Re: [PATCH v2 2/2] kbuild: lto: preserve MAKEFLAGS for module linking

[Jiri Slaby]

On 19. 07. 22, 11:15, Masahiro Yamada wrote:
> On Tue, Jul 19, 2022 at 5:41 PM Jiri Slaby <jslaby@xxxxxxx> wrote:
> > From: Martin Liska <mliska@xxxxxxx>
> >
> > Prefix command in makefile run in order to preserve access to jobserver.
> > This is needed for gcc at least.
> >
> > Fixes this warning:
> > lto-wrapper: warning: jobserver is not available: ‘--jobserver-auth=’ is not present in ‘MAKEFLAGS’
>
>
> What is lto-wrapper ?

lto-wrapper is a part of gcc:
https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/lto-wrapper.cc

And is invoked during the link of LTO objects (also to link in parallel 
if jobserver is available).

I am leaving the unanswered questions below for Martin to answer.

> > Cc: Sedat Dilek <sedat.dilek@xxxxxxxxx>
> > Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> > Cc: Michal Marek <michal.lkml@xxxxxxxxxxx>
> > Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> > Fixes: 5d45950dfbb1 (kbuild: move vmlinux.o link to scripts/Makefile.vmlinux_o)
> > Signed-off-by: Martin Liska <mliska@xxxxxxx>
> > Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
> > ---
> >
> > Notes:
> >      [v2] this is new in v2
> >
> >   scripts/Makefile.build | 6 +++---
> >   1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> > index bb63374fb055..493f3c4e8461 100644
> > --- a/scripts/Makefile.build
> > +++ b/scripts/Makefile.build
> > @@ -247,8 +247,8 @@ endef
> >
> >   # Built-in and composite module parts
> >   $(obj)/%.o: $(src)/%.c $(recordmcount_source) FORCE
> > -       $(call if_changed_rule,cc_o_c)
> > -       $(call cmd,force_checksrc)
> > +       +$(call if_changed_rule,cc_o_c)
> > +       +$(call cmd,force_checksrc)
>
>
> cmd_force_checksrc invokes sparse.
> How is it related to GCC?
>
>
>
>
> >   # To make this rule robust against "Argument list too long" error,
> >   # ensure to add $(obj)/ prefix by a shell command.
> > @@ -457,7 +457,7 @@ endef
> >   $(multi-obj-m): objtool-enabled := $(delay-objtool)
> >   $(multi-obj-m): part-of-module := y
> >   $(multi-obj-m): %.o: %.mod FORCE
> > -       $(call if_changed_rule,ld_multi_m)
> > +       +$(call if_changed_rule,ld_multi_m)
> >   $(call multi_depend, $(multi-obj-m), .o, -objs -y -m)
>
>
> cmd_ld_multi_m invokes $(LD) directly.
> How is it related to gcc?



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