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

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Message-ID: <20180316171349.fodlraapz2sq2hhs@lakrids.cambridge.arm.com>
Date:   Fri, 16 Mar 2018 17:13:49 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     marc.zyngier@....com, Andrey Konovalov <andreyknvl@...gle.com>,
        Stephen Hines <srhines@...gle.com>,
        Greg Hackmann <ghackmann@...gle.com>,
        christoffer.dall@...aro.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-dynamic-tools <kernel-dynamic-tools@...gle.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        takahiro.akashi@...aro.org
Subject: Re: arm64 kvm built with clang doesn't boot

On Fri, Mar 16, 2018 at 04:52:08PM +0000, Nick Desaulniers wrote:
> + Sami (Google), Takahiro (Linaro)
> 
> Just so I fully understand the problem enough to articulate it, we'd be
> looking for the compiler to keep the jump tables for speed (I would guess
> -fno-jump-tables would emit an if-else chain) but only emit relative jumps
> (not absolute jumps)?

Our main concern is that there is no absolute addressing. If that rules
out using a relative jump table, that's ok.

We want to avoid the fragility of collecting -f-no-* options as future
compiler transformations end up introducing absolute addressing.

Thanks,
Mark.