The libbpf + bpftool + vmlinux.h + BPF-object + skeleton build tool-chain
is currently duplicated across tools/testing/selftests/{bpf,sched_ext,
hid}/, each carrying ~100-140 lines of near-identical Makefile. As more
subsystems grow BPF-based selftests, the duplication scales poorly.
Add tools/testing/selftests/lib.bpf.mk, a single includable fragment that
provides the whole chain end-to-end. It builds the in-tree libbpf.a and a
host bpftool, generates vmlinux.h from the kernel's BTF, compiles *.bpf.c
into BPF objects (clang --target=bpf) and generates their skeletons. It
also provides what the user-space test binary needs to build: the header
search paths (so #includes resolve), a bpf_link macro that wraps the link
command, and BPF_LDLIBS, so the test can be statically linked against
libbpf.a.
To use: set BPF_SRCS and OVERRIDE_TARGETS := 1 before including ../lib.mk
(so lib.mk's default link rule is suppressed), then include ../lib.bpf.mk
and list $(BPF_SKELS) as prerequisites of the test binary, e.g.,:
BPF_SRCS := progs/foo.bpf.c
OVERRIDE_TARGETS := 1
include ../lib.mk
include ../lib.bpf.mk
$(OUTPUT)/foo_test: foo_test.c $(BPF_SKELS)
$(call bpf_link,$@,$<)
This saves much work for configuring selftests in other folder, such the cgroup.
net/bpf.mk (which only builds *.bpf.o, without skeleton or vmlinux.h
generation) is left unchanged; replacing the existing duplication
mentioned above is the next step.
Suggested-by: Shakeel Butt <[email protected]>
Suggested-by: Eduard Zingerman <[email protected]>
Suggested-by: Mykola Lysenko <[email protected]>
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Ziyang Men <[email protected]>
---
tools/testing/selftests/lib.bpf.mk | 247 +++++++++++++++++++++++++++++
1 file changed, 247 insertions(+)
create mode 100644 tools/testing/selftests/lib.bpf.mk
diff --git a/tools/testing/selftests/lib.bpf.mk
b/tools/testing/selftests/lib.bpf.mk
new file mode 100644
index 000000000000..6f175c6568e9
--- /dev/null
+++ b/tools/testing/selftests/lib.bpf.mk
@@ -0,0 +1,247 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Shared fragment for selftests that compile *.bpf.c into BPF objects +
+# skeletons and link them into userspace test binaries, without each
+# subsystem's Makefile re-implementing the libbpf/bpftool/vmlinux.h machinery.
+#
+# Caller contract (per-test Makefile):
+#
+# BPF_SRCS := foo.bpf.c bar.bpf.c
+# TEST_GEN_PROGS := foo_test
+# OVERRIDE_TARGETS := 1 # MUST be set before lib.mk
+# include ../lib.mk # defines OUTPUT, CC, Q, msg,
+# include ../lib.bpf.mk # selfdir, top_srcdir; honours
OVERRIDE
+#
+# $(OUTPUT)/foo_test: foo_test.c $(BPF_SKELS)
+# $(call bpf_link,$@,$<)
+#
+# Optional knobs (set before including lib.bpf.mk):
+# BPF_PROG_EXT - source suffix, default .bpf.c; set to .c for the legacy
+# "progs/foo.c -> foo.bpf.o" layout.
+# BPF_EXTRA_HDRS - extra prerequisites (headers) for the BPF objects.
+# BPF_EXTRA_CFLAGS - appended to BPF_CFLAGS for the BPF compile.
+# BPF_SKEL_EXT - skeleton suffix, default .skel.h (e.g. .bpf.skel.h).
+# BPF_GEN_SUBSKEL - if set, also emit a subskeleton next to each skeleton.
+# BPF_OBJ_DIR - dir for generated *.bpf.o (default $(OUTPUT)).
+# BPF_SKEL_DIR - dir for generated skeletons (default $(OUTPUT)).
+# A caller with unusual compile needs may override BPF_CFLAGS wholesale after
+# the include (the object recipe expands it lazily).
+# BPF_SRCS entries may live in a subdirectory (e.g. progs/foo.bpf.c); the
+# objects and skeletons are always emitted flat under $(OUTPUT), keyed by the
+# source basename (foo.bpf.o / foo.skel.h).
+#
+# lib.mk MUST be included first: this fragment consumes the vars it defines
+# (OUTPUT, top_srcdir, CC, CLANG, Q, msg) and needs OVERRIDE_TARGETS to have
+# already suppressed lib.mk's default link rule.
+
+include $(top_srcdir)/tools/scripts/Makefile.arch # ARCH / SRCARCH
+# Pull in the shared toolchain definitions (HOSTCC/HOSTLD/CLANG) so this
+# fragment picks the *same* host compiler the libbpf and bpftool sub-makes
+# will: in particular HOSTCC becomes clang under LLVM=1 (gcc otherwise).
+# Without this the host bpftool and its bootstrap libbpf can end up built with
+# a mix of gcc and clang, which trips clang on gcc-only flags
(-Wstrict-aliasing=3).
+#
+# Makefile.include's allow-override resets CC to a bare "clang", which would
+# drop the --target=<arch> flag lib.mk set for LLVM=1 cross builds (make LLVM=1
+# ARCH=arm64). lib.mk ran first and configured CC for the target, so save it
+# across the include and restore it afterwards.
+lib_bpf_mk_saved_cc := $(CC)
+include $(top_srcdir)/tools/scripts/Makefile.include
+CC := $(lib_bpf_mk_saved_cc)
+
+CLANG ?= clang
+HOSTCC ?= gcc
+HOSTLD ?= ld
+ifneq ($(V),1)
+submake_extras := feature_display=0
+endif
+
+# ---- paths & tools --------------------------------------------------------
+TOOLSDIR := $(top_srcdir)/tools
+LIBDIR := $(TOOLSDIR)/lib
+BPFDIR := $(LIBDIR)/bpf
+TOOLSINCDIR := $(TOOLSDIR)/include
+BPFTOOLDIR := $(TOOLSDIR)/bpf/bpftool
+APIDIR := $(TOOLSINCDIR)/uapi
+
+# Everything generated lives under $(OUTPUT) so O= and in-tree both work and
+# per-test builds (distinct $(OUTPUT)) never collide.
+SCRATCH_DIR := $(OUTPUT)/tools
+BUILD_DIR := $(SCRATCH_DIR)/build
+INCLUDE_DIR := $(SCRATCH_DIR)/include
+BPFOBJ := $(BUILD_DIR)/libbpf/libbpf.a
+
+# bpftool must run on the *host*; split the host toolchain out when
cross-building.
+ifneq ($(CROSS_COMPILE),)
+HOST_BUILD_DIR := $(BUILD_DIR)/host
+HOST_SCRATCH_DIR := $(OUTPUT)/host-tools
+else
+HOST_BUILD_DIR := $(BUILD_DIR)
+HOST_SCRATCH_DIR := $(SCRATCH_DIR)
+endif
+HOST_BPFOBJ := $(HOST_BUILD_DIR)/libbpf/libbpf.a
+DEFAULT_BPFTOOL := $(HOST_SCRATCH_DIR)/sbin/bpftool
+BPFTOOL ?= $(DEFAULT_BPFTOOL)
+
+# ---- vmlinux BTF discovery -----------------------------------------------
+VMLINUX_BTF_PATHS ?= $(if $(O),$(O)/vmlinux) \
+ $(if $(KBUILD_OUTPUT),$(KBUILD_OUTPUT)/vmlinux) \
+ $(top_srcdir)/vmlinux \
+ /sys/kernel/btf/vmlinux \
+ /boot/vmlinux-$(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
+
+# ---- clang flags ----------------------------------------------------------
+# Clang's default system includes (not the ones seen under --target=bpf); fixes
+# "missing" asm/byteorder.h etc. '-idirafter' so we never shadow real includes.
+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))
+
+IS_LITTLE_ENDIAN = $(shell $(CC) -dM -E - </dev/null | \
+ grep 'define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__')
+MENDIAN = $(if $(IS_LITTLE_ENDIAN),-mlittle-endian,-mbig-endian)
+
+# Prefer -mcpu=v3; fall back to v2 on clang too old to know it (probed once).
+CLANG_BPF_CPU := $(shell $(CLANG) --target=bpf -mcpu=help 2>&1 | grep -q 'v3' \
+ && echo v3 || echo v2)
+
+# -fms-extensions + -Wno-microsoft-anon-tag: required so clang accepts the
+# anonymous nested struct/union members bpftool emits into vmlinux.h.
+BPF_CFLAGS = -g -Wall -Werror -D__TARGET_ARCH_$(SRCARCH) $(MENDIAN) \
+ -I$(INCLUDE_DIR) -I$(APIDIR) -I$(TOOLSINCDIR) \
+ -std=gnu11 \
+ -fno-strict-aliasing \
+ -fms-extensions -Wno-microsoft-anon-tag \
+ -Wno-compare-distinct-pointer-types \
+ $(CLANG_SYS_INCLUDES) $(BPF_EXTRA_CFLAGS)
+
+# $1 = src .bpf.c, $2 = dst .bpf.o
+define BPF_BUILD_RULE
+ $(call msg,CLNG-BPF,,$2)
+ $(Q)$(CLANG) $(BPF_CFLAGS) -O2 --target=bpf -mcpu=$(CLANG_BPF_CPU) -c
$1 -o $2
+endef
+
+# ---- output dirs for generated objects/skeletons --------------------------
+# Default: flat under $(OUTPUT) (what bpf/, hid/, cgroup/ do). A caller may
+# segregate the generated files into subdirs, e.g. BPF_SKEL_DIR :=
$(OUTPUT)/...
+BPF_OBJ_DIR ?= $(OUTPUT)
+BPF_SKEL_DIR ?= $(OUTPUT)
+
+# ---- scratch dirs ---------------------------------------------------------
+MAKE_DIRS := $(sort $(BUILD_DIR)/libbpf $(HOST_BUILD_DIR)/libbpf
\
+ $(HOST_BUILD_DIR)/bpftool $(INCLUDE_DIR) \
+ $(filter-out $(OUTPUT),$(BPF_OBJ_DIR) $(BPF_SKEL_DIR)))
+$(MAKE_DIRS):
+ $(call msg,MKDIR,,$@)
+ $(Q)mkdir -p $@
+
+# ---- libbpf (target) ------------------------------------------------------
+# Pass ARCH/CROSS_COMPILE/CC through: lib.mk's CC is file-origin and is not
+# exported, so without this the libbpf sub-make would rebuild for the host
under
+# a pure-LLVM cross build (make LLVM=1 ARCH=<arch>). -fPIC keeps the static
+# libbpf linkable into position-independent (PIE) test binaries.
+$(BPFOBJ): $(wildcard $(BPFDIR)/*.[ch] $(BPFDIR)/Makefile) \
+ $(APIDIR)/linux/bpf.h | $(BUILD_DIR)/libbpf
+ $(Q)$(MAKE) $(submake_extras) -C $(BPFDIR) OUTPUT=$(BUILD_DIR)/libbpf/ \
+ ARCH=$(ARCH) CROSS_COMPILE=$(CROSS_COMPILE) CC="$(CC)" \
+ EXTRA_CFLAGS='-g -O0 -fPIC' \
+ DESTDIR=$(SCRATCH_DIR) prefix= all install_headers
+
+# ---- libbpf (host) -- a distinct rule only when cross-compiling -----------
+ifneq ($(BPFOBJ),$(HOST_BPFOBJ))
+$(HOST_BPFOBJ): $(wildcard $(BPFDIR)/*.[ch] $(BPFDIR)/Makefile) \
+ | $(HOST_BUILD_DIR)/libbpf
+ $(Q)$(MAKE) $(submake_extras) -C $(BPFDIR) ARCH= CROSS_COMPILE= \
+ OUTPUT=$(HOST_BUILD_DIR)/libbpf/ CC=$(HOSTCC) LD=$(HOSTLD) \
+ EXTRA_CFLAGS='-g -O0' \
+ DESTDIR=$(HOST_SCRATCH_DIR) prefix= all install_headers
+endif
+
+# ---- bpftool (host) -------------------------------------------------------
+$(DEFAULT_BPFTOOL): $(wildcard $(BPFTOOLDIR)/*.[ch] $(BPFTOOLDIR)/Makefile) \
+ $(HOST_BPFOBJ) | $(HOST_BUILD_DIR)/bpftool
+ $(Q)$(MAKE) $(submake_extras) -C $(BPFTOOLDIR) \
+ ARCH= CROSS_COMPILE= CC=$(HOSTCC) LD=$(HOSTLD) \
+ EXTRA_CFLAGS='-g -O0' \
+ OUTPUT=$(HOST_BUILD_DIR)/bpftool/ \
+ LIBBPF_OUTPUT=$(HOST_BUILD_DIR)/libbpf/ \
+ LIBBPF_DESTDIR=$(HOST_SCRATCH_DIR)/ \
+ prefix= DESTDIR=$(HOST_SCRATCH_DIR)/ install-bin
+
+# ---- vmlinux.h ------------------------------------------------------------
+$(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
+
+# ---- BPF objects + skeletons ---------------------------------------------
+# Sources may sit in a subdir and use the modern *.bpf.c or the legacy *.c
+# suffix (BPF_PROG_EXT); objects go in $(BPF_OBJ_DIR) and skeletons in
+# $(BPF_SKEL_DIR) (both default to $(OUTPUT)), keyed by the source basename.
+BPF_PROG_EXT ?= .bpf.c
+bpf_stems := $(patsubst %$(BPF_PROG_EXT),%,$(notdir $(BPF_SRCS)))
+# The output namespace is flat, so two sources with the same basename would
+# collapse into one object/skeleton; fail loudly instead of silently dropping.
+ifneq ($(words $(bpf_stems)),$(words $(sort $(bpf_stems))))
+$(error lib.bpf.mk: BPF_SRCS has colliding basenames: $(BPF_SRCS))
+endif
+# BPF_SKEL_EXT lets a caller pick the skeleton suffix (default .skel.h; e.g.
+# .bpf.skel.h). With BPF_GEN_SUBSKEL set, a matching subskeleton is emitted
+# alongside (foo.subskel.h / foo.bpf.subskel.h).
+BPF_SKEL_EXT ?= .skel.h
+BPF_SUBSKEL_EXT := $(patsubst %skel.h,%subskel.h,$(BPF_SKEL_EXT))
+BPF_OBJS := $(addprefix $(BPF_OBJ_DIR)/,$(addsuffix .bpf.o,$(bpf_stems)))
+BPF_SKELS := $(addprefix $(BPF_SKEL_DIR)/,$(addsuffix
$(BPF_SKEL_EXT),$(bpf_stems)))
+
+# Locate the sources wherever the caller keeps them (e.g. progs/).
+vpath %$(BPF_PROG_EXT) $(sort $(dir $(BPF_SRCS)))
+
+$(BPF_OBJS): $(BPF_OBJ_DIR)/%.bpf.o: %$(BPF_PROG_EXT) $(BPF_EXTRA_HDRS) \
+ $(wildcard *.bpf.h) $(INCLUDE_DIR)/vmlinux.h | $(BPF_OBJ_DIR)
$(BPFOBJ)
+ $(call BPF_BUILD_RULE,$<,$@)
+
+$(BPF_SKELS): $(BPF_SKEL_DIR)/%$(BPF_SKEL_EXT): $(BPF_OBJ_DIR)/%.bpf.o
$(BPFTOOL) | $(BPF_SKEL_DIR)
+ $(call msg,GEN-SKEL,,$@)
+ $(Q)$(BPFTOOL) gen object $(<:.o=.linked.o) $<
+ $(Q)$(BPFTOOL) gen skeleton $(<:.o=.linked.o) name $(notdir
$(<:.bpf.o=)) > $@
+ifneq ($(BPF_GEN_SUBSKEL),)
+ $(Q)$(BPFTOOL) gen subskeleton $(<:.o=.linked.o) name $(notdir
$(<:.bpf.o=)) > $(@:$(BPF_SKEL_EXT)=$(BPF_SUBSKEL_EXT))
+endif
+
+# ---- exports consumed by the caller --------------------------------------
+# -I$(OUTPUT)/-I$(BPF_SKEL_DIR): so the test .c can #include "foo.skel.h".
+# -I$(INCLUDE_DIR): so userspace can pull in the generated vmlinux.h if needed.
+CFLAGS += -I$(OUTPUT) -I$(BPF_SKEL_DIR) -I$(INCLUDE_DIR)
+
+# Static libbpf.a first, then its deps. libbpf may pull in zstd (BTF
decompress)
+# only when built against it; link -lzstd only if libzstd is present.
+BPF_LDLIBS := $(BPFOBJ) -lelf -lz
+ifneq ($(shell pkg-config --exists libzstd 2>/dev/null && echo y),)
+BPF_LDLIBS += -lzstd
+endif
+
+TEST_GEN_FILES += $(BPF_OBJS)
+
+# Link helper: $1 = output binary, $2 = test .c (skels are the target's deps).
+define bpf_link
+ $(call msg,BINARY,,$1)
+ $(Q)$(CC) $(CFLAGS) $2 $(BPF_LDLIBS) $(LDLIBS) -o $1
+endef
+
+EXTRA_CLEAN += $(SCRATCH_DIR) $(HOST_SCRATCH_DIR) \
+ $(addprefix $(BPF_OBJ_DIR)/,*.bpf.o *.linked.o) \
+ $(addprefix $(BPF_SKEL_DIR)/,*$(BPF_SKEL_EXT)
*$(BPF_SUBSKEL_EXT))
--
2.53.0-Meta
