Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752472AbaAQNzZ (ORCPT ); Fri, 17 Jan 2014 08:55:25 -0500 Received: from mga09.intel.com ([134.134.136.24]:52408 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751382AbaAQNzU convert rfc822-to-8bit (ORCPT ); Fri, 17 Jan 2014 08:55:20 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.95,670,1384329600"; d="scan'208";a="440399740" From: "Dorau, Lukasz" To: "linux-kernel@vger.kernel.org" , "linux-scsi@vger.kernel.org" Subject: RE: Why is (2 < 2) true? Is it a gcc bug? Thread-Topic: Why is (2 < 2) true? Is it a gcc bug? Thread-Index: Ac8TiNMTmnptR9ryRvWTI5/er276UQAAgwFg Date: Fri, 17 Jan 2014 13:55:00 +0000 Message-ID: References: In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [163.33.239.181] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Friday, January 17, 2014 2:37 PM Dorau, Lukasz wrote: > > Hi > > My story is very simply... > I applied the following patch: > > diff --git a/drivers/scsi/isci/init.c b/drivers/scsi/isci/init.c > --- a/drivers/scsi/isci/init.c > +++ b/drivers/scsi/isci/init.c > @@ -698,8 +698,11 @@ static int isci_pci_probe(struct pci_dev *pdev, const struct > pci_device_id *id) > if (err) > goto err_host_alloc; > > - for_each_isci_host(i, isci_host, pdev) > + for_each_isci_host(i, isci_host, pdev) { > + pr_err("(%d < %d) == %d\n",\ > + i, SCI_MAX_CONTROLLERS, (i < SCI_MAX_CONTROLLERS)); > scsi_scan_host(to_shost(isci_host)); > + } > > return 0; > > -- > 1.8.3.1 > > Then I issued the command 'modprobe isci' on platform with two SCU controllers > (Patsburg D or T chipset) > and received the following, very strange, output: > > (0 < 2) == 1 > (1 < 2) == 1 > (2 < 2) == 1 > > Can anyone explain why (2 < 2) is true? Is it a gcc bug? > > (The kernel was compiled using gcc version 4.8.2.) > Some additional information: The loop 'for' in macro ' for_each_isci_host ' defined as (drivers/scsi/isci/host.h:313): #define for_each_isci_host(id, ihost, pdev) \ for (id = 0, ihost = to_pci_info(pdev)->hosts[id]; \ id < ARRAY_SIZE(to_pci_info(pdev)->hosts) && ihost; \ ihost = to_pci_info(pdev)->hosts[++id]) should be executed only for i = 0 and 1, because: ARRAY_SIZE(to_pci_info(pdev)->hosts) = SCI_MAX_CONTROLLERS = 2 but it was executed also for i=2 regardless the above loop's end condition. Lukasz -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/