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SubjectRe: [PATCH] kbuild: reuse vmlinux.o in vmlinux_link
On Thu, May 21, 2020 at 01:27:16PM -0700, Sami Tolvanen 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).

Nice! Any time savings at final link is a big cumulative win.

> 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} \

I think the "um" case can be updated as well too, yes?

Also, I think the comment above modpost_link() needs to be updated now
to reflect the nature of how vmlinux.o gets used after this patch.

--
Kees Cook

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