[PATCH] kbuild: fix CONFIG_TRIM_UNUSED_KSYMS build for ppc64

[PATCH] kbuild: fix CONFIG_TRIM_UNUSED_KSYMS build for ppc64

[Masahiro Yamada]

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@canb.auug.org.au>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---

 scripts/gen_autoksyms.sh | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/scripts/gen_autoksyms.sh b/scripts/gen_autoksyms.sh
index 16c0b2ddaa4c..d54dfba15bf2 100755
--- a/scripts/gen_autoksyms.sh
+++ b/scripts/gen_autoksyms.sh
@@ -43,6 +43,9 @@ EOT
 sed 's/ko$/mod/' $modlist |
 xargs -n1 sed -n -e '2{s/ /\n/g;/^$/!p;}' -- |
 cat - "$ksym_wl" |
+# Remove the dot prefix for ppc64; symbol names with a dot (.) hold entry
+# point addresses.
+sed -e 's/^\.//' |
 sort -u |
 sed -e 's/\(.*\)/#define __KSYM_\1 1/' >> "$output_file"
 
-- 
2.27.0

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@canb.auug.org.au/
>Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
>Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

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

    Tested-by: Jessica Yu <jeyu@kernel.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

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

[Masahiro Yamada]

On Thu, Feb 11, 2021 at 7:43 PM Jessica Yu <jeyu@kernel.org> wrote:
>
> +++ 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@canb.auug.org.au>
> >Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
>
> Thanks a lot for the quick fix. This fixes the ppc64 build issue on my end:
>
>     Tested-by: Jessica Yu <jeyu@kernel.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


Applied to linux-kbuild/fixes.


-- 
Best Regards
Masahiro Yamada