From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 99A85C432C3 for ; Fri, 22 Nov 2019 08:06:14 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 63E0920659 for ; Fri, 22 Nov 2019 08:06:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="dZJ43e6U" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 63E0920659 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:48166 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iY3xF-0000x1-9r for qemu-devel@archiver.kernel.org; Fri, 22 Nov 2019 03:06:13 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:42021) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iY3s5-0002yO-6I for qemu-devel@nongnu.org; Fri, 22 Nov 2019 03:00:54 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iY3rz-00007r-UW for qemu-devel@nongnu.org; Fri, 22 Nov 2019 03:00:51 -0500 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:23452 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iY3rz-00007E-P6 for qemu-devel@nongnu.org; Fri, 22 Nov 2019 03:00:47 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1574409646; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=aCU61u+GqUXLUmT+QA2tuhXLyqlWLyB7Zmg1NU+CZRk=; b=dZJ43e6UvxZBejdNdW9FaTXnUB72+BWlSWW2hksN17xyY1A6KfrLlVwOb3xWxQs0QordsV uSeeaxXjlTC+8iKlmWjg3MNZPfjRxIE3UwNhmCbwGRL0uAzySu5ImguVbFbpuVNxKupzOj xUkW8aC8vsEO01NjnlyQGE0oaxjMKjk= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-285-_QR7sY5NOaap47YNikMrUw-1; Fri, 22 Nov 2019 03:00:42 -0500 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 70195DC23; Fri, 22 Nov 2019 08:00:41 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-116-134.ams2.redhat.com [10.36.116.134]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 190C976FE5; Fri, 22 Nov 2019 08:00:41 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 8F43511366CC; Fri, 22 Nov 2019 09:00:39 +0100 (CET) From: Markus Armbruster To: qemu-devel@nongnu.org Subject: [PATCH v3 2/2] util/cutils: Fix incorrect integer->float conversion caught by clang Date: Fri, 22 Nov 2019 09:00:39 +0100 Message-Id: <20191122080039.12771-3-armbru@redhat.com> In-Reply-To: <20191122080039.12771-1-armbru@redhat.com> References: <20191122080039.12771-1-armbru@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-MC-Unique: _QR7sY5NOaap47YNikMrUw-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.120 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Fangrui Song , richard.henderson@linaro.org, dgilbert@redhat.com, quintela@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" From: Fangrui Song Clang does not like do_strtosz()'s code to guard against overflow: qemu/util/cutils.c:245:23: error: implicit conversion from 'unsigned lo= ng' to 'double' changes value from 18446744073709550592 to 1844674407370955= 1616 [-Werror,-Wimplicit-int-float-conversion] The warning will be enabled by default in clang 10. It is not available for clang <=3D 9. val * mul >=3D 0xfffffffffffffc00 is indeed wrong. 0xfffffffffffffc00 is not representable exactly as double. It's half-way between the representable values 0xfffffffffffff800 and 0x10000000000000000. Which one we get is implementation-defined. Bad. We want val * mul > (the largest uint64_t exactly representable as double). That's 0xfffffffffffff800. Write it as nextafter(0x1p64, 0) with a suitable comment. Signed-off-by: Fangrui Song Reviewed-by: Markus Armbruster [Patch split, commit message improved] Signed-off-by: Markus Armbruster --- util/cutils.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/util/cutils.c b/util/cutils.c index fd591cadf0..77acadc70a 100644 --- a/util/cutils.c +++ b/util/cutils.c @@ -239,10 +239,12 @@ static int do_strtosz(const char *nptr, const char **= end, goto out; } /* - * Values >=3D 0xfffffffffffffc00 overflow uint64_t after their trip - * through double (53 bits of precision). + * Values near UINT64_MAX overflow to 2**64 when converting to double + * precision. Compare against the maximum representable double precis= ion + * value below 2**64, computed as "the next value after 2**64 (0x1p64)= in + * the direction of 0". */ - if ((val * mul >=3D 0xfffffffffffffc00) || val < 0) { + if ((val * mul > nextafter(0x1p64, 0)) || val < 0) { retval =3D -ERANGE; goto out; } --=20 2.21.0