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    SubjectRe: [PATCH 20/21] Kbuild, lto: Add Link Time Optimization support
    On Sat, Jan 27, 2018 at 01:15:49AM +0100, Arnd Bergmann wrote:
    > On Mon, Nov 27, 2017 at 10:34 PM, Andi Kleen <andi@firstfloor.org> wrote:
    > > From: Andi Kleen <ak@linux.intel.com>
    > > - Add a new LDFINAL variable that controls the final link
    > > for vmlinux or module. In this case we call gcc-ld instead
    > > of ld, to run the LTO step.
    >
    > When I tried this out on allmodconfig (following the lwn article), I ran into
    > a number of warnings:

    Thanks for testing. Yes it's a known issue: during one module build
    when modpost looks at the file it is still in LTO format, and
    modpost doesn't understand the LTO symbol table. I had a patch
    to teach it to it at some point, but it got lost somewhere.
    The LLVM LTO patchkit has a different solution that actually
    fixes the sequence to run modpost only after a LTO final link,
    but I haven't gotten around to port that one.

    It seems to work already for the single file modules.

    -Andi

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