Re: [PATCH 06/13] kbuild: merge vmlinux_link() between the ordinary link and Clang LTO

Kees Cook
2021-08-19T02:42:22Z

On Thu, Aug 19, 2021 at 09:57:37AM +0900, Masahiro Yamada wrote:
> When Clang LTO is enabled, vmlinux_link() reuses vmlinux.o instead of
> linking ${KBUILD_VMLINUX_OBJS} and ${KBUILD_VMLINUX_LIBS} again.
>
> That is the only difference here, so merge the similar code.

Oh excellent! I had tried to get this merged before and was not happy
with anything I constructed. This is much cleaner. Nice! (I think I
didn't realize there could be an empty --start-group/--end-group with
no side-effects.)

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> ---
>
> scripts/link-vmlinux.sh | 30 ++++++++++++++----------------
> 1 file changed, 14 insertions(+), 16 deletions(-)
>
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index 36ef7b37fc5d..a6c4d0bce3ba 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -154,12 +154,23 @@ vmlinux_link()
> local objects
> local strip_debug
> local map_option
> + local objs
> + local libs
>
> info LD ${output}
>
> # skip output file argument
> shift
>
> + if [ -n "${CONFIG_LTO_CLANG}" ]; then
> + # Use vmlinux.o instead of performing the slow LTO link again.
> + objs=vmlinux.o
> + libs=
> + else
> + objs="${KBUILD_VMLINUX_OBJS}"
> + libs="${KBUILD_VMLINUX_LIBS}"
> + fi
> +
> # The kallsyms linking does not need debug symbols included.
> if [ "$output" != "${output#.tmp_vmlinux.kallsyms}" ] ; then
> strip_debug=-Wl,--strip-debug
> @@ -170,22 +181,9 @@ vmlinux_link()
> fi
>
> if [ "${SRCARCH}" != "um" ]; then
> - if [ -n "${CONFIG_LTO_CLANG}" ]; then
> - # Use vmlinux.o instead of performing the slow LTO
> - # link again.
> - objects="--whole-archive \
> - vmlinux.o \
> - --no-whole-archive \
> - ${@}"
> - else
> - objects="--whole-archive \
> - ${KBUILD_VMLINUX_OBJS} \
> - --no-whole-archive \
> - --start-group \
> - ${KBUILD_VMLINUX_LIBS} \
> - --end-group \
> - ${@}"
> - fi
> + objects="--whole-archive ${objs} --no-whole-archive \
> + --start-group ${libs} --end-group \
> + $@"
>
> ${LD} ${KBUILD_LDFLAGS} ${LDFLAGS_vmlinux} \
> ${strip_debug#-Wl,} \
> --
> 2.30.2
>

--
Kees Cook