linux-kernel - Re: [PATCH v2 00/18] Add support for clang LTO

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Message-ID: <20171120152139.mfqthlbneeeiythr@lakrids.cambridge.arm.com>
Date:   Mon, 20 Nov 2017 15:21:40 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Alex Matveev <alxmtvv@...il.com>, Andi Kleen <ak@...ux.intel.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Greg Hackmann <ghackmann@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Maxim Kuvyrkov <maxim.kuvyrkov@...aro.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Yury Norov <ynorov@...iumnetworks.com>,
        Matthias Kaehlcke <mka@...omium.org>
Subject: Re: [PATCH v2 00/18] Add support for clang LTO

Hi,

On Wed, Nov 15, 2017 at 01:34:10PM -0800, Sami Tolvanen wrote:
> This series adds build system support for compiling the kernel with clang
> Link Time Optimization (LTO), using GNU gold with the LLVMgold plug-in
> for linking. 

As a high-level comment, this path series is rather confusing for
maintainers, since it's a mixture of basic support, workarounds, and a
new feature, and the commit messages aren't that helpful for those of us
unfamiliar with clang.

It would be *very* helpful if this could be split into a few smaller
patch series that built atop of each other.

Would it be possible to split this into:

(1) (basic) arm64 clang support
(2) gold support (no LTO)
(3) LTO support

... with any necessary workarounds added as-required to the relevant
series?

I think (1) is just the clang-version, -mno-implicit-float, and KVM
patches, and that might stand a chance of getting in soon. IIUC that
fixes the outstanding issues with basic clang support, and would give us
all a common baseline for review, testing, and future debugging.

Thanks,
Mark.