linux-kernel - Re: [PATCH] kbuild: pass jobserver to cmd_ld

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Date:   Thu, 16 Jun 2022 16:09:53 +0200
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Jiri Slaby <jslaby@...e.cz>
Cc:     masahiroy@...nel.org, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH] kbuild: pass jobserver to cmd_ld_vmlinux.o

On Thu, Jun 16, 2022 at 12:45 PM Jiri Slaby <jslaby@...e.cz> wrote:
>
> Until the link-vmlinux.sh split (cf. the commit below), the linker was
> run with jobserver set in MAKEFLAGS. After the split, the command in
> Makefile.vmlinux_o is not prefixed by "+" anymore, so this information
> is lost.
>
> Restore it as linkers working in parallel (esp. the LTO ones) make a use
> of it.
>
> Cc: Sedat Dilek <sedat.dilek@...il.com>
> Cc: Masahiro Yamada <masahiroy@...nel.org>
> Cc: Michal Marek <michal.lkml@...kovi.net>
> Cc: Nick Desaulniers <ndesaulniers@...gle.com>
> Fixes: 5d45950dfbb1 (kbuild: move vmlinux.o link to scripts/Makefile.vmlinux_o)
> Signed-off-by: Jiri Slaby <jslaby@...e.cz>

Nice catch.
( I have seen some slowdown in my build-time. Will test and report. )

Reviewed-by: Sedat Dilek <sedat.dilek@...il.com>

-Sedat-

> ---
>  scripts/Makefile.vmlinux_o | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/scripts/Makefile.vmlinux_o b/scripts/Makefile.vmlinux_o
> index 3c97a1564947..d032f625b576 100644
> --- a/scripts/Makefile.vmlinux_o
> +++ b/scripts/Makefile.vmlinux_o
> @@ -65,7 +65,7 @@ define rule_ld_vmlinux.o
>  endef
>
>  vmlinux.o: $(initcalls-lds) $(KBUILD_VMLINUX_OBJS) $(KBUILD_VMLINUX_LIBS) FORCE
> -       $(call if_changed_rule,ld_vmlinux.o)
> +       +$(call if_changed_rule,ld_vmlinux.o)
>
>  targets += vmlinux.o
>
> --
> 2.36.1
>