Re: [PATCH v3 2/7] kbuild: add "make tools_build" to build userspace tools from tools/

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [Low] kbuild: USERLDFLAGS in LDFLAGS is ignored when building tools/dma
- [Low] kbuild: missing $(m64-flag) in CONFIG_TOOLS_BUILD_GLIBC preprocessor probe
--

commit 73fb4c9163d06e31dd88981052867f3114563466
Author: Sasha Levin <sashal@kernel.org>

kbuild: add "make tools_build" to build userspace tools from tools/

This commit introduces a CONFIG_TOOLS_BUILD menu in tools/Kconfig and a
tools_build make target backed by tools/Makefile.kbuild to build selected
userspace tools for the target architecture into tools-build/.

> diff --git a/tools/Kconfig b/tools/Kconfig
> new file mode 100644
> index 0000000000000..2d05c8e593e21
> --- /dev/null
> +++ b/tools/Kconfig
> @@ -0,0 +1,73 @@
> +# 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__)

[Severity: Low]
Should this preprocessor probe also pass $(m64-flag)?

In scripts/Kconfig.toolchain, CC_CAN_LINK passes $(m64-flag) to
cc_can_link_user when 64BIT is enabled, and tools/Makefile.kbuild passes
$(KBUILD_USERABI) (which includes -m64 on x86_64) in tools-cc.

When configuring an x86_64 kernel with a biarch GCC toolchain that defaults
to 32-bit mode and only has 64-bit glibc development headers
(gnu/stubs-64.h) installed without 32-bit headers (gnu/stubs-32.h), running
$(CC) $(CLANG_FLAGS) $(USERCFLAGS) -E -dM -x c - without $(m64-flag)
preprocesses <features.h> in 32-bit mode. That fails with a fatal error on
the missing <gnu/stubs-32.h> before -dM outputs macro definitions, causing
TOOLS_BUILD_GLIBC to evaluate to n even though the compiler can build 64-bit
glibc programs for the target.

[ ... ]

> diff --git a/tools/Makefile.kbuild b/tools/Makefile.kbuild
> new file mode 100644
> index 0000000000000..8cfa7f80039cd
> --- /dev/null
> +++ b/tools/Makefile.kbuild
> @@ -0,0 +1,85 @@
[ ... ]
> +# 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

[Severity: Low]
Will USERLDFLAGS reach tools/dma when building with CONFIG_TOOLS_BUILD_DMA=y?

Here USERLDFLAGS is only passed through the exported LDFLAGS variable and is
not included in tools-cc. However, tools/dma/Makefile compiles and links
dma_map_benchmark in a single rule without referencing $(LDFLAGS):

tools/dma/Makefile:
$(OUTPUT)$(DMA_MAP_BENCHMARK): prepare FORCE
	$(CC) $(CFLAGS) $(DMA_MAP_BENCHMARK).c -o $@

When a user specifies linker flags in USERLDFLAGS (such as --sysroot, -L,
-fuse-ld, or -static) that scripts/cc-can-link.sh validated for
CONFIG_CC_CAN_LINK, building tools/dma via make tools_build will drop those
flags and can fail to link or produce an improperly linked binary.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261102021253.2545235-1-sashal@kernel.org?part=2