Re: [PATCH] kbuild: fix CONFIG_TRIM_UNUSED_KSYMS build for ppc64

[Jessica Yu]

+++ 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@xxxxxxxxxxxxxxxx/
> Reported-by: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
> Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>

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

   Tested-by: Jessica Yu <jeyu@xxxxxxxxxx>

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