Re: [PATCH v4 4/7] tools: build perf in tools_build

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential
issues to consider:
- [Medium] tools: missing python-config and Python 3.9 check in
  TOOLS_BUILD_PERF_LIBS
- [Medium] tools: TOOLS_BUILD_PERF_LIBS probe mismatches tools/perf
  pkg-config and link checks
--

commit c19562a2a39be79f326367f65fd8b1eb86f840c4
Author: Sasha Levin <sashal@kernel.org>

tools: build perf in tools_build

This commit adds CONFIG_TOOLS_BUILD_PERF and CONFIG_TOOLS_BUILD_PERF_MINIMAL
to build tools/perf as part of tools_build.

> diff --git a/tools/Kconfig b/tools/Kconfig
> index 04896e6b0ca51..ab1e15beb9fe3 100644
> --- a/tools/Kconfig
> +++ b/tools/Kconfig
> @@ -60,6 +60,30 @@ config TOOLS_BUILD_IIO
>  	help
>  	  Build tools/iio (lsiio, iio_event_monitor, iio_generic_buffer).
>  
> +config TOOLS_BUILD_PERF
> +	bool "perf"
> +	help
> +	  Build tools/perf. As in a standalone perf build, optional
> +	  features are enabled when the libraries they need are installed.
> +
> +# What perf does not build without, unless it is built with MINIMAL=1
> +config TOOLS_BUILD_PERF_LIBS
> +	def_bool $(success,command -v $(CROSS_COMPILE)pkg-config || command -v pkg-config) && \
> +		 $(success,echo 'int main(void) { return 0; }' | $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m64-flag) `$(CROSS_COMPILE)pkg-config --cflags --libs libtraceevent 2>/dev/null || pkg-config --cflags --libs libtraceevent` -include libelf.h -include trace-seq.h -x c - -o /dev/null -lelf)

[Severity: Medium]
Can TOOLS_BUILD_PERF_LIBS evaluate to y when tools/perf feature detection for
libtraceevent or libelf will fail?

During a cross-build where $(CROSS_COMPILE)pkg-config is installed on the host
but target libtraceevent.pc is missing, $(CROSS_COMPILE)pkg-config fails and
the || fallback runs the host pkg-config, returning host flags, whereas
tools/perf/Makefile.perf uses $(CROSS_COMPILE)pkg-config exclusively when
present.  Conversely, when $(CROSS_COMPILE)pkg-config is absent,
tools/perf/Makefile.perf exports PKG_CONFIG_LIBDIR for the target multiarch
directories, while the Kconfig check runs host pkg-config with no
PKG_CONFIG_LIBDIR set.

In addition, because pkg-config runs inside backticks without an explicit
-ltraceevent on the compiler command line, a failing pkg-config expands to an
empty string and still succeeds if trace-seq.h is in the include path.
Passing --libs before -x c - and compiling an empty main() without calling
symbols such as elf_begin() or trace_seq_init() also succeeds with static
archives even when transitive dependencies required by tools/build/feature/
checks are missing.

> +
> +config TOOLS_BUILD_PERF_MINIMAL
> +	bool "Build perf with all optional features disabled" if TOOLS_BUILD_PERF_LIBS && !COMPILE_TEST
> +	depends on TOOLS_BUILD_PERF
> +	default !TOOLS_BUILD_PERF_LIBS || COMPILE_TEST

[Severity: Medium]
Does building perf with CONFIG_TOOLS_BUILD_PERF_MINIMAL=n fail when
python3-config is missing or Python is older than 3.9?

Without MINIMAL=1 (which sets NO_JEVENTS=1), x86_64 and arm64 perf builds
enable jevents generation:

tools/perf/Makefile.config:
    ...
    override PYTHON_CONFIG := $(call get-executable-or-default,PYTHON_CONFIG,$(PYTHON_AUTO))
    override PYTHON := $(call get-executable-or-default,PYTHON,$(subst -config,,$(PYTHON_CONFIG)))
    ...
    ifneq ($(NO_JEVENTS),1)
      NO_JEVENTS := 0
      ifndef PYTHON
        $(error ERROR: No python interpreter needed for jevents generation. Install python or build with NO_JEVENTS=1.)
      else
        ifneq ($(PYTHON_39_GOOD), 1)
          $(error ERROR: Python interpreter needed for jevents generation too old (older than 3.9). Install a newer python or build with NO_JEVENTS=1.)
        endif
      endif
    endif

Because Makefile.config derives PYTHON from PYTHON_CONFIG (python3-config or
python-config, typically packaged in python3-dev / python3-devel rather than
the base python3 package) and TOOLS_BUILD_PERF_LIBS does not check for it or
Python >= 3.9, TOOLS_BUILD_PERF_MINIMAL defaults to n and the perf build
aborts when pkg-config, libelf, and libtraceevent are installed without
python3-config.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261112195427.3411746-1-sashal@kernel.org?part=4