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

[Sasha Levin <sashal@kernel.org>]

On Tue, Oct 13, 2026 at 10:38:37PM +0200, Thomas Weißschuh wrote:
>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?

Building with ARCH=um was reaching the tools, which then set "-I
tools/arch/um/include" but that dir doesn't exist.

I worked around this for the RFC, but I think I can address it when I resent
the patches.

>> +	depends on TOOLS_BUILD_ABI && TOOLS_BUILD_GLIBC
>
>These dependencies could be on separate lines, it will reduce churn when
>they get modified.

ack

>> +	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.

I originally added this because perf was silly, but apparently that was a bug
instead of intended behavior, which was fixed in 5479e1a13b759 ("perf tools:
Put Python bytecode in output directory"), so I think I can just drop this
altogether.

-- 
Thanks,
Sasha