linux-kernel - Re: BUG: Sporadic crashes with current Linus tree

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Date:   Fri, 13 Oct 2017 10:22:54 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Dmitry Safonov <0x7f454c46@...il.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        X86 ML <x86@...nel.org>
Subject: Re: BUG: Sporadic crashes with current Linus tree

On Fri, Oct 13, 2017 at 8:54 AM, Dmitry Safonov <0x7f454c46@...il.com> wrote:
> Hi Tglx, Andy,
>
> Sorry for old-posting,
>
> 2017-09-15 8:09 GMT+01:00 Thomas Gleixner <tglx@...utronix.de>:
>> On Thu, 14 Sep 2017, Andy Lutomirski wrote:
>>> On Thu, Sep 14, 2017 at 9:00 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
>>> > On Thu, 14 Sep 2017, Andy Lutomirski wrote:
>>> >> On Thu, Sep 14, 2017 at 12:38 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
>>> >> > Hi!
>>> >> >
>>> >> > I've seen the following crash sporadically with commit 46c1e79fee:
>>> >> >
>>> >> > Have not seen that with 3882a734c19b, though I saw the PCID warnings on
>>> >> > that machine.
>>> >> >
>>> >> > I have no idea how to reproduce so bisecting is pretty much pointless. Any
>>> >> > idea what to do?
>>> >>
>>> >> Does tools/testing/selftests/x86/sigreturn_64 reproduce it?
>>> >
>>> > Will try tomorrow once I figured out how to compile that stuff. Invoking a
>>> > simple make in that directory fails.
>>>
>>> What's the error?  It works for me.
>>
>> gcc -m64 -o /home/tglx/work/kernel/linus/linux/tools/testing/selftests/x86/sysret_ss_attrs_64 -O2 -g -std=gnu99 -pthread -Wall  sysret_ss_attrs.c thunks.S -lrt -ldl
>> /usr/bin/ld: /tmp/cco4vSkU.o: relocation R_X86_64_32S against `.text' can not be used when making a shared object; recompile with -fPIC
>> /usr/bin/ld: final link failed: Nonrepresentable section on output
>> collect2: error: ld returned 1 exit status
>
> Had the same issue in copied thunks.S helper to CRIU.
> As I wanted to compile CRIU as pie also (which is the default now
> in some distributions), I fixed it up by using %rip-relative addressing
> and pushing segment descriptor to stack before long-jumping.
> Not sure if that's the issue for the selftest as it can be just always
> compiled as pic.
>
> Anyway, here is the commit if you want to look:
> https://github.com/0x7f454c46/criu/commit/cf36ea5d8408bf1e42c3bd21b9594369ea7123fb

Thanks!

The problem is that I need to have some text below 4 GB, and that's
currently guaranteed by a non-PIE build.  And I'm lazy :)

>
> --
>              Dmitry