Re: [PATCH 09/13] kbuild: do not create built-in.a.symversions or lib.a.symversions

Kees Cook
2021-08-19T06:41:24Z

On Thu, Aug 19, 2021 at 09:57:40AM +0900, Masahiro Yamada wrote:
> Merge all *.o.symversions in scripts/link-vmlinux.sh instead of
> merging them in the unit of built-in.a or lib.a.
>
> This is a preparation for further code cleanups.

Looks good, though I wonder about this becoming serialized during the
link phase rather than doing the work per-target. I mean, it always had
to collect them all during the link phase (with "cat"), but before it
wasn't running $(AR) serially to do it.

I'll ponder how this might be made a little more parallel. But for now:

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

-Kees

>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> ---
>
> scripts/Makefile.build | 10 ++--------
> scripts/link-vmlinux.sh | 22 ++++++++++++++++++----
> 2 files changed, 20 insertions(+), 12 deletions(-)
>
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 585dae34746a..37d6f6da34d6 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -430,11 +430,8 @@ endif
> quiet_cmd_ar_builtin = AR $@
> cmd_ar_builtin = rm -f $@; $(AR) cDPrST $@ $(real-prereqs)
>
> -quiet_cmd_ar_and_symver = AR $@
> - cmd_ar_and_symver = $(cmd_update_lto_symversions); $(cmd_ar_builtin)
> -
> $(obj)/built-in.a: $(real-obj-y) FORCE
> - $(call if_changed,ar_and_symver)
> + $(call if_changed,ar_builtin)
>
> #
> # Rule to create modules.order file
> @@ -454,11 +451,8 @@ $(obj)/modules.order: $(obj-m) FORCE
> #
> # Rule to compile a set of .o files into one .a file (with symbol table)
> #
> -quiet_cmd_ar_lib = AR $@
> - cmd_ar_lib = $(cmd_update_lto_symversions); $(cmd_ar)
> -
> $(obj)/lib.a: $(lib-y) FORCE
> - $(call if_changed,ar_lib)
> + $(call if_changed,ar)
>
> # NOTE:
> # Do not replace $(filter %.o,^) with $(real-prereqs). When a single object
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index d74cee5c4326..17976609c2d8 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -52,6 +52,13 @@ gen_initcalls()
> > .tmp_initcalls.lds
> }
>
> +append_symversion()
> +{
> + if [ -f ${1}.symversions ]; then
> + cat ${1}.symversions >> .tmp_symversions.lds
> + fi
> +}
> +
> # If CONFIG_LTO_CLANG is selected, collect generated symbol versions into
> # .tmp_symversions.lds
> gen_symversions()
> @@ -59,10 +66,17 @@ gen_symversions()
> info GEN .tmp_symversions.lds
> rm -f .tmp_symversions.lds
>
> - for o in ${KBUILD_VMLINUX_OBJS} ${KBUILD_VMLINUX_LIBS}; do
> - if [ -f ${o}.symversions ]; then
> - cat ${o}.symversions >> .tmp_symversions.lds
> - fi
> + for a in ${KBUILD_VMLINUX_OBJS} ${KBUILD_VMLINUX_LIBS}; do
> + case $a in
> + *.a)
> + for o in $(${AR} t ${a}); do
> + append_symversion ${o}
> + done
> + ;;
> + *)
> + append_symversion ${a}
> + ;;
> + esac
> done
> }
>
> --
> 2.30.2
>

--
Kees Cook