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, 03 Jul 2018 16:07:43 +0200
From:   "Bernhard Rosenkraenzer" <bero@...dev.ch>
To:     "Thomas Gleixner" <tglx@...utronix.de>
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 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.

ttyl
bero