++-- libstdc++-v3/testsuite/std/time/weekday/1.cc | 9 +++++++++ 2 files changed, 18 insertions(+), 2 deletions(-) diff --git a/libstdc++-v3/include/std/chrono b/libstdc++-v3/include/std/chrono index 10e868e5a03..c00dd133173 100644 --- a/libstdc++-v3/include/std/chrono +++ b/libstdc++-v3/include/std/chrono @@ -930,8 +930,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION static constexpr weekday _S_from_days(const days& __d) { - auto __n = __d.count(); - return weekday(__n >= -4 ? (__n + 4) % 7 : (__n + 5) % 7 + 6); + using _Rep = days::rep; + using _URep = make_unsigned_t<_Rep>; + const auto __n = __d.count(); + const auto __m = static_cast<_URep>(__n); + + // 1970-01-01 (__n = 0, __m = 0 ) -> Thursday (4) + // 1969-31-12 (__n = -1, __m = _URep(-1)) -> Wednesday (3) + const auto __offset = __n >= 0 ? _URep(4) : 3 - _URep(-1) % 7 - 7; + return weekday((__m + __offset) % 7); } public: diff --git a/libstdc++-v3/testsuite/std/time/weekday/1.cc b/libstdc++-v3/testsuite/std/time/weekday/1.cc index 00278c8b01c..e89fca47d4b 100644 --- a/libstdc++-v3/testsuite/std/time/weekday/1.cc +++ b/libstdc++-v3/testsuite/std/time/weekday/1.cc @@ -20,6 +20,7 @@ // Class template day [time.cal.weekday] #include +#include constexpr void constexpr_weekday() @@ -37,6 +38,14 @@ constexpr_weekday() static_assert(weekday{3}[2].weekday() == weekday{3}); static_assert(weekday{3}[last].weekday() == weekday{3}); + // Test for UB (overflow). + { + using rep = days::rep; + using std::numeric_limits; + constexpr weekday max{sys_days{days{numeric_limits::max()}}}; + constexpr weekday min{sys_days{days{numeric_limits::min()}}}; + } + static_assert(weekday{sys_days{1900y/January/1}} == Monday); static_assert(weekday{sys_days{1970y/January/1}} == Thursday); static_assert(weekday{sys_days{2020y/August/21}} == Friday); -- 2.41.0