[PATCH v4 4/4] selftests/sched_ext: build BPF schedulers via the shared lib.bpf.mk

[Ziyang Men <ziyang.meme@gmail.com>]

sched_ext carries its own ~130 lines of libbpf + bpftool + vmlinux.h +
BPF-object + skeleton build machinery.  Replace it with an include of the
shared tools/testing/selftests/lib.bpf.mk, making sched_ext the third
in-tree consumer of that fragment, after selftests/cgroup and
selftests/hid.

All generated skeletons and subskeletons keep the same public API, and
the runner is built and linked the same way.

Suggested-by: Eduard Zingerman <eddyz87@gmail.com>
Suggested-by: Mykola Lysenko <mykolal@meta.com>
Assisted-by: Claude:claude-opus-5
Signed-off-by: Ziyang Men <ziyang.meme@gmail.com>
---
 tools/testing/selftests/sched_ext/Makefile | 149 ++++-----------------
 1 file changed, 26 insertions(+), 123 deletions(-)

diff --git a/tools/testing/selftests/sched_ext/Makefile b/tools/testing/selftests/sched_ext/Makefile
index 5d2dffca0e91..856fe7dea685 100644
--- a/tools/testing/selftests/sched_ext/Makefile
+++ b/tools/testing/selftests/sched_ext/Makefile
@@ -14,48 +14,29 @@ CURDIR := $(abspath .)
 REPOROOT := $(abspath ../../../..)
 TOOLSDIR := $(REPOROOT)/tools
 LIBDIR := $(TOOLSDIR)/lib
-BPFDIR := $(LIBDIR)/bpf
 TOOLSINCDIR := $(TOOLSDIR)/include
-BPFTOOLDIR := $(TOOLSDIR)/bpf/bpftool
-APIDIR := $(TOOLSINCDIR)/uapi
 GENDIR := $(REPOROOT)/include/generated
 GENHDR := $(GENDIR)/autoconf.h
-SCXTOOLSDIR := $(TOOLSDIR)/sched_ext
 SCXTOOLSINCDIR := $(TOOLSDIR)/sched_ext/include
 
-OUTPUT_DIR := $(OUTPUT)/build
-OBJ_DIR := $(OUTPUT_DIR)/obj
-INCLUDE_DIR := $(OUTPUT_DIR)/include
-BPFOBJ_DIR := $(OBJ_DIR)/libbpf
-SCXOBJ_DIR := $(OBJ_DIR)/sched_ext
-BPFOBJ := $(BPFOBJ_DIR)/libbpf.a
-LIBBPF_OUTPUT := $(OBJ_DIR)/libbpf/libbpf.a
-
-DEFAULT_BPFTOOL := $(OUTPUT_DIR)/host/sbin/bpftool
-HOST_OBJ_DIR := $(OBJ_DIR)/host/bpftool
-HOST_LIBBPF_OUTPUT := $(OBJ_DIR)/host/libbpf/
-HOST_LIBBPF_DESTDIR := $(OUTPUT_DIR)/host/
-HOST_DESTDIR := $(OUTPUT_DIR)/host/
-
-VMLINUX_BTF_PATHS ?= $(if $(O),$(O)/vmlinux)					\
-		     $(if $(KBUILD_OUTPUT),$(KBUILD_OUTPUT)/vmlinux)		\
-		     ../../../../vmlinux					\
-		     /sys/kernel/btf/vmlinux					\
-		     /boot/vmlinux-$(shell uname -r)
-VMLINUX_BTF ?= $(abspath $(firstword $(wildcard $(VMLINUX_BTF_PATHS))))
-ifeq ($(VMLINUX_BTF),)
-$(error Cannot find a vmlinux for VMLINUX_BTF at any of "$(VMLINUX_BTF_PATHS)")
-endif
+# Build scheduler skeletons and subskeletons with the shared BPF rules.
+BPF_SRCS        := $(wildcard *.bpf.c)
+BPF_SKEL_EXT    := .bpf.skel.h
+BPF_GEN_SUBSKEL := 1
+# Preserve the existing build/ layout.
+BPF_OBJ_DIR  := $(OUTPUT)/build/obj/sched_ext
+BPF_SKEL_DIR := $(OUTPUT)/build/include
+SCXOBJ_DIR   := $(BPF_OBJ_DIR)
 
-BPFTOOL ?= $(DEFAULT_BPFTOOL)
+include ../lib.bpf.mk
 
 ifneq ($(wildcard $(GENHDR)),)
   GENFLAGS := -DHAVE_GENHDR
 endif
 
 CFLAGS += -g -O2 -rdynamic -pthread -Wall -Werror $(GENFLAGS)			\
-	  -I$(INCLUDE_DIR) -I$(GENDIR) -I$(LIBDIR)				\
-	  -I$(TOOLSINCDIR) -I$(APIDIR) -I$(CURDIR)/include -I$(SCXTOOLSINCDIR)
+	  -I$(GENDIR) -I$(LIBDIR) -I$(TOOLSINCDIR) -I$(APIDIR)			\
+	  -I$(CURDIR)/include -I$(SCXTOOLSINCDIR)
 
 # Silence some warnings when compiled with clang
 ifneq ($(LLVM),)
@@ -64,102 +45,26 @@ endif
 
 LDFLAGS = -lelf -lz -lpthread -lzstd
 
-IS_LITTLE_ENDIAN = $(shell $(CC) -dM -E - </dev/null |				\
-			grep 'define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__')
-
-# Get Clang's default includes on this system, as opposed to those seen by
-# '-target bpf'. This fixes "missing" files on some architectures/distros,
-# such as asm/byteorder.h, asm/socket.h, asm/sockios.h, sys/cdefs.h etc.
-#
-# Use '-idirafter': Don't interfere with include mechanics except where the
-# build would have failed anyways.
-define get_sys_includes
-$(shell $(1) $(2) -v -E - </dev/null 2>&1 \
-	| sed -n '/<...> search starts here:/,/End of search list./{ s| \(/.*\)|-idirafter \1|p }') \
-$(shell $(1) $(2) -dM -E - </dev/null | grep '__riscv_xlen ' | awk '{printf("-D__riscv_xlen=%d -D__BITS_PER_LONG=%d", $$3, $$3)}')
-endef
-
-ifneq ($(CROSS_COMPILE),)
-CLANG_TARGET_ARCH = --target=$(notdir $(CROSS_COMPILE:%-=%))
-endif
-
-CLANG_SYS_INCLUDES = $(call get_sys_includes,$(CLANG),$(CLANG_TARGET_ARCH))
-
-BPF_CFLAGS = -g -D__TARGET_ARCH_$(SRCARCH)					\
-	     $(if $(IS_LITTLE_ENDIAN),-mlittle-endian,-mbig-endian)		\
+# Preserve the scheduler-specific flags; the shared recipe adds target flags.
+BPF_CFLAGS = -g -D__TARGET_ARCH_$(SRCARCH) $(MENDIAN)				\
 	     -I$(CURDIR)/include -I$(CURDIR)/include/bpf-compat			\
 	     -I$(INCLUDE_DIR) -I$(APIDIR) -I$(SCXTOOLSINCDIR)			\
 	     -I$(REPOROOT)/include						\
-	     $(CLANG_SYS_INCLUDES) 						\
+	     $(CLANG_SYS_INCLUDES)						\
 	     -Wall -Wno-compare-distinct-pointer-types				\
 	     -Wno-incompatible-function-pointer-types				\
 	     -Wno-microsoft-anon-tag						\
 	     -fms-extensions							\
-	     -O2 -mcpu=v3
-
-# sort removes libbpf duplicates when not cross-building
-MAKE_DIRS := $(sort $(OBJ_DIR)/libbpf $(OBJ_DIR)/libbpf				\
-	       $(OBJ_DIR)/bpftool $(OBJ_DIR)/resolve_btfids			\
-	       $(HOST_OBJ_DIR) $(INCLUDE_DIR) $(SCXOBJ_DIR))
-
-$(MAKE_DIRS):
-	$(call msg,MKDIR,,$@)
-	$(Q)mkdir -p $@
-
-$(BPFOBJ): $(wildcard $(BPFDIR)/*.[ch] $(BPFDIR)/Makefile)			\
-	   $(APIDIR)/linux/bpf.h						\
-	   | $(OBJ_DIR)/libbpf
-	$(Q)$(MAKE) $(submake_extras) -C $(BPFDIR) OUTPUT=$(OBJ_DIR)/libbpf/	\
-		    ARCH=$(ARCH) CC="$(CC)" CROSS_COMPILE=$(CROSS_COMPILE)	\
-		    EXTRA_CFLAGS='-g -O0 -fPIC'					\
-		    DESTDIR=$(OUTPUT_DIR) prefix= all install_headers
-
-$(DEFAULT_BPFTOOL): $(wildcard $(BPFTOOLDIR)/*.[ch] $(BPFTOOLDIR)/Makefile)	\
-		    $(LIBBPF_OUTPUT) | $(HOST_OBJ_DIR)
-	$(Q)$(MAKE) $(submake_extras)  -C $(BPFTOOLDIR)				\
-		    ARCH= CROSS_COMPILE= CC=$(HOSTCC) LD=$(HOSTLD)		\
-		    EXTRA_CFLAGS='-g -O0'					\
-		    OUTPUT=$(HOST_OBJ_DIR)/					\
-		    LIBBPF_OUTPUT=$(HOST_LIBBPF_OUTPUT)				\
-		    LIBBPF_DESTDIR=$(HOST_LIBBPF_DESTDIR)			\
-		    prefix= DESTDIR=$(HOST_DESTDIR) install-bin
-
-$(INCLUDE_DIR)/vmlinux.h: $(VMLINUX_BTF) $(BPFTOOL) | $(INCLUDE_DIR)
-ifeq ($(VMLINUX_H),)
-	$(call msg,GEN,,$@)
-	$(Q)$(BPFTOOL) btf dump file $(VMLINUX_BTF) format c > $@
-else
-	$(call msg,CP,,$@)
-	$(Q)cp "$(VMLINUX_H)" $@
-endif
-
-$(SCXOBJ_DIR)/%.bpf.o: %.bpf.c $(INCLUDE_DIR)/vmlinux.h	| $(BPFOBJ) $(SCXOBJ_DIR)
-	$(call msg,CLNG-BPF,,$(notdir $@))
-	$(Q)$(CLANG) $(BPF_CFLAGS) -target bpf -c $< -o $@
+	     $(BPF_EXTRA_CFLAGS)
 
-$(INCLUDE_DIR)/%.bpf.skel.h: $(SCXOBJ_DIR)/%.bpf.o $(INCLUDE_DIR)/vmlinux.h $(BPFTOOL) | $(INCLUDE_DIR)
-	$(eval sched=$(notdir $@))
-	$(call msg,GEN-SKEL,,$(sched))
-	$(Q)$(BPFTOOL) gen object $(<:.o=.linked1.o) $<
-	$(Q)$(BPFTOOL) gen object $(<:.o=.linked2.o) $(<:.o=.linked1.o)
-	$(Q)$(BPFTOOL) gen object $(<:.o=.linked3.o) $(<:.o=.linked2.o)
-	$(Q)diff $(<:.o=.linked2.o) $(<:.o=.linked3.o)
-	$(Q)$(BPFTOOL) gen skeleton $(<:.o=.linked3.o) name $(subst .bpf.skel.h,,$(sched)) > $@
-	$(Q)$(BPFTOOL) gen subskeleton $(<:.o=.linked3.o) name $(subst .bpf.skel.h,,$(sched)) > $(@:.skel.h=.subskel.h)
+EXTRA_CLEAN += $(OUTPUT)/build
 
 ################
 # C schedulers #
 ################
 
-override define CLEAN
-	rm -rf $(OUTPUT_DIR)
-	rm -f $(TEST_GEN_PROGS)
-endef
-
-# Every testcase takes all of the BPF progs are dependencies by default. This
-# allows testcases to load any BPF scheduler, which is useful for testcases
-# that don't need their own prog to run their test.
-all_test_bpfprogs := $(foreach prog,$(wildcard *.bpf.c),$(INCLUDE_DIR)/$(patsubst %.c,%.skel.h,$(prog)))
+# Build every scheduler before each test.
+all_test_bpfprogs := $(BPF_SKELS)
 
 auto-test-targets :=			\
 	create_dsq			\
@@ -195,24 +100,22 @@ auto-test-targets :=			\
 testcase-targets := $(addsuffix .o,$(addprefix $(SCXOBJ_DIR)/,$(auto-test-targets)))
 
 $(SCXOBJ_DIR)/runner.o: runner.c | $(SCXOBJ_DIR) $(BPFOBJ)
-	$(CC) $(CFLAGS) -c $< -o $@
+	$(call msg,CC,,$@)
+	$(Q)$(CC) $(CFLAGS) -c $< -o $@
 
 # Create all of the test targets object files, whose testcase objects will be
 # registered into the runner in ELF constructors.
-#
-# Note that we must do double expansion here in order to support conditionally
-# compiling BPF object files only if one is present, as the wildcard Make
-# function doesn't support using implicit rules otherwise.
 $(testcase-targets): $(SCXOBJ_DIR)/%.o: %.c $(SCXOBJ_DIR)/runner.o $(all_test_bpfprogs) | $(SCXOBJ_DIR)
-	$(eval test=$(patsubst %.o,%.c,$(notdir $@)))
-	$(CC) $(CFLAGS) -c $< -o $@
+	$(call msg,CC,,$@)
+	$(Q)$(CC) $(CFLAGS) -c $< -o $@
 
 $(SCXOBJ_DIR)/util.o: util.c | $(SCXOBJ_DIR)
-	$(CC) $(CFLAGS) -c $< -o $@
+	$(call msg,CC,,$@)
+	$(Q)$(CC) $(CFLAGS) -c $< -o $@
 
 $(OUTPUT)/runner: $(SCXOBJ_DIR)/runner.o $(SCXOBJ_DIR)/util.o $(BPFOBJ) $(testcase-targets)
-	@echo "$(testcase-targets)"
-	$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
+	$(call msg,BINARY,,$@)
+	$(Q)$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
 
 .DEFAULT_GOAL := all
 
-- 
2.53.0-Meta