Re: [PATCH v2 02/18] tools build: Integrate libdebuginfod into test-all fast path

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The `ifeq` short-circuit in `feature_check_code` fails to prevent unconditional sub-make evaluations due to eager expansion in `$(eval)`.
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commit e9f96ae598e8b4643d43a93ea3da9bfe004d8b24
Author: Ian Rogers <irogers@google.com>

tools build: Integrate libdebuginfod into test-all fast path

This commit bundles libdebuginfod into the test-all fast path to reclaim
sequential startup latency. It also attempts to short-circuit the
feature_check evaluations to skip sub-make forks when a feature is already
pre-detected.

> diff --git a/tools/build/Makefile.feature b/tools/build/Makefile.feature
> index 2f192d3bf61b9..d8febe5d58005 100644
> --- a/tools/build/Makefile.feature
> +++ b/tools/build/Makefile.feature
> @@ -8,7 +8,9 @@ endif
>  
>  feature_check = $(eval $(feature_check_code))
>  define feature_check_code
> -  feature-$(1) := $(shell $(MAKE) OUTPUT=$(OUTPUT_FEATURES) CC="$(CC)" CXX="$(CXX)" CFLAGS="$(EXTRA_CFLAGS) $(FEATURE_CHECK_CFLAGS-$(1))" CXXFLAGS="$(EXTRA_CXXFLAGS) $(FEATURE_CHECK_CXXFLAGS-$(1))" LDFLAGS="$(LDFLAGS) $(FEATURE_CHECK_LDFLAGS-$(1))" -C $(feature_dir) $(OUTPUT_FEATURES)test-$1.bin >/dev/null 2>/dev/null && echo 1 || echo 0)
> +  ifeq ($(feature-$(1)),)
> +    feature-$(1) := $(shell $(MAKE) OUTPUT=$(OUTPUT_FEATURES) CC="$(CC)" CXX="$(CXX)" CFLAGS="$(EXTRA_CFLAGS) $(FEATURE_CHECK_CFLAGS-$(1))" CXXFLAGS="$(EXTRA_CXXFLAGS) $(FEATURE_CHECK_CXXFLAGS-$(1))" LDFLAGS="$(LDFLAGS) $(FEATURE_CHECK_LDFLAGS-$(1))" -C $(feature_dir) $(OUTPUT_FEATURES)test-$1.bin >/dev/null 2>/dev/null && echo 1 || echo 0)
> +  endif
>  endef

Does this $(shell ...) invocation get evaluated unconditionally before the
ifeq is parsed?

Since feature_check_code is passed to the $(eval ...) function:

feature_check = $(eval $(feature_check_code))

GNU Make expands the arguments to eval completely before parsing them as
Makefile syntax. 

Because the $(shell ...) call is not escaped (for example, as $$(shell ...)),
it appears it will be executed during the initial expansion phase, bypassing
the ifeq condition entirely.

Could this result in the sub-make fork still running unconditionally,
defeating the intended optimization?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260512174638.120445-1-irogers@google.com?part=2