From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57209) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fEGjs-00051a-Kr for qemu-devel@nongnu.org; Thu, 03 May 2018 12:05:50 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fEGjn-0003BX-HA for qemu-devel@nongnu.org; Thu, 03 May 2018 12:05:48 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:42034) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fEGjn-0003B3-5U for qemu-devel@nongnu.org; Thu, 03 May 2018 12:05:43 -0400 Received: from pps.filterd (m0098404.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w43G4r9M076243 for ; Thu, 3 May 2018 12:05:42 -0400 Received: from e36.co.us.ibm.com (e36.co.us.ibm.com [32.97.110.154]) by mx0a-001b2d01.pphosted.com with ESMTP id 2hr4kvk6tf-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Thu, 03 May 2018 12:05:41 -0400 Received: from localhost by e36.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 3 May 2018 10:05:41 -0600 References: <20180502125221.4877-1-cohuck@redhat.com> <20180503174412.359494fb.cohuck@redhat.com> From: Farhan Ali Date: Thu, 3 May 2018 12:05:28 -0400 MIME-Version: 1.0 In-Reply-To: <20180503174412.359494fb.cohuck@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Message-Id: <5baae3f1-07ff-3ba0-fb83-81e0eb9a0240@linux.ibm.com> Subject: Re: [Qemu-devel] [PATCH] s390-ccw: force diag 308 subcode to unsigned long List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Cornelia Huck Cc: Christian Borntraeger , Thomas Huth , qemu-s390x@nongnu.org, qemu-devel@nongnu.org, qemu-stable@nongnu.org On 05/03/2018 11:44 AM, Cornelia Huck wrote: > On Thu, 3 May 2018 11:25:08 -0400 > Farhan Ali wrote: > >> On 05/02/2018 08:52 AM, Cornelia Huck wrote: >>> We currently pass an integer as the subcode parameter. However, >>> the upper bits of the register containing the subcode need to >>> be 0, which is not guaranteed unless we explicitly specify the >>> subcode to be an unsigned long value. >>> >>> Fixes: d046c51dad3 ("pc-bios/s390-ccw: Get device address via diag 308/6") >>> Cc:qemu-stable@nongnu.org >>> Signed-off-by: Cornelia Huck >> >> Sorry for my ignorance, but is there a C standard that says upper bits >> of an int is not guaranteed to be 0? > > The value (5 resp. 6) is small enough to fit into a regular integer, > and the compiler generated a lhi for the load, which did not change any > upper values that might have been in the register previously. Telling > the compiler to treat the value as an unsigned long makes it generate a > lghi. > This makes sense now. Thanks for the explanation :)