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    SubjectRe: [PATCH v6 13/29] arm64/build: Assert for unwanted sections
    Hi Nick,

    CC Josh

    On Mon, Oct 26, 2020 at 6:49 PM Nick Desaulniers
    <ndesaulniers@google.com> wrote:
    > On Mon, Oct 26, 2020 at 10:44 AM Geert Uytterhoeven
    > <geert@linux-m68k.org> wrote:
    > > On Mon, Oct 26, 2020 at 6:39 PM Ard Biesheuvel <ardb@kernel.org> wrote:
    > > > On Mon, 26 Oct 2020 at 17:01, Geert Uytterhoeven <geert@linux-m68k.org> wrote:
    > > > > On Mon, Oct 26, 2020 at 2:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
    > > > > > On Mon, Oct 26, 2020 at 1:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
    > > > > > > On Fri, Aug 21, 2020 at 9:56 PM Kees Cook <keescook@chromium.org> wrote:
    > > > > > > > In preparation for warning on orphan sections, discard
    > > > > > > > unwanted non-zero-sized generated sections, and enforce other
    > > > > > > > expected-to-be-zero-sized sections (since discarding them might hide
    > > > > > > > problems with them suddenly gaining unexpected entries).
    > > > > > > >
    > > > > > > > Suggested-by: Ard Biesheuvel <ardb@kernel.org>
    > > > > > > > Signed-off-by: Kees Cook <keescook@chromium.org>
    > > > > > >
    > > > > > > This is now commit be2881824ae9eb92 ("arm64/build: Assert for unwanted
    > > > > > > sections") in v5.10-rc1, and is causing the following error with
    > > > > > > renesas_defconfig[1]:
    > > > > > >
    > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from
    > > > > > > `kernel/bpf/core.o' being placed in section `.eh_frame'
    > > > > > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected!
    > > > > > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected!
    > > > > > >
    > > > > > > I cannot reproduce this with the standard arm64 defconfig.
    > > > > > >
    > > > > > > I bisected the error to the aforementioned commit, but understand this
    > > > > > > is not the real reason. If I revert this commit, I still get:
    > > > > > >
    > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.got.plt' from
    > > > > > > `arch/arm64/kernel/head.o' being placed in section `.got.plt'
    > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.plt' from
    > > > > > > `arch/arm64/kernel/head.o' being placed in section `.plt'
    > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.data.rel.ro' from
    > > > > > > `arch/arm64/kernel/head.o' being placed in section `.data.rel.ro'
    > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from
    > > > > > > `kernel/bpf/core.o' being placed in section `.eh_frame'
    > > > > > >
    > > > > > > I.e. including the ".eh_frame" warning. I have tried bisecting that
    > > > > > > warning (i.e. with be2881824ae9eb92 reverted), but that leads me to
    > > > > > > commit b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section
    > > > > > > placement"), which is another red herring.
    > > > > >
    > > > > > kernel/bpf/core.o is the only file containing an eh_frame section,
    > > > > > causing the warning.
    >
    > When I see .eh_frame, I think -fno-asynchronous-unwind-tables is
    > missing from someone's KBUILD_CFLAGS.
    > But I don't see anything curious in kernel/bpf/Makefile, unless
    > cc-disable-warning is somehow broken.

    I tracked it down to kernel/bpf/core.c:___bpf_prog_run() being tagged
    with __no_fgcse aka __attribute__((optimize("-fno-gcse"))).

    Even if the function is trivially empty ("return 0;"), a ".eh_frame" section
    is generated. Removing the __no_fgcse tag fixes that.

    Gr{oetje,eeting}s,

    Geert

    --
    Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

    In personal conversations with technical people, I call myself a hacker. But
    when I'm talking to journalists I just say "programmer" or something like that.
    -- Linus Torvalds

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