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From:   Lukasz Majczak <lma@semihalf.com>
Date:   Wed, 9 Jun 2021 09:11:18 +0200
Message-ID: <CAFJ_xbp5YzYNQWEJLDySyC_bWUsirq=P03k8HHW=B4sH0V_uUg@mail.gmail.com>
Subject: Re: [PATCH v3 16/16] objtool,x86: Rewrite retpoline thunk calls
To:     Nathan Chancellor <nathan@kernel.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        =?UTF-8?B?RsSBbmctcnXDrCBTw7JuZw==?= <maskray@google.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Guenter Roeck <groeck@google.com>,
        Juergen Gross <jgross@suse.com>,
        =?UTF-8?Q?=C5=81ukasz_Bartosik?= <lb@semihalf.com>,
        LKML <linux-kernel@vger.kernel.org>, mbenes@suse.com,
        =?UTF-8?Q?Rados=C5=82aw_Biernacki?= <rad@semihalf.com>,
        upstream@semihalf.com,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        Sami Tolvanen <samitolvanen@google.com>
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wt., 8 cze 2021 o 20:49 Nathan Chancellor <nathan@kernel.org> napisa=C5=82(=
a):
>
> On 6/8/2021 11:17 AM, Peter Zijlstra wrote:
> > On Tue, Jun 08, 2021 at 10:29:56AM -0700, Nathan Chancellor wrote:
> >> Unfortunately, this is the VM provided by the Windows Subsystem for Li=
nux so
> >> examining it is nigh-impossible :/ I am considering bisecting the tran=
sforms
> >> that objtool does to try and figure out the one that causes the machin=
e to
> >> fail to boot or try to reproduce in a different hypervisor, unless you=
 have
> >> any other ideas.
> >
> > Does breaking Windows earn points similar to breaking the binary
> > drivers? :-) :-)
>
> :)
>
> > The below should kill this latest transform and would quickly confirm i=
f
> > the that is causing your problem. If that's not it, what was your last
> > known working version?
>
> Yes, that diff gets me back to booting. I will see if I can figure out
> the exact rewrite that blows everything up.
>
> > diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> > index e5947fbb9e7a..d0f231b9c5a1 100644
> > --- a/tools/objtool/check.c
> > +++ b/tools/objtool/check.c
> > @@ -1857,10 +1857,10 @@ static int decode_sections(struct objtool_file =
*file)
> >        * Must be after add_special_section_alts(), since this will emit
> >        * alternatives. Must be after add_{jump,call}_destination(), sin=
ce
> >        * those create the call insn lists.
> > -      */
> >       ret =3D arch_rewrite_retpolines(file);
> >       if (ret)
> >               return ret;
> > +      */
> >
> >       return 0;
> >   }
> >
>
> Cheers,
> Nathan

Hi Peter,

I'm sorry I was on vacation last week - do you still need the requested deb=
ugs?

Best regards,
Lukasz