linux-kernel - Why is (2 < 2) true? Is it a gcc bug?

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Message-ID: <D9FFE20C522965449E182ACE73889AEB1A6A340F@IRSMSX105.ger.corp.intel.com>
Date:	Fri, 17 Jan 2014 13:37:17 +0000
From:	"Dorau, Lukasz" <lukasz.dorau@...el.com>
To:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>
Subject: Why is (2 < 2) true? Is it a gcc bug?

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.)

Lukasz

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