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

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Message-ID: <CAFLxGvz3FKU4rgjF_uZsggjvw8TQw_Hcp42GC8Zr-wg5kiwc-w@mail.gmail.com>
Date:	Fri, 17 Jan 2014 14:58:10 +0100
From:	Richard Weinberger <richard.weinberger@...il.com>
To:	"Dorau, Lukasz" <lukasz.dorau@...el.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>
Subject: Re: Why is (2 < 2) true? Is it a gcc bug?

On Fri, Jan 17, 2014 at 2:37 PM, Dorau, Lukasz <lukasz.dorau@...el.com> 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.)
>

Can you reproduce this using a standalone test?
I.e:
#include <assert.h>

int main()
{
        assert(2 < 2 != 1);

        return 0;
}

-- 
Thanks,
//richard
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