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Date:   Wed, 29 Nov 2017 15:30:08 -0800
From:   Sami Tolvanen <>
To:     Nicholas Piggin <>
Cc:     Alex Matveev <>, Andi Kleen <>,
        Ard Biesheuvel <>,
        Greg Hackmann <>,
        Kees Cook <>,,,, Mark Rutland <>,
        Masahiro Yamada <>,
        Maxim Kuvyrkov <>,
        Michal Marek <>,
        Nick Desaulniers <>,
        Yury Norov <>,
        Matthias Kaehlcke <>
Subject: Re: [v2,12/18] kbuild: add support for clang LTO

On Tue, Nov 21, 2017 at 11:01:52AM +1000, Nicholas Piggin wrote:
> I just wonder are you doing this because there is some worthwhile
> performance gain? Or to enable more testing and development of LTO?
> Any clues for why a user would want to enable it.

I'm primarily interested in CFI, which with clang requires LTO; not
for the optimizations, but for source visibility. We do expect to see
performance improvements with LTO though, especially if combined with

> Thanks, if you could. Possibly file a request with LLVMgold too, it
> seems to be that toolchain support for archives is quite strong, so it
> will be good to keep pushing for that.

It turns out LLVMgold is fine with mixed IR/object archives, but we need
to use llvm-ar to generate symbol tables for them, and there are some
compatibility issues with objdump that I had to work around. I'll send
v3 for review once I receive some feedback for the clang/gold patches we
need first.


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