linux-kernel - Re: [PATCH mips-next 2/4] MIPS: vmlinux.lds.S: add ".rel.dyn" to DISCARDS

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Date:   Mon, 4 Jan 2021 23:39:32 -0800
From:   Fāng-ruì Sòng <maskray@...gle.com>
To:     Alexander Lobakin <alobakin@...me>
Cc:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Kees Cook <keescook@...omium.org>,
        Ingo Molnar <mingo@...nel.org>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Alex Smith <alex.smith@...tec.com>,
        Markos Chandras <markos.chandras@...tec.com>,
        linux-mips <linux-mips@...r.kernel.org>,
        "# 3.4.x" <stable@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH mips-next 2/4] MIPS: vmlinux.lds.S: add ".rel.dyn" to DISCARDS

On Mon, Jan 4, 2021 at 4:21 AM Alexander Lobakin <alobakin@...me> wrote:
>
> GCC somehow manages to place some of the symbols from main.c into
> .rel.dyn section:
>
> mips-alpine-linux-musl-ld: warning: orphan section `.rel.dyn'
> from `init/main.o' being placed in section `.rel.dyn'
>
> I couldn't catch up the exact symbol, but seems like it's harmless
> to discard it from the final vmlinux as kernel doesn't use or
> support dynamic relocations.
>
> Misc: sort DISCARDS section entries alphabetically.
>
> Signed-off-by: Alexander Lobakin <alobakin@...me>
> ---
>  arch/mips/kernel/vmlinux.lds.S | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S
> index 83e27a181206..1c3c2e903062 100644
> --- a/arch/mips/kernel/vmlinux.lds.S
> +++ b/arch/mips/kernel/vmlinux.lds.S
> @@ -221,9 +221,10 @@ SECTIONS
>                 /* ABI crap starts here */
>                 *(.MIPS.abiflags)
>                 *(.MIPS.options)
> +               *(.eh_frame)
>                 *(.options)
>                 *(.pdr)
>                 *(.reginfo)
> -               *(.eh_frame)
> +               *(.rel.dyn)
>         }
>  }
> --
> 2.30.0
>
>

(I don't know why I am on the CC list since I know little about
mips... Anyway, I know the LLD linker's behavior in case that was the
intention... )

I think it'd be good to know the reason why these dynamic relocations
are produced and fix the root cause.

arch/x86/kernel/vmlinux.lds.S asserts no dynamic relocation:
ASSERT(SIZEOF(.rela.dyn) == 0, "Unexpected run-time relocations
(.rela) detected!")