linux-kernel - arm64 kvm built with clang doesn't boot

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Date:   Fri, 16 Mar 2018 14:49:00 +0100
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Stephen Hines <srhines@...gle.com>,
        Greg Hackmann <ghackmann@...gle.com>,
        Christoffer Dall <christoffer.dall@...aro.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        kvmarm@...ts.cs.columbia.edu, LKML <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>
Cc:     kernel-dynamic-tools <kernel-dynamic-tools@...gle.com>
Subject: arm64 kvm built with clang doesn't boot

Hi!

I've recently tried to boot clang built kernel on real hardware
(Odroid C2 board) instead of using a VM. The issue that I stumbled
upon is that arm64 kvm built with clang doesn't boot.

Adding -fno-jump-tables compiler flag to arch/arm64/kvm/* helps. There
was a patch some time ago that did exactly that
(https://patchwork.kernel.org/patch/10060381/), but it wasn't accepted
AFAICT (see the discussion on that thread).

What would be the best way to get this fixed?

I've also had to disable CONFIG_JUMP_LABEL to get the kernel boot
(even without kvm enabled), but that might be a different (though
related) issue.

Thanks!