linux-kernel - Re: 4.17.x won't boot due to "x86/boot/compressed/64: Handle 5-level paging boot if kernel is above 4G"

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Date:   Tue, 3 Jul 2018 16:19:36 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Bernhard Rosenkraenzer <bero@...dev.ch>
cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Gabriel C <nix.or.die@...il.com>,
        Benjamin Gilbert <bgilbert@...hat.com>,
        linux-x86_64@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>
Subject: Re: 4.17.x won't boot due to "x86/boot/compressed/64: Handle 5-level
 paging boot if kernel is above 4G"

On Tue, 3 Jul 2018, Bernhard Rosenkraenzer wrote:
> On Tuesday, July 03, 2018 16:02 CEST, Thomas Gleixner <tglx@...utronix.de> wrote:
> > On Tue, 3 Jul 2018, Kirill A. Shutemov wrote:
> > > On Tue, Jul 03, 2018 at 01:24:49PM +0200, Gabriel C wrote:
> > > > 2018-07-01 23:32 GMT+02:00 Benjamin Gilbert <bgilbert@...hat.com>:
> > > > > On Sun, Jul 01, 2018 at 05:15:59PM -0400, Benjamin Gilbert wrote:
> > > > >> 4.17 kernels built with the CoreOS Container Linux toolchain and kconfig,
> > > > >> up to and including 4.17.3, fail to boot on AMD64 running in (at least)
> > > > >> QEMU/KVM.  No messages are shown post-GRUB; the VM instantly reboots.
> > > > >> Reverting commit 194a9749c73d ("x86/boot/compressed/64: Handle 5-level
> > > > >> paging boot if kernel is above 4G") fixes it.  I've attached our kernel
> > > > >> config for reference, and am happy to test patches, provide sample QCOW
> > > > >> images, etc.
> > > > >
> > > >
> > > > Also see https://bugzilla.kernel.org/show_bug.cgi?id=200385 ,
> > > >
> > > > 0a1756bd2897951c03c1cb671bdfd40729ac2177 is acting up
> > > > too with the same symptoms
> > >
> > > I tracked it down to -flto in LDFLAGS. I'll look more into this.
> >
> > And what sets -flto in LDFLAGS? I can't find anything in the kernel
> > build/Makefiles.
> 
> The kernel doesn't use -flto by default. Some people (and distros) set
> -flto in CFLAGS and LDFLAGS manually hoping to get a few extra
> optimizations.  This never caused any problems before 0a1756bd - would be
> nice to keep it working.

Maybe it never caused any obvious problems, but there is a reason why LTO
is not supported by the kernel, GCC and its LTO history being one of them.

Thanks,

	tglx