Re: [PATCH] kbuild: reuse vmlinux.o in vmlinux_link

From: Masahiro Yamada <masahiroy@kernel.org>
To: Sami Tolvanen <samitolvanen@google.com>
Cc: Michal Marek <michal.lkml@markovi.net>,
	Kees Cook <keescook@chromium.org>,
	Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] kbuild: reuse vmlinux.o in vmlinux_link
Date: Sat, 23 May 2020 02:41:42 +0900	[thread overview]
Message-ID: <CAK7LNARq3g5vA6vy9449SHsKQmbwJrQDSBz4ZbH1pBEvPmusuA@mail.gmail.com> (raw)
In-Reply-To: <20200521202716.193316-1-samitolvanen@google.com>

On Fri, May 22, 2020 at 5:27 AM Sami Tolvanen <samitolvanen@google.com> wrote:
>
> Instead of linking all compilation units again each time vmlinux_link is
> called, reuse vmlinux.o from modpost_link.
>
> With x86_64 allyesconfig, vmlinux_link is called three times and reusing
> vmlinux.o reduces the build time ~38 seconds on my system (59% reduction
> in the time spent in vmlinux_link).
>
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> ---
>  scripts/link-vmlinux.sh | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index d09ab4afbda4..c6cc4305950c 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -77,11 +77,8 @@ vmlinux_link()
>
>         if [ "${SRCARCH}" != "um" ]; then
>                 objects="--whole-archive                        \
> -                       ${KBUILD_VMLINUX_OBJS}                  \
> +                       vmlinux.o                               \
>                         --no-whole-archive                      \
> -                       --start-group                           \
> -                       ${KBUILD_VMLINUX_LIBS}                  \
> -                       --end-group                             \
>                         ${@}"
>
>                 ${LD} ${KBUILD_LDFLAGS} ${LDFLAGS_vmlinux}      \
>
> base-commit: b85051e755b0e9d6dd8f17ef1da083851b83287d
> --
> 2.27.0.rc0.183.gde8f92d652-goog
>

I like this patch irrespective of CLANG_LTO, but
unfortunately, my build test failed.

ARCH=powerpc failed to build as follows:

  MODPOST vmlinux.o
  MODINFO modules.builtin.modinfo
  GEN     modules.builtin
  LD      .tmp_vmlinux.kallsyms1
vmlinux.o:(__ftr_alt_97+0x20): relocation truncated to fit:
R_PPC64_REL14 against `.text'+4b1c
vmlinux.o:(__ftr_alt_97+0x164): relocation truncated to fit:
R_PPC64_REL14 against `.text'+1cf78
vmlinux.o:(__ftr_alt_97+0x288): relocation truncated to fit:
R_PPC64_REL14 against `.text'+1dac4
vmlinux.o:(__ftr_alt_97+0x2f0): relocation truncated to fit:
R_PPC64_REL14 against `.text'+1e254
make: *** [Makefile:1125: vmlinux] Error 1

I used powerpc-linux-gcc
available at
https://mirrors.edge.kernel.org/pub/tools/crosstool/files/bin/x86_64/9.2.0/

Build command:

make -j24 ARCH=powerpc  CROSS_COMPILE=powerpc-linux-  defconfig all

Could you check it please?

I will apply it to my test branch.
Perhaps, 0-day bot may find more failure cases.

--
Best Regards
Masahiro Yamada