linux-kernel - Re: [PATCH] kbuild: Fix 'no symbols' warning when CONFIG_TRIM_UNUSD

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Message-ID: <CAFP8O3JtOpb368h4PBbYnR4fsqRYkX_TKuCKrS-Csu=dMMNiKA@mail.gmail.com>
Date:   Sat, 14 Aug 2021 20:18:31 -0700
From:   Fāng-ruì Sòng <maskray@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org,
        Nathan Chancellor <nathan@...nel.org>,
        linux-kernel@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Pitre <nico@...xnic.net>,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH] kbuild: Fix 'no symbols' warning when CONFIG_TRIM_UNUSD_KSYMS=y

On Sat, Aug 14, 2021 at 6:15 PM Nathan Chancellor <nathan@...nel.org> wrote:
>
> On 8/14/2021 4:41 PM, Masahiro Yamada wrote:
> > When CONFIG_TRIM_UNUSED_KSYMS is enabled, I see some warnings like this:
> >
> >    nm: arch/x86/entry/vdso/vdso32/note.o: no symbols
> >
> > $NM (both GNU nm and llvm-nm) warns when no symbol is found in the
> > object. Suppress the stderr.
> >
> > Fixes: bbda5ec671d3 ("kbuild: simplify dependency generation for CONFIG_TRIM_UNUSED_KSYMS")
> > Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>

LGTM.

FWIW binutils>=2.37 `nm -q` can be used to suppress "no symbols"
https://sourceware.org/bugzilla/show_bug.cgi?id=27408

llvm-nm>=13.0.0 supports -q as well.

> Reviewed-by: Nathan Chancellor <nathan@...nel.org>
>
> > ---
> >
> >   scripts/gen_ksymdeps.sh | 5 ++++-
> >   1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/scripts/gen_ksymdeps.sh b/scripts/gen_ksymdeps.sh
> > index 1324986e1362..5493124e8ee6 100755
> > --- a/scripts/gen_ksymdeps.sh
> > +++ b/scripts/gen_ksymdeps.sh
> > @@ -4,7 +4,10 @@
> >   set -e
> >
> >   # List of exported symbols
> > -ksyms=$($NM $1 | sed -n 's/.*__ksym_marker_\(.*\)/\1/p' | tr A-Z a-z)
> > +#
> > +# If the object has no symbol, $NM warns 'no symbols'.
> > +# Suppress the stdout.
> > +ksyms=$($NM $1 2>/dev/null | sed -n 's/.*__ksym_marker_\(.*\)/\1/p' | tr A-Z a-z)
> >
> >   if [ -z "$ksyms" ]; then
> >       exit 0
> >
>
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