linux-kernel - Re: [PATCH] kallsyms: fix nonconverging kallsyms table with lld

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Date:   Fri, 5 Feb 2021 17:41:05 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Arnd Bergmann <arnd@...db.de>,
        David Brazdil <dbrazdil@...gle.com>,
        Marc Zyngier <maz@...nel.org>,
        Mikhail Petrov <Mikhail.Petrov@....dev>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kallsyms: fix nonconverging kallsyms table with lld

On Fri, Feb 5, 2021 at 12:30 AM Arnd Bergmann <arnd@...nel.org> wrote:
>
> From: Arnd Bergmann <arnd@...db.de>
>
> ARM randconfig builds with lld sometimes show a build failure
> from kallsyms:
>
>   Inconsistent kallsyms data
>   Try make KALLSYMS_EXTRA_PASS=1 as a workaround
>
> The problem is the veneers/thunks getting added by the linker extend
> the symbol table, which in turn leads to more veneers being needed,
> so it may take a few extra iterations to converge.
>
> This bug has been fixed multiple times before, but comes back every time
> a new symbol name is used. lld uses a different set of idenitifiers from
> ld.bfd, so the additional ones need to be added as well.

Yes, this is a whack-a-mole.

I fixed the typo "idenitifiers" -> "identifiers"
and applied to linux-kbuild.

Thanks.




> I looked through the sources and found that arm64 and mips define similar
> prefixes, so I'm adding those as well, aside from the ones I observed. I'm
> not sure about powerpc64, which seems to already be handled through a
> section match, but if it comes back, the "__long_branch_" and "__plt_"
> prefixes would have to get added as well.
>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  scripts/kallsyms.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
> index 7ecd2ccba531..54ad86d13784 100644
> --- a/scripts/kallsyms.c
> +++ b/scripts/kallsyms.c
> @@ -112,6 +112,12 @@ static bool is_ignored_symbol(const char *name, char type)
>                 "__crc_",               /* modversions */
>                 "__efistub_",           /* arm64 EFI stub namespace */
>                 "__kvm_nvhe_",          /* arm64 non-VHE KVM namespace */
> +               "__AArch64ADRPThunk_",  /* arm64 lld */
> +               "__ARMV5PILongThunk_",  /* arm lld */
> +               "__ARMV7PILongThunk_",
> +               "__ThumbV7PILongThunk_",
> +               "__LA25Thunk_",         /* mips lld */
> +               "__microLA25Thunk_",
>                 NULL
>         };
>
> --
> 2.29.2
>


-- 
Best Regards
Masahiro Yamada