From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sebastian Riemer Subject: Re: Why is (2 < 2) true? Is it a gcc bug? Date: Fri, 17 Jan 2014 17:40:10 +0100 Message-ID: <52D95CEA.809@profitbricks.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from mail-bk0-f44.google.com ([209.85.214.44]:43169 "EHLO mail-bk0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750937AbaAQQkO (ORCPT ); Fri, 17 Jan 2014 11:40:14 -0500 Received: by mail-bk0-f44.google.com with SMTP id ej10so1727450bkb.3 for ; Fri, 17 Jan 2014 08:40:13 -0800 (PST) In-Reply-To: Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: "Dorau, Lukasz" Cc: "linux-kernel@vger.kernel.org" , "linux-scsi@vger.kernel.org" On 17.01.2014 14:55, Dorau, Lukasz wrote: > 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. to_pci_info() can return NULL in dev_get_drvdata(). The use of ARRAY_SIZE() is inappropriate. #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) + __must_be_array(arr)) #define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0])) #define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:-!!(e); })) I would say that this was supposed to trigger a build error but it didn't and added 1 to the loop end condition. Can you test putting SCI_MAX_CONTROLLERS to the loop end condition, please? Cheers, Sebastian