Re: [PATCH v2 3/5] kbuild: add read-file macro

[Nicolas Schier]

On Thu 24 Nov 2022 00:18:26 GMT, Masahiro Yamada wrote:
> Since GMU Make 4.2, $(file ...) supports the read operater '<', which is
> useful to read a file without forking any process. No warning is shown even
> if the input file is missing.
> 
> For older Make versions, it falls back to the cat command.
> 
> Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> ---
> 
> (no changes since v1)
> 
>  Makefile                  |  2 +-
>  scripts/Kbuild.include    | 12 ++++++++++++
>  scripts/Makefile.modfinal |  2 +-
>  scripts/Makefile.modinst  |  2 +-
>  4 files changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index eb80332f7b51..60ce9dcafc72 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -369,7 +369,7 @@ else # !mixed-build
>  include $(srctree)/scripts/Kbuild.include
>  
>  # Read KERNELRELEASE from include/config/kernel.release (if it exists)
> -KERNELRELEASE = $(shell cat include/config/kernel.release 2> /dev/null)
> +KERNELRELEASE = $(call read-file, include/config/kernel.release)
>  KERNELVERSION = $(VERSION)$(if $(PATCHLEVEL),.$(PATCHLEVEL)$(if $(SUBLEVEL),.$(SUBLEVEL)))$(EXTRAVERSION)
>  export VERSION PATCHLEVEL SUBLEVEL KERNELRELEASE KERNELVERSION
>  
> diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
> index 9996f34327cb..722846c23264 100644
> --- a/scripts/Kbuild.include
> +++ b/scripts/Kbuild.include
> @@ -10,6 +10,10 @@ empty   :=
>  space   := $(empty) $(empty)
>  space_escape := _-_SPACE_-_
>  pound := \#
> +define newline
> +
> +
> +endef
>  
>  ###
>  # Comparison macros.
> @@ -55,6 +59,14 @@ stringify = $(squote)$(quote)$1$(quote)$(squote)
>  kbuild-dir = $(if $(filter /%,$(src)),$(src),$(srctree)/$(src))
>  kbuild-file = $(or $(wildcard $(kbuild-dir)/Kbuild),$(kbuild-dir)/Makefile)
>  
> +###
> +# Read a file, replacing newlines with spaces
> +ifeq ($(call test-ge, $(MAKE_VERSION), 4.2),y)
> +read-file = $(subst $(newline),$(space),$(file < $1))
> +else
> +read-file = $(shell cat $1 2>/dev/null)
> +endif
> +

I like the implementation of read-file, but I am afraid that the 
MAKE_VERSION comparison breaks all make versions w/ a minor version 
number: 3.99.9x, 4.2.x, 4.3.x.

Not beautiful, but this might possibly work:
  ifneq ($(filter 3.% 4.0 4.0.% 4.1 4.1.%,$(MAKE_VERSION)),)
  read-file = ...


Kind regards,
Nicolas


>  ###
>  # Easy method for doing a status message
>         kecho := :
> diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
> index 25bedd83644b..7252f6cf7837 100644
> --- a/scripts/Makefile.modfinal
> +++ b/scripts/Makefile.modfinal
> @@ -13,7 +13,7 @@ include $(srctree)/scripts/Kbuild.include
>  include $(srctree)/scripts/Makefile.lib
>  
>  # find all modules listed in modules.order
> -modules := $(sort $(shell cat $(MODORDER)))
> +modules := $(sort $(call read-file, $(MODORDER)))
>  
>  __modfinal: $(modules)
>  	@:
> diff --git a/scripts/Makefile.modinst b/scripts/Makefile.modinst
> index a4c987c23750..509d424dbbd2 100644
> --- a/scripts/Makefile.modinst
> +++ b/scripts/Makefile.modinst
> @@ -9,7 +9,7 @@ __modinst:
>  include include/config/auto.conf
>  include $(srctree)/scripts/Kbuild.include
>  
> -modules := $(sort $(shell cat $(MODORDER)))
> +modules := $(sort $(call read-file, $(MODORDER)))
>  
>  ifeq ($(KBUILD_EXTMOD),)
>  dst := $(MODLIB)/kernel
> -- 
> 2.34.1

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