Makefile

OUTPUT := .output
CLANG ?= clang
LLVM_STRIP ?= llvm-strip
BPFTOOL_LOCAL ?= ../tools/bpftool
BPFTOOL = $(abspath $(BPFTOOL_LOCAL))
LIBBPF_SRC := $(abspath ../libbpf/src)
LIBBPF_OBJ := $(abspath $(OUTPUT)/libbpf.a)
VMLINUX := $(abspath $(OUTPUT)/vmlinux/vmlinux.h)
# Use our own libbpf API headers and Linux UAPI headers distributed with
# libbpf to avoid dependency on system-wide headers, which could be missing or outdated
INCLUDES := -I$(OUTPUT) -I../libbpf/include/uapi -I$(dir $(VMLINUX))
CFLAGS := -g -Wall
ARCH := $(shell uname -m | sed 's/x86_64/x86/')

APPS = restrict_connect audit_connect kprobe_connect trace_net trace_connect

# Get Clang's default includes on this system. We'll explicitly add these dirs
# to the includes list when compiling with `-target bpf` because otherwise some
# architecture-specific dirs will be "missing" on some architectures/distros -
# headers such as asm/types.h, asm/byteorder.h, asm/socket.h, asm/sockios.h,
# sys/cdefs.h etc. might be missing.
#
# Use '-idirafter': Don't interfere with include mechanics except where the
# build would have failed anyways.
CLANG_BPF_SYS_INCLUDES = $(shell $(CLANG) -v -E - </dev/null 2>&1 \
	| sed -n '/<...> search starts here:/,/End of search list./{ s| \(/.*\)|-idirafter \1|p }')

ifeq ($(V),1)
	Q =
	msg =
else
	Q = @
	msg = @printf '  %-8s %s%s\n'					\
		      "$(1)"						\
		      "$(patsubst $(abspath $(OUTPUT))/%,%,$(2))"	\
		      "$(if $(3), $(3))";
	MAKEFLAGS += --no-print-directory
endif

.PHONY: all
all: $(APPS)

.PHONY: clean
clean:
	$(call msg,CLEAN)
	$(Q)rm -rf $(OUTPUT) $(APPS)
	$(Q)unlink $(BPFTOOL)

$(OUTPUT) $(OUTPUT)/libbpf:
	$(call msg,MKDIR,$@)
	$(Q)mkdir -p $@

# Build libbpf
$(LIBBPF_OBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(OUTPUT)/libbpf
	$(call msg,LIB,$@)
	$(Q)$(MAKE) -C $(LIBBPF_SRC) BUILD_STATIC_ONLY=1		      \
		    OBJDIR=$(dir $@)/libbpf DESTDIR=$(dir $@)		      \
		    INCLUDEDIR= LIBDIR= UAPIDIR=			      \
		    install

# Link bpftool
$(BPFTOOL): $(shell command -v bpftool)
	$(call msg,BPFTOOL,$(BPFTOOL_LOCAL))
	$(Q)$(shell ln -s $< $@)

# Generate vmlinux.h
$(VMLINUX): $(BPFTOOL) /sys/kernel/btf/vmlinux
	$(call msg,MKDIR,$(dir $@))
	$(Q)mkdir -p $(dir $@)
	$(call msg,VMLINUX,$@)
	$(Q)$(BPFTOOL) btf dump file $(word 2,$^) format c > $@

# Build BPF code
$(OUTPUT)/%.bpf.o: %.bpf.c $(LIBBPF_OBJ) $(wildcard %.h) $(VMLINUX) | $(OUTPUT)
	$(call msg,BPF,$@)
	$(Q)$(CLANG) -g -O2 -target bpf -D__TARGET_ARCH_$(ARCH) $(INCLUDES) $(CLANG_BPF_SYS_INCLUDES) -c $(filter %.c,$^) -o $@

# Generate BPF skeletons
$(OUTPUT)/%.skel.h: $(OUTPUT)/%.bpf.o $(BPFTOOL) | $(OUTPUT)
	$(call msg,SKEL,$@)
	$(Q)$(BPFTOOL) gen skeleton $< > $@

# Build user-space code
$(patsubst %,$(OUTPUT)/%.o,$(APPS)): %.o: %.skel.h

$(OUTPUT)/%.o: %.c $(wildcard %.h) | $(OUTPUT)
	$(call msg,CC,$@)
	$(Q)$(CC) $(CFLAGS) $(INCLUDES) -c $(filter %.c,$^) -o $@

# Build application binary
$(APPS): %: $(OUTPUT)/%.o $(LIBBPF_OBJ) | $(OUTPUT)
	$(call msg,BINARY,$@)
	$(Q)$(CC) $(CFLAGS) $^ -lelf -lz -o $@

# delete failed targets
.DELETE_ON_ERROR:

# keep intermediate (.skel.h, .bpf.o, etc) targets
.SECONDARY: