Re: [RFC PATCH 2/6] kbuild: add "make tools_build" to build userspace tools from tools/

["Thomas Weißschuh" <thomas@t-8ch.de>]

On 2026-10-11 19:36:41-0400, Sasha Levin wrote:
(...)

> Assisted-by: LLM
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
>  .gitignore            |  5 +++
>  Makefile              |  8 ++++-
>  lib/Kconfig.debug     |  2 ++
>  tools/Kconfig         | 72 +++++++++++++++++++++++++++++++++++++++
>  tools/Makefile.kbuild | 79 +++++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 165 insertions(+), 1 deletion(-)
>  create mode 100644 tools/Kconfig
>  create mode 100644 tools/Makefile.kbuild

(...)

> diff --git a/tools/Kconfig b/tools/Kconfig
> new file mode 100644
> index 0000000000000..bf0643b39b86e
> --- /dev/null
> +++ b/tools/Kconfig
> @@ -0,0 +1,72 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +
> +config TOOLS_BUILD_ABI
> +	def_bool X86_64 || ARM64
> +
> +config TOOLS_BUILD_GLIBC
> +	def_bool $(success,echo '#include <features.h>' | $(CC) $(CLANG_FLAGS) $(USERCFLAGS) -E -dM -x c - | grep -q __GLIBC__)
> +
> +menuconfig TOOLS_BUILD
> +	bool "Build userspace tools from tools/"
> +	depends on CC_CAN_LINK && !UML

Why !UML?

> +	depends on TOOLS_BUILD_ABI && TOOLS_BUILD_GLIBC

These dependencies could be on separate lines, it will reduce churn when
they get modified.

> +	help
> +	  Build the selected programs under tools/ for the target together
> +	  with the kernel, as part of "make all", or alone with
> +	  "make tools_build". Each program is built by its own build system
> +	  into tools-build/ in the object tree. The tools then always match
> +	  the kernel they were built with, and a change that breaks one of
> +	  them shows up in the same build that compiles the kernel.
> +
> +	  This needs a compiler that can link glibc programs for the target,
> +	  and is currently limited to x86_64 and arm64.
> +
> +	  If unsure, say N.

(...)

> diff --git a/tools/Makefile.kbuild b/tools/Makefile.kbuild
> new file mode 100644
> index 0000000000000..820a2d9a3893b
> --- /dev/null
> +++ b/tools/Makefile.kbuild
> @@ -0,0 +1,79 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +#
> +# Builds the userspace programs selected in tools/Kconfig for the target.
> +# Invoked by "make tools_build", which "make all" runs when CONFIG_TOOLS_BUILD
> +# is set. Each program is built by its own build system, the way it is built
> +# standalone, into $(objtree)/tools-build/.
> +
> +PHONY := __tools_build
> +__tools_build:
> +
> +include include/config/auto.conf
> +
> +abs_srctree := $(realpath $(srctree))
> +toolsdir := $(abs_srctree)/tools
> +outdir := $(CURDIR)/tools-build
> +
> +# kbuild's state and the user's compiler flags, from the environment or the
> +# command line, would change how these build
> +unexport srctree objtree srcroot VPATH building_out_of_srctree sub_make_done
> +unexport CLANG_FLAGS INSTALL_HDR_PATH O
> +unexport CFLAGS CPPFLAGS LDFLAGS EXTRA_CFLAGS EXTRA_LDFLAGS USERCFLAGS USERLDFLAGS
> +space := $(subst ,, )
> +overrides := $(subst \$(space),\@space@,$(MAKEOVERRIDES))
> +MAKEOVERRIDES := $(subst \@space@,\$(space),$(filter-out O=% CFLAGS=% CPPFLAGS=% \
> +	LDFLAGS=% EXTRA_CFLAGS=% EXTRA_LDFLAGS=% USERCFLAGS=% USERLDFLAGS=%,$(overrides)))
> +
> +# Keep Python's bytecode caches out of the source tree
> +export PYTHONDONTWRITEBYTECODE := 1

This should just be done in the toplevel Makefile IMO.

> +# The compiler CONFIG_CC_CAN_LINK was tested with. The tools take linker
> +# flags from LDFLAGS.
> +tools-cc := $(CC) $(USERCFLAGS) $(KBUILD_USERABI)
> +ifneq ($(USERLDFLAGS),)
> +override LDFLAGS := $(USERLDFLAGS)
> +export LDFLAGS
> +endif

(...)