[PATCH v2 09/18] perf build: Encapsulate vmlinux.h and bpftool in bpf_skel.mak

[Ian Rogers <irogers@google.com>]

Currently, bpftool and vmlinux.h are prerequisites of the top-level
prepare target in Makefile.perf. This unnecessarily blocks the massive
parallel C compilation of libraries (perf-util, perf-ui, pmu-events) during
the initial startup phase.

Move all bpftool and vmlinux.h generation rules down into
tools/perf/bpf_skel.mak to encapsulate BPF tooling completely within the
skeleton framework. Remove them entirely from prepare to unblock immediate
parallel build execution.

To prevent parallel sub-makes (perf-util and perf-bench) from racing to
build shared prerequisites concurrently, while maintaining strict directory
encapsulation without top-level inclusions, serialize bench after the util
static archive finishes using an order-only prerequisite:
  $(LIBPERF_BENCH_IN): FORCE prepare | $(LIBPERF_UTIL)

Tested-by: James Clark <james.clark@linaro.org>
Assisted-by: Gemini:gemini-3.1-pro-preview
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/Makefile.config |  2 +-
 tools/perf/Makefile.perf   | 61 +++++---------------------------------
 tools/perf/bpf_skel.mak    | 47 +++++++++++++++++++++++++++++
 3 files changed, 55 insertions(+), 55 deletions(-)

diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
index 06d7a3f9990c..bc1111c88226 100644
--- a/tools/perf/Makefile.config
+++ b/tools/perf/Makefile.config
@@ -736,7 +736,7 @@ ifeq ($(BUILD_BPF_SKEL),1)
 endif
 
 ifndef GEN_VMLINUX_H
-  VMLINUX_H=$(src-perf)/util/bpf_skel/vmlinux/vmlinux.h
+  VMLINUX_H_FILE=$(src-perf)/util/bpf_skel/vmlinux/vmlinux.h
 endif
 
 dwarf-post-unwind := 1
diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
index d4fc10f36781..ec0e91bedce1 100644
--- a/tools/perf/Makefile.perf
+++ b/tools/perf/Makefile.perf
@@ -274,7 +274,7 @@ ifeq ($(PYLINT),1)
   PYLINT := $(shell which pylint 2> /dev/null)
 endif
 
-export srctree OUTPUT RM CC CXX RUSTC CLANG LD AR CFLAGS CXXFLAGS RUST_FLAGS V BISON FLEX AWK LIBBPF
+export srctree OUTPUT RM CC CXX RUSTC CLANG LD AR CFLAGS CXXFLAGS RUST_FLAGS V BISON FLEX AWK LIBBPF READELF
 export HOSTCC HOSTLD HOSTAR HOSTCFLAGS SHELLCHECK MYPY PYLINT
 
 include $(srctree)/tools/build/Makefile.include
@@ -324,7 +324,7 @@ else
 FEATURE_DUMP_EXPORT := $(realpath $(FEATURES_DUMP))
 endif
 
-export prefix bindir sharedir sysconfdir DESTDIR
+export prefix bindir sharedir sysconfdir DESTDIR VMLINUX_H_FILE
 
 # sparse is architecture-neutral, which means that we need to tell it
 # explicitly what architecture to check for. Fix this up for yours..
@@ -556,7 +556,9 @@ $(LIBPMU_EVENTS_IN): FORCE $(LIBPERF)
 $(LIBPMU_EVENTS): $(LIBPMU_EVENTS_IN)
 	$(QUIET_AR)$(RM) $@ && $(AR) rcs $@ $<
 
-$(LIBPERF_BENCH_IN): FORCE prepare
+# The $(LIBPERF_UTIL) dependency is to ensure bpftool and vmlinux.h
+# aren't racily built for bench/bpf_skel/bench_uprobe.bpf.c
+$(LIBPERF_BENCH_IN): FORCE prepare | $(LIBPERF_UTIL)
 	$(Q)$(MAKE) $(build)=perf-bench
 
 $(LIBPERF_BENCH): $(LIBPERF_BENCH_IN)
@@ -911,60 +913,11 @@ $(INSTALL_DOC_TARGETS):
 python-clean:
 	$(python-clean)
 
-SKEL_OUT := $(abspath $(OUTPUT)util/bpf_skel)
-SKEL_TMP_OUT := $(abspath $(SKEL_OUT)/.tmp)
-
-$(SKEL_TMP_OUT) $(LIBAPI_OUTPUT) $(LIBBPF_OUTPUT) $(LIBPERF_OUTPUT) $(LIBSUBCMD_OUTPUT) $(LIBSYMBOL_OUTPUT):
+$(LIBAPI_OUTPUT) $(LIBBPF_OUTPUT) $(LIBPERF_OUTPUT) $(LIBSUBCMD_OUTPUT) $(LIBSYMBOL_OUTPUT):
 	$(Q)$(MKDIR) -p $@
 
-ifeq ($(CONFIG_PERF_BPF_SKEL),y)
-prepare: $(BPFTOOL) $(SKEL_OUT)/vmlinux.h
-BPFTOOL := $(SKEL_TMP_OUT)/bootstrap/bpftool
-
-$(BPFTOOL): | $(SKEL_TMP_OUT)
-	$(Q)CFLAGS= $(MAKE) -C ../bpf/bpftool \
-		OUTPUT=$(SKEL_TMP_OUT)/ bootstrap
-
-# Paths to search for a kernel to generate vmlinux.h from.
-VMLINUX_BTF_ELF_PATHS ?= $(if $(O),$(O)/vmlinux)			\
-		     $(if $(KBUILD_OUTPUT),$(KBUILD_OUTPUT)/vmlinux)	\
-		     ../../vmlinux					\
-		     /boot/vmlinux-$(shell uname -r)
-
-# Paths to BTF information.
-VMLINUX_BTF_BTF_PATHS ?= /sys/kernel/btf/vmlinux
-
-# Filter out kernels that don't exist or without a BTF section.
-VMLINUX_BTF_ELF_ABSPATHS ?= $(abspath $(wildcard $(VMLINUX_BTF_ELF_PATHS)))
-VMLINUX_BTF_PATHS ?= $(shell for file in $(VMLINUX_BTF_ELF_ABSPATHS); \
-			do \
-				if [ -f $$file ] && ($(READELF) -S "$$file" | grep -q .BTF); \
-				then \
-					echo "$$file"; \
-				fi; \
-			done) \
-			$(wildcard $(VMLINUX_BTF_BTF_PATHS))
-
-# Select the first as the source of vmlinux.h.
-VMLINUX_BTF ?= $(firstword $(VMLINUX_BTF_PATHS))
-
-ifeq ($(VMLINUX_H),)
-  ifeq ($(VMLINUX_BTF),)
-    $(error Missing bpftool input for generating vmlinux.h)
-  endif
-endif
-
-$(SKEL_OUT)/vmlinux.h: $(VMLINUX_BTF) $(BPFTOOL) $(VMLINUX_H)
-ifeq ($(VMLINUX_H),)
-	$(QUIET_GEN)$(BPFTOOL) btf dump file $< format c > $@
-else
-	$(Q)cp "$(VMLINUX_H)" $@
-endif
-
-endif # CONFIG_PERF_BPF_SKEL
-
 bpf-skel-clean:
-	$(call QUIET_CLEAN, bpf-skel) $(RM) -r $(SKEL_TMP_OUT) $(SKEL_OUT)/*.skel.h $(SKEL_OUT)/vmlinux.h $(OUTPUT)bench/bpf_skel/*.skel.h
+	$(Q)$(MAKE) -f bpf_skel.mak clean
 
 pmu-events-clean:
 ifeq ($(OUTPUT),)
diff --git a/tools/perf/bpf_skel.mak b/tools/perf/bpf_skel.mak
index bcb704d5af32..ded578b9570c 100644
--- a/tools/perf/bpf_skel.mak
+++ b/tools/perf/bpf_skel.mak
@@ -36,6 +36,47 @@ ifneq ($(WERROR),0)
   CLANG_OPTIONS += -Werror
 endif
 
+$(BPFTOOL):
+	$(Q)mkdir -p $(SKEL_TOOL_TMP_OUT)
+	$(Q)CFLAGS= $(MAKE) -C ../bpf/bpftool OUTPUT=$(SKEL_TOOL_TMP_OUT)/ bootstrap
+
+# Paths to search for a kernel to generate vmlinux.h from.
+VMLINUX_BTF_ELF_PATHS ?= $(if $(O),$(O)/vmlinux)			\
+		     $(if $(KBUILD_OUTPUT),$(KBUILD_OUTPUT)/vmlinux)	\
+		     ../../vmlinux					\
+		     /boot/vmlinux-$(shell uname -r)
+
+# Paths to BTF information.
+VMLINUX_BTF_BTF_PATHS ?= /sys/kernel/btf/vmlinux
+
+# Filter out kernels that don't exist or without a BTF section.
+VMLINUX_BTF_ELF_ABSPATHS ?= $(abspath $(wildcard $(VMLINUX_BTF_ELF_PATHS)))
+VMLINUX_BTF_PATHS ?= $(shell for file in $(VMLINUX_BTF_ELF_ABSPATHS); \
+			do \
+				if [ -f $$file ] && ($(READELF) -S "$$file" | grep -q .BTF); \
+				then \
+					echo "$$file"; \
+				fi; \
+			done) \
+			$(wildcard $(VMLINUX_BTF_BTF_PATHS))
+
+# Select the first as the source of vmlinux.h.
+VMLINUX_BTF ?= $(firstword $(VMLINUX_BTF_PATHS))
+
+ifeq ($(VMLINUX_H_FILE),)
+  ifeq ($(VMLINUX_BTF),)
+    $(error Missing bpftool input for generating vmlinux.h)
+  endif
+endif
+
+$(VMLINUX_H): $(VMLINUX_BTF) $(BPFTOOL) $(VMLINUX_H_FILE)
+	$(call rule_mkdir)
+ifeq ($(VMLINUX_H_FILE),)
+	$(QUIET_GEN)$(BPFTOOL) btf dump file $< format c > $@
+else
+	$(Q)cp "$(VMLINUX_H_FILE)" $@
+endif
+
 # Consolidated Pattern rule for $(dir)/bpf_skel/
 $(SKEL_TMP_OUT)/%.bpf.o: $(srctree)/tools/perf/$(dir)/bpf_skel/%.bpf.c $(LIBBPF) $(VMLINUX_H) $(OUTPUT)PERF-VERSION-FILE util/bpf_skel/perf_version.h
 	$(call rule_mkdir)
@@ -52,4 +93,10 @@ $(SKEL_OUT)/%.skel.h: $(SKEL_TMP_OUT)/%.bpf.o $(BPFTOOL)
 	$(Q)$(BPFTOOL) gen skeleton $< > $@
 
 .PRECIOUS: $(SKEL_TMP_OUT)/%.bpf.o
+
 endif # CONFIG_PERF_BPF_SKEL
+
+clean:
+	$(call QUIET_CLEAN, bpf-skel) $(RM) -r $(SKEL_TOOL_TMP_OUT) $(OUTPUT)bench/bpf_skel/.tmp $(SKEL_TOOL_OUT)/*.skel.h $(OUTPUT)bench/bpf_skel/*.skel.h $(SKEL_TOOL_OUT)/vmlinux.h
+
+.PHONY: clean
-- 
2.54.0.563.g4f69b47b94-goog