[PATCH 4/4] kbuild: include Makefile.compiler only when compiler is required

[Masahiro Yamada]

(CC: Will and ARM ML)


On Fri, Mar 19, 2021 at 6:14 AM Nathan Chancellor <nathan at kernel.org> wrote:
>
> On Sun, Feb 28, 2021 at 03:10:28PM +0900, Masahiro Yamada wrote:
> > Since commit f2f02ebd8f38 ("kbuild: improve cc-option to clean up all
> > temporary files"), running 'make kernelversion' in a read-only source
> > tree emits a bunch of warnings:
> >
> >   mkdir: cannot create directory '.tmp_12345': Permission denied
> >
> > Non-build targets such as kernelversion, clean, help, etc. do not
> > need to evaluate $(call cc-option,) and friends. Do not include
> > Makefile.compiler so $(call cc-option,) becomes no-op.
> >
> > This not only fix the warnings, but also runs non-build targets much
> > faster.
> >
> > Basically, all installation targets should also be non-build targets.
> > Unfortunately, vdso_install requires the compiler because it builds
> > vdso before installtion. This is a problem that must be fixed by a
> > separate patch.
> >
> > Signed-off-by: Masahiro Yamada <masahiroy at kernel.org>
> > ---
> >
> > I am not adding Reported-by for now because a reporter sent me
> > an email privately.
> >
> > If he allows me to add Reported-by, I will add it to record
> > the credit.
> >
> > (Perhaps, another person might have reported a similar issue
> > somewhere, but my memory is obsure. I cannot recall it.)
> >
> >
> >  Makefile | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> >
> > diff --git a/Makefile b/Makefile
> > index eec7a94f5c33..20724711dc71 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -263,6 +263,10 @@ no-dot-config-targets := $(clean-targets) \
> >                        $(version_h) headers headers_% archheaders archscripts \
> >                        %asm-generic kernelversion %src-pkg dt_binding_check \
> >                        outputmakefile
> > +# Installation targets should not require compiler. Unfortunately, vdso_install
> > +# is an exception where build artifacts may be updated. This must be fixed.
> > +no-compiler-targets := $(no-dot-config-targets) install dtbs_install \
> > +                     headers_install modules_install kernelrelease image_name
> >  no-sync-config-targets := $(no-dot-config-targets) %install kernelrelease \
> >                         image_name
> >  single-targets := %.a %.i %.ko %.lds %.ll %.lst %.mod %.o %.s %.symtypes %/
> > @@ -270,6 +274,7 @@ single-targets := %.a %.i %.ko %.lds %.ll %.lst %.mod %.o %.s %.symtypes %/
> >  config-build :=
> >  mixed-build  :=
> >  need-config  := 1
> > +need-compiler        := 1
> >  may-sync-config      := 1
> >  single-build :=
> >
> > @@ -279,6 +284,12 @@ ifneq ($(filter $(no-dot-config-targets), $(MAKECMDGOALS)),)
> >       endif
> >  endif
> >
> > +ifneq ($(filter $(no-compiler-targets), $(MAKECMDGOALS)),)
> > +     ifeq ($(filter-out $(no-compiler-targets), $(MAKECMDGOALS)),)
> > +             need-compiler :=
> > +     endif
> > +endif
> > +
> >  ifneq ($(filter $(no-sync-config-targets), $(MAKECMDGOALS)),)
> >       ifeq ($(filter-out $(no-sync-config-targets), $(MAKECMDGOALS)),)
> >               may-sync-config :=
> > @@ -584,7 +595,9 @@ endif
> >
> >  # Include this also for config targets because some architectures need
> >  # cc-cross-prefix to determine CROSS_COMPILE.
> > +ifdef need-compiler
> >  include $(srctree)/scripts/Makefile.compiler
> > +endif
> >
> >  ifdef config-build
> >  # ===========================================================================
> > --
> > 2.27.0
> >
>
> Hi Masahiro,
>
> I see a new warning in my builds on arm64 now when running
> 'modules_install' or 'dtbs_install' because ld-option evaluates to
> nothing, which triggers the warning in arch/arm64/Makefile:
>
> $ make -skj"$(nproc)" \
> ARCH=arm64 \
> CROSS_COMPILE=aarch64-linux- \
> INSTALL_DTBS_PATH=rootfs \
> INSTALL_MOD_PATH=rootfs \
> O=build/arm64 \
> distclean defconfig all modules_install dtbs_install
> ...
> /home/nathan/cbl/src/linux-next/arch/arm64/Makefile:25: ld does not support --fix-cortex-a53-843419; kernel may be susceptible to erratum
> /home/nathan/cbl/src/linux-next/arch/arm64/Makefile:25: ld does not support --fix-cortex-a53-843419; kernel may be susceptible to erratum
>
> $ sed -n '23,29p' arch/arm64/Makefile
> ifeq ($(CONFIG_ARM64_ERRATUM_843419),y)
>   ifeq ($(call ld-option, --fix-cortex-a53-843419),)
> $(warning ld does not support --fix-cortex-a53-843419; kernel may be susceptible to erratum)
>   else
> LDFLAGS_vmlinux += --fix-cortex-a53-843419
>   endif
> endif
>
> I am not sure how this should be resolved, hence just the report.
>
> Cheers,
> Nathan


I see this a few lines below:

ifeq ($(CONFIG_ARM64_USE_LSE_ATOMICS), y)
  ifneq ($(CONFIG_ARM64_LSE_ATOMICS), y)
$(warning LSE atomics not supported by binutils)
  endif
endif


We can move ld-option evaluation to Kconfig.

ifeq ($(CONFIG_ARM64_ERRATUM_843419),y)
  ifneq ($(CONFIG_ARM64_LD_HAS_FIX_ERRATUM_843419,y))
$(warning ld does not support --fix-cortex-a53-843419; kernel may be
susceptible to erratum)
  else
LDFLAGS_vmlinux += --fix-cortex-a53-843419
  endif
endif


I do not know what CONFIG name is preferred.



-- 
Best Regards
Masahiro Yamada