linux-kernel - Re: [PATCH 1/2] kbuild: set y instead of 1 to KBUILD

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Message-ID: <20250602220431.GA924363@ax162>
Date: Mon, 2 Jun 2025 15:04:31 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Masahiro Yamada <masahiroy@...nel.org>
Cc: linux-kbuild@...r.kernel.org, Jonathan Corbet <corbet@....net>,
	Nicolas Schier <nicolas.schier@...ux.dev>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] kbuild: set y instead of 1 to
 KBUILD_{BUILTIN,MODULES}

On Tue, Jun 03, 2025 at 03:12:53AM +0900, Masahiro Yamada wrote:
> KBUILD_BUILTIN is set to 1 unless you are building only modules.
> 
> KBUILT_MODULES is set to 1 when you are building only modules
> (a typical use case is "make modules").
> 
> It is more useful to set them to 'y' instead, so we can do
> something like:
> 
>     always-$(KBUILD_BUILTIN) += vmlinux.lds
> 
> This works equivalently to:
> 
>     extra-y                  += vmlinux.lds
> 
> This allows us to deprecate extra-y. extra-y and always-y are quite
> similar, and we do not need both.
> 
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>

Reviewed-by: Nathan Chancellor <nathan@...nel.org>

> ---
> 
>  Documentation/kbuild/makefiles.rst |  8 ++++++--
>  Makefile                           | 16 ++++++++--------
>  2 files changed, 14 insertions(+), 10 deletions(-)
> 
> diff --git a/Documentation/kbuild/makefiles.rst b/Documentation/kbuild/makefiles.rst
> index 3b9a8bc671e2..264b83182509 100644
> --- a/Documentation/kbuild/makefiles.rst
> +++ b/Documentation/kbuild/makefiles.rst
> @@ -273,8 +273,8 @@ It is good practice to use a ``CONFIG_`` variable when assigning directory
>  names. This allows kbuild to totally skip the directory if the
>  corresponding ``CONFIG_`` option is neither "y" nor "m".
>  
> -Non-builtin vmlinux targets - extra-y
> --------------------------------------
> +Non-builtin vmlinux targets - extra-y (DEPRECATED)
> +--------------------------------------------------
>  
>  extra-y specifies targets which are needed for building vmlinux,
>  but not combined into built-in.a.
> @@ -291,6 +291,10 @@ Example::
>    # arch/x86/kernel/Makefile
>    extra-y	+= vmlinux.lds
>  
> +extra-y is now deprecated because this is equivalent to:
> +
> +  always-$(KBUILD_BUILTIN) += vmlinux.lds
> +
>  $(extra-y) should only contain targets needed for vmlinux.
>  
>  Kbuild skips extra-y when vmlinux is apparently not a final goal.
> diff --git a/Makefile b/Makefile
> index 7a52be3a4b80..72e75a0caa32 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -749,7 +749,7 @@ targets :=
>  # Normally, just do built-in.
>  
>  KBUILD_MODULES :=
> -KBUILD_BUILTIN := 1
> +KBUILD_BUILTIN := y
>  
>  # If we have only "make modules", don't compile built-in objects.
>  ifeq ($(MAKECMDGOALS),modules)
> @@ -761,11 +761,11 @@ endif
>  # Just "make" or "make all" shall build modules as well
>  
>  ifneq ($(filter all modules nsdeps compile_commands.json clang-%,$(MAKECMDGOALS)),)
> -  KBUILD_MODULES := 1
> +  KBUILD_MODULES := y
>  endif
>  
>  ifeq ($(MAKECMDGOALS),)
> -  KBUILD_MODULES := 1
> +  KBUILD_MODULES := y
>  endif
>  
>  export KBUILD_MODULES KBUILD_BUILTIN
> @@ -1193,7 +1193,7 @@ export KBUILD_LDS          := arch/$(SRCARCH)/kernel/vmlinux.lds
>  ifdef CONFIG_TRIM_UNUSED_KSYMS
>  # For the kernel to actually contain only the needed exported symbols,
>  # we have to build modules as well to determine what those symbols are.
> -KBUILD_MODULES := 1
> +KBUILD_MODULES := y
>  endif
>  
>  PHONY += vmlinux_a
> @@ -1529,7 +1529,7 @@ all: modules
>  # the built-in objects during the descend as well, in order to
>  # make sure the checksums are up to date before we record them.
>  ifdef CONFIG_MODVERSIONS
> -  KBUILD_BUILTIN := 1
> +  KBUILD_BUILTIN := y
>  endif
>  
>  # Build modules
> @@ -1538,7 +1538,7 @@ endif
>  # *.ko are usually independent of vmlinux, but CONFIG_DEBUG_INFO_BTF_MODULES
>  # is an exception.
>  ifdef CONFIG_DEBUG_INFO_BTF_MODULES
> -KBUILD_BUILTIN := 1
> +KBUILD_BUILTIN := y
>  modules: vmlinux
>  endif
>  
> @@ -1855,7 +1855,7 @@ filechk_kernel.release = echo $(KERNELRELEASE)
>  
>  # We are always building only modules.
>  KBUILD_BUILTIN :=
> -KBUILD_MODULES := 1
> +KBUILD_MODULES := y
>  
>  build-dir := .
>  
> @@ -1983,7 +1983,7 @@ endif
>  
>  single-goals := $(addprefix $(build-dir)/, $(single-no-ko))
>  
> -KBUILD_MODULES := 1
> +KBUILD_MODULES := y
>  
>  endif
>  
> -- 
> 2.43.0
>