Re: Running the gdb 7.12.1 testsuite breaks kernel 4.13.8 on C8000

From: Helge Deller <deller@gmx.de>
To: Rolf Eike Beer <eike-kernel@sf-tec.de>, linux-parisc@vger.kernel.org
Subject: Re: Running the gdb 7.12.1 testsuite breaks kernel 4.13.8 on C8000
Date: Sat, 27 Jan 2018 19:41:03 +0100	[thread overview]
Message-ID: <d071a2c0-fb08-639e-36ef-b769e195cfff@gmx.de> (raw)
In-Reply-To: <2594108.Soefd0VDuM@daneel.sf-tec.de>

Hi Rolf,

On 27.01.2018 18:42, Rolf Eike Beer wrote:
> Am Freitag, 26. Januar 2018, 23:31:46 schrieb Helge Deller:
>> On 25.01.2018 16:36, Rolf Eike Beer wrote:
>>> John David Anglin wrote:
>>>> On 2018-01-25 3:59 AM, Rolf Eike Beer wrote:
>>>>> [  909.756303] Kernel panic - not syncing: Bad Address (null pointer
>>>>> deref?) [  909.756303] ---[ end Kernel panic - not syncing: Bad Address
>>>>> (null pointer deref?)
>>>>>
>>>>> This is actually the second place where it breaks, before that I had the
>>>>> same>> 
>>>>> with this test (twice):
>>>> Would you post the PIM dump of the most recent HPMC in the service
>>>> menu?
>>>
>>> The service menu does not give any information, as in this older bug:
>>> https://bugs.gentoo.org/481768
>> FWIW, I've tested the testcase from
>>  https://bugs.gentoo.org/481768
>> on a debian system:
>> Linux panama.osuosl.org 4.14.0-2-parisc64-smp #1 SMP Debian 4.14.7-1
>> (2017-12-28) parisc64 GNU/Linux gdb was version 7.12-6+b1
>>
>> On debian I can not reproduce the crash.
>>
>> With this sequence:
>> (gdb) break gdb-crash.c:14
>> (gdb) run
>> (gdb) set tp = {0,0}
>>
>> tp isn't initialized yet before you reach line 25, and as such it points to
>> random memory. I you try to set tp, it depends on what happens (but agreed,
>> it shouldn't crash the kernel).
>>
>> The Debian kernel hasn't any additional hppa-specific patches.
> 
> I'm using vanilla, so nothing on my side either.
> 
>>>> Also needed
>>>> is the assembler dump of the routine where the HPMC occurred in your
>>>> kernel.  You need the
>>>> 64-bit version of objdump for this.
>>
>> I wonder why there isn't any kernel backtrace...
> 
> This was with "dmesg -n 8". Without it has shown only the "Bad address" and 
> "end Kernel panic" lines, which is IMHO bad by itself.
> 
>> Does gentoo uses special compiler-optimization flags?
> 
> I have none.
> 
>>> I have put the kernel on https://opensource.sf-tec.de/c8000-kernel.tar.xz
>>
>> I'd suggest you put some debugging code in your kernel, e.g. in
>> compat_ptrace_request() in kernel/ptrace.c.
>> I think gdb uses PTRACE_POKEDATA to set some userspace memory of a process.
>> It's generic code, so I wonder why it should crash on parisc.
>>
>> You may look at compat_arch_ptrace() in arch/parisc/kernel/ptrace.c too, but
>> it doesn't touch memory as far as I can see...
> 
> I will not be able to touch any of this until at least mid of next week. If 
> you want to give it a try, check gdb 7.12.1 testsuite. It was one of the first 
> tests that hit this.

As I said before, I can't reproduce this on debian.
gdb does not (and never has) crash(ed) the system, as can be seen in the various build logs:
 https://buildd.debian.org/status/logs.php?pkg=gdb&arch=hppa
e.g.:
 https://buildd.debian.org/status/fetch.php?pkg=gdb&arch=hppa&ver=7.12-6%2Bb1&stamp=1507997688&raw=0

Helge