Re: [PATCH 2/3] perf build: Apply EXTRA_CXXFLAGS to C++ builds

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [Medium] C++ feature detection tests do not receive `EXTRA_CFLAGS`, causing a structural mismatch between feature detection and actual build compilation flags.
- [Low] Injecting `EXTRA_CFLAGS` into `CXXFLAGS` breaks C++ builds when C-specific flags are present.
--

--- Patch [2]: [PATCH 2/3] perf build: Apply EXTRA_CXXFLAGS to C++ builds ---
commit 4b2b9e4dd8644e0e1fa95ec876a875596e1e9178
Author: Trevor Allison <tallison@redhat.com>

perf build: Apply EXTRA_CXXFLAGS to C++ builds

The commit initializes CXXFLAGS in tools/perf/Makefile.config with both
EXTRA_CXXFLAGS and EXTRA_CFLAGS so that C++ objects receive the same builder
flags as the rest of perf.

> diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
> index 0ba307e78fe1f..052a6cc7942f9 100644
> --- a/tools/perf/Makefile.config
> +++ b/tools/perf/Makefile.config
> @@ -17,6 +17,7 @@ detected     = $(shell echo "$(1)=y"       >> $(OUTPUT).config-detected)
>  detected_var = $(shell echo "$(1)=$($(1))" >> $(OUTPUT).config-detected)
>  
>  CFLAGS := $(EXTRA_CFLAGS) $(filter-out -Wnested-externs,$(EXTRA_WARNINGS))
> +CXXFLAGS := $(EXTRA_CXXFLAGS) $(EXTRA_CFLAGS)

[Severity: Low]
Could this cause a build regression if EXTRA_CFLAGS contains C-only flags?

If EXTRA_CFLAGS contains flags that are only valid for C/ObjC (such as
-Wstrict-prototypes), applying them to C++ files causes compiler warnings.
With -Werror enabled, this results in a build failure.

[Severity: Medium]
Does this create a mismatch between feature detection and the main build?

While CXXFLAGS here receives EXTRA_CFLAGS, the C++ feature detection tests in
tools/build/Makefile.feature still only use:

CXXFLAGS="$(EXTRA_CXXFLAGS) $(FEATURE_CHECK_CXXFLAGS-$(1))"

If EXTRA_CFLAGS contains mandatory compiler flags like --sysroot or -m32,
the C++ feature detection tests will fail without EXTRA_CFLAGS. This causes
false negatives where the perf binary silently lacks supported features,
despite the main build succeeding.

>  HOSTCFLAGS := $(filter-out -Wnested-externs,$(EXTRA_WARNINGS))

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260708045606.43649-1-tallison@redhat.com?part=2