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    SubjectRe: [PATCH v8 00/16] Add support for Clang LTO
    On Tue, Dec 8, 2020 at 1:15 PM Arnd Bergmann <arnd@kernel.org> wrote:
    >
    > - one build seems to have dropped all symbols the string operations
    > from vmlinux,
    > so while the link goes through, modules cannot be loaded:
    > ERROR: modpost: "memmove" [drivers/media/rc/rc-core.ko] undefined!
    > ERROR: modpost: "memcpy" [net/wireless/cfg80211.ko] undefined!
    > ERROR: modpost: "memcpy" [net/8021q/8021q.ko] undefined!
    > ERROR: modpost: "memset" [net/8021q/8021q.ko] undefined!
    > ERROR: modpost: "memcpy" [net/unix/unix.ko] undefined!
    > ERROR: modpost: "memset" [net/sched/cls_u32.ko] undefined!
    > ERROR: modpost: "memcpy" [net/sched/cls_u32.ko] undefined!
    > ERROR: modpost: "memset" [net/sched/sch_skbprio.ko] undefined!
    > ERROR: modpost: "memcpy" [net/802/garp.ko] undefined!
    > I first thought this was related to a clang-12 bug I saw the other day, but
    > this also happens with clang-11

    It seems to happen because of CONFIG_TRIM_UNUSED_KSYMS,
    which is a shame, since I think that is an option we'd always want to
    have enabled with LTO, to allow more dead code to be eliminated.

    Arnd

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