From nobody Wed Nov 5 16:57:09 2025 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) client-ip=208.118.235.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org Return-Path: Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) by mx.zohomail.com with SMTPS id 1536440685974453.0000182609457; Sat, 8 Sep 2018 14:04:45 -0700 (PDT) Received: from localhost ([::1]:45241 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fykPM-0006EP-MP for importer@patchew.org; Sat, 08 Sep 2018 17:04:44 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:59298) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fyhwD-0003Km-0J for qemu-devel@nongnu.org; Sat, 08 Sep 2018 14:26:46 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fyhvm-0005D7-FL for qemu-devel@nongnu.org; Sat, 08 Sep 2018 14:26:28 -0400 Received: from hillend.cent.gla.ac.uk ([130.209.16.102]:45122) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fyhuW-0000Ro-PR; Sat, 08 Sep 2018 14:24:45 -0400 Received: from cas08.campus.gla.ac.uk ([130.209.14.165]) by hillend.cent.gla.ac.uk with esmtp (Exim 4.72) (envelope-from ) id 1fyhuH-0001gz-F1; Sat, 08 Sep 2018 19:24:29 +0100 Received: from mornington.dcs.gla.ac.uk (130.209.253.38) by cas08.campus.gla.ac.uk (130.209.14.165) with Microsoft SMTP Server (TLS) id 15.0.1395.4; Sat, 8 Sep 2018 19:24:28 +0100 Date: Sat, 8 Sep 2018 19:22:05 +0100 From: Tony Garnock-Jones To: Message-ID: <20180908182205.GB409@mornington.dcs.gla.ac.uk> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.10.1 (2018-07-13) X-Originating-IP: [130.209.253.38] X-ClientProxiedBy: cas07.campus.gla.ac.uk (130.209.14.164) To cas08.campus.gla.ac.uk (130.209.14.165) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: Solaris 10 X-Received-From: 130.209.16.102 X-Mailman-Approved-At: Sat, 08 Sep 2018 17:03:07 -0400 Subject: [Qemu-devel] [PATCH] linux-user: write(fd, NULL, 0) parity with linux's treatment of same X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-trivial@nongnu.org, Riku Voipio , qemu-stable@nongnu.org, Laurent Vivier Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail: RSF_0 Z_629925259 SPT_0 Content-Type: text/plain; charset="utf-8" Bring linux-user write(2) handling into line with linux for the case of a 0-byte write with a NULL buffer. Based on a patch originally written by Zhuowei Zhang. Addresses https://bugs.launchpad.net/qemu/+bug/1716292. From Zhuowei Zhang's patch (https://lists.gnu.org/archive/html/qemu-devel/2= 017-09/msg08073.html): Linux returns success for the special case of calling write with a zero-length NULL buffer: compiling and running int main() { ssize_t ret =3D write(STDOUT_FILENO, NULL, 0); fprintf(stderr, "write returned %ld\n", ret); return 0; } gives "write returned 0" when run directly, but "write returned -1" in QEMU. This commit checks for this situation and returns success if found. Subsequent discussion raised the following questions (and my answers): - Q. Should TARGET_NR_read pass through to safe_read in this situation too? A. I'm wary of changing unrelated code to the specific problem I'm addressing. TARGET_NR_read is already consistent with Linux for this case. - Q. Do pread64/pwrite64 need to be changed similarly? A. Experiment suggests not: both linux and linux-user yield -1 for NULL 0-length reads/writes. Signed-off-by: Tony Garnock-Jones Reviewed-by: Laurent Vivier Reviewed-by: Philippe Mathieu-Daud=C3=A9 --- linux-user/syscall.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/linux-user/syscall.c b/linux-user/syscall.c index 850b72a0c7..8f46540534 100644 --- a/linux-user/syscall.c +++ b/linux-user/syscall.c @@ -8168,6 +8168,9 @@ static abi_long do_syscall1(void *cpu_env, int num, a= bi_long arg1, } return ret; case TARGET_NR_write: + if (arg2 =3D=3D 0 && arg3 =3D=3D 0) { + return get_errno(safe_write(arg1, 0, 0)); + } if (!(p =3D lock_user(VERIFY_READ, arg2, arg3, 1))) return -TARGET_EFAULT; if (fd_trans_target_to_host_data(arg1)) { -- 2.18.0 [University of Glasgow: The Times Scottish University of the Year 2018]