linux-kernel - Re: [PATCH] kbuild: fix CONFIG_TRIM_UNUSED

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Date:   Thu, 11 Feb 2021 11:43:35 +0100
From:   Jessica Yu <jeyu@...nel.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kbuild: fix CONFIG_TRIM_UNUSED_KSYMS build for ppc64

+++ Masahiro Yamada [11/02/21 15:14 +0900]:
>Stephen Rothwell reported a build error on ppc64 when
>CONFIG_TRIM_UNUSED_KSYMS is enabled.
>
>Jessica Yu pointed out the cause of the error with the reference to the
>ppc64 elf ABI:
>  "Symbol names with a dot (.) prefix are reserved for holding entry
>   point addresses. The value of a symbol named ".FN", if it exists,
>   is the entry point of the function "FN".
>
>As it turned out, CONFIG_TRIM_UNUSED_KSYMS has never worked for ppc64,
>which has been unnoticed until recently because this option depends on
>!UNUSED_SYMBOLS hence is disabled by all{mod,yes}config. (Then, it was
>uncovered by another patch removing UNUSED_SYMBOLS.)
>
>Removing the dot prefix in scripts/gen_autoksyms.sh fixes the issue.
>Please note it must be done before 'sort -u', because modules have
>both ._mcount and _mcount undefined when CONFIG_FUNCTION_TRACER=y.
>
>Link: https://lore.kernel.org/lkml/20210209210843.3af66662@canb.auug.org.au/
>Reported-by: Stephen Rothwell <sfr@...b.auug.org.au>
>Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>

Thanks a lot for the quick fix. This fixes the ppc64 build issue on my end:

    Tested-by: Jessica Yu <jeyu@...nel.org>

Do you plan to take this through the kbuild tree? If so, please let me
know when you've applied it, then I can undo the temporary workaround
I currently have in modules-next.

Thank you!

Jessica