linux-kernel - Re: sparc gcc 7.1 compile issue

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Date:   Sun, 4 Jun 2017 17:09:10 +0200
From:   John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
To:     Waldemar Brodkorb <wbx@...nadk.org>
Cc:     David Miller <davem@...emloft.net>, linux-kernel@...r.kernel.org,
        sparclinux@...r.kernel.org
Subject: Re: sparc gcc 7.1 compile issue

Hi Waldemar!

On 06/04/2017 04:40 PM, Waldemar Brodkorb wrote:
>> So, in your point of view it's perfectly fine if an application is able
>> to crash the whole kernel with just user privileges?
>>
>> Shouldn't the kernel be able to cope with that?
> 
> I think he means your kernel you are running might be miscompiled
> with gcc 7.1.

The kernel wasn't compiled by 7.1. It was built with 6.3:

[    0.000000] PROMLIB: Sun IEEE Boot Prom 'OBP 4.38.8 2017/02/22 13:51'
[    0.000000] PROMLIB: Root node compatible: sun4v
[    0.000000] Linux version 4.12.0-rc1-sparc64-smp (debian-kernel@...ts.debian.org) (gcc version 6.3.0 20170510 (Debian 6.3.0-17) ) #1 SMP Debian
4.12~rc1-1~exp1~sparc64 (2017-05-17)

> What kernel version you are running?

This has been haunting us since around kernel 4.6 or so. It also
only shows when building with many parallel jobs.

> Which compiler you used to generate the running kernel?

6.3.0 20170510 from the gcc-6 branch.

> If it is gcc 7.1, what is if you try to
> reproduce the crash with the same kernel version compiled with gcc
> 6.3?

It's simply gcc-7's testsuite that's crashing the kernel since kernel
versions around 4.6. We haven't done any kernel compiles with gcc-7.1
yet since gcc-7.1 not yet the default compiler, we're just building the
package in Debian experimental.

> Wouldn't this show if it is a compiler or kernel bug?

Yes and I think the data suggests it's rather a kernel bug than a bug
in gcc.

Adrian

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer - glaubitz@...ian.org
`. `'   Freie Universitaet Berlin - glaubitz@...sik.fu-berlin.de
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