linux-kernel - Re: [PATCH v3 16/16] objtool,x86: Rewrite retpoline thunk calls

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Date:   Wed, 9 Jun 2021 09:11:18 +0200
From:   Lukasz Majczak <lma@...ihalf.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Fāng-ruì Sòng <maskray@...gle.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Guenter Roeck <groeck@...gle.com>,
        Juergen Gross <jgross@...e.com>,
        Łukasz Bartosik <lb@...ihalf.com>,
        LKML <linux-kernel@...r.kernel.org>, mbenes@...e.com,
        Radosław Biernacki <rad@...ihalf.com>,
        upstream@...ihalf.com,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: Re: [PATCH v3 16/16] objtool,x86: Rewrite retpoline thunk calls

wt., 8 cze 2021 o 20:49 Nathan Chancellor <nathan@...nel.org> napisał(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 Linux so
> >> examining it is nigh-impossible :/ I am considering bisecting the transforms
> >> that objtool does to try and figure out the one that causes the machine 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 if
> > 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(), since
> >        * those create the call insn lists.
> > -      */
> >       ret = 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 debugs?

Best regards,
Lukasz