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From:   Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date:   Sun, 2 Feb 2020 10:32:11 +0100
Message-ID: <CAKv+Gu-QfKgXStODzbpwSFTHsgiSzFVKdbYiuhVPQF+XtV2MEA@mail.gmail.com>
Subject: Re: EFI boot crash regression (was: Re: 5.6-### doesn't boot)
To:     Ingo Molnar <mingo@kernel.org>
Cc:     =?UTF-8?Q?J=C3=B6rg_Otte?= <jrg.otte@gmail.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Ard Biesheuvel <ardb@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "the arch/x86 maintainers" <x86@kernel.org>
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On Sun, 2 Feb 2020 at 10:22, Ingo Molnar <mingo@kernel.org> wrote:
>
>
> * Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
>
> > Hello J=C3=B6rg,
> >
> > Could you please try whether the change below fixes the issue?
> >
> > diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
> > index 59f7f6d60cf6..ae923ee8e2b4 100644
> > --- a/arch/x86/platform/efi/efi.c
> > +++ b/arch/x86/platform/efi/efi.c
> > @@ -308,7 +308,7 @@ static void __init efi_clean_memmap(void)
> >                         .phys_map =3D efi.memmap.phys_map,
> >                         .desc_version =3D efi.memmap.desc_version,
> >                         .desc_size =3D efi.memmap.desc_size,
> > -                       .size =3D data.desc_size * (efi.memmap.nr_map -=
 n_removal),
> > +                       .size =3D efi.memmap.desc_size * (efi.memmap.nr=
_map - n_removal),
> >                         .flags =3D 0,
>
> Oh, I actually noticed this one, but convinced myself that it's correct,
> because GCC didn't warn about uninitialized data.
>
> But maybe in this weird case data.desc_size as used within its own
> initializer is zero?
>

Something like that, yes. Note that size and desc_size appear in
opposite order in the struct definition, and this may also affect how
the compiler handles this.