[PATCH v1 11/14] tools build: Integrate libdebuginfod into test-all fast path

[Ian Rogers <irogers@google.com>]

Bundling libdebuginfod into test-all.c allows Make to avoid an individual
feature check sub-make fork during AST parsing. Short-circuit feature_check
in Makefile.feature to instantly skip sub-make evaluations when a feature
was already pre-detected by test-all.

Trade-offs:
On some Linux distributions (e.g., Debian/Ubuntu), libdebuginfod-dev is
packaged separately from libelf-dev and libdw-dev. If a user installs
libdw-dev but omits libdebuginfod-dev, adding -ldebuginfod to BUILD_ALL
causes test-all to fail, falling back to individual feature tests. However,
on fully configured developer workstations, this successfully reclaims
sequential startup latency.

Assisted-by: Gemini:gemini-3.1-pro-preview
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/build/Makefile.feature   | 6 ++++--
 tools/build/feature/Makefile   | 2 +-
 tools/build/feature/test-all.c | 5 +++++
 3 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/tools/build/Makefile.feature b/tools/build/Makefile.feature
index 2f192d3bf61b..d8febe5d5800 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
 
 feature_set = $(eval $(feature_set_code))
@@ -100,6 +102,7 @@ FEATURE_TESTS_BASIC :=                  \
         disassembler-four-args		\
         disassembler-init-styled	\
         file-handle			\
+        libdebuginfod			\
         libopenssl
 
 # FEATURE_TESTS_BASIC + FEATURE_TESTS_EXTRA is the complete list
@@ -125,7 +128,6 @@ FEATURE_TESTS_EXTRA :=                  \
          clang                          \
          libbpf                         \
          libpfm4                        \
-         libdebuginfod			\
          clang-bpf-co-re		\
          bpftool-skeletons
 
diff --git a/tools/build/feature/Makefile b/tools/build/feature/Makefile
index 704c687ed3ad..dc828523b50a 100644
--- a/tools/build/feature/Makefile
+++ b/tools/build/feature/Makefile
@@ -115,7 +115,7 @@ __BUILD = $(CC) $(CFLAGS) -MD -Wall -Werror -o $@ $(patsubst %.bin,%.c,$(@F)) $(
   BUILD_BFD = $(BUILD) -DPACKAGE='"perf"' -lbfd -ldl
   BUILD_ALL = $(BUILD) -fstack-protector-all -O2 -D_FORTIFY_SOURCE=2 -ldw -lelf -lnuma -lelf -lslang \
 	      $(FLAGS_PERL_EMBED) $(FLAGS_PYTHON_EMBED) -ldl -lz -llzma -lzstd \
-	      $(shell $(PKG_CONFIG) --libs --cflags openssl 2>/dev/null)
+	      $(shell $(PKG_CONFIG) --libs --cflags openssl 2>/dev/null) -ldebuginfod
 
 __BUILDXX = $(CXX) $(CXXFLAGS) -MD -Wall -Werror -o $@ $(patsubst %.bin,%.cpp,$(@F)) $(LDFLAGS)
   BUILDXX = $(__BUILDXX) > $(@:.bin=.make.output) 2>&1
diff --git a/tools/build/feature/test-all.c b/tools/build/feature/test-all.c
index 1488bf6e6078..b6984236859f 100644
--- a/tools/build/feature/test-all.c
+++ b/tools/build/feature/test-all.c
@@ -146,6 +146,10 @@
 # include "test-libopenssl.c"
 #undef main
 
+#define main main_test_libdebuginfod
+# include "test-libdebuginfod.c"
+#undef main
+
 int main(int argc, char *argv[])
 {
 	main_test_libpython();
@@ -178,6 +182,7 @@ int main(int argc, char *argv[])
 	main_test_libzstd();
 	main_test_libtraceevent();
 	main_test_libopenssl();
+	main_test_libdebuginfod();
 
 	return 0;
 }
-- 
2.54.0.563.g4f69b47b94-goog