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

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Date:   Wed, 18 Aug 2021 23:41:18 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org,
        Sami Tolvanen <samitolvanen@...gle.com>,
        linux-kernel@...r.kernel.org,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH 09/13] kbuild: do not create built-in.a.symversions or
 lib.a.symversions

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@...omium.org>

-Kees

> 
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.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