linux-kernel - Re: [PATCH 4/4] kbuild: include Makefile.compiler only when compiler is required

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Date:   Thu, 18 Mar 2021 14:13:56 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Michal Marek <michal.lkml@...kovi.net>
Subject: Re: [PATCH 4/4] kbuild: include Makefile.compiler only when compiler
 is required

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@...nel.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