Makefile

OUTPUT := .output
CLANG ?= clang
LLVM_STRIP ?= llvm-strip
BPFTOOL ?= bpftool
SYS_BTF_VMLINUX := /sys/kernel/btf/vmlinux
VMLINUX := $(OUTPUT)/vmlinux.h

LIBBPF ?= libbpf
LIBBPF_OBJ=$(LIBBPF)/lib64/libbpf.a
XDPTOOLS ?= ../xdp-tutorial/xdp-tools

ARCH := $(shell uname -m | sed 's/x86_64/x86/' | sed 's/aarch64/arm64/' | sed 's/ppc64le/powerpc/' | sed 's/mips.*/mips/')
# Use our own libbpf API headers and Linux UAPI headers distributed with
# libbpf to avoid dependency on system-wide headers, which could be missing or
# outdated
INCLUDES := -I$(OUTPUT) -I$(LIBBPF)/include
CFLAGS := -g -Wall
EXTRA_LDFLAGS := -L$(LIBBPF)/lib64
ALL_LDFLAGS := $(LDFLAGS) $(EXTRA_LDFLAGS) -lbpf -lresolv

APPS = packetstat protostat tccounter skb-drops lpm bloom queue-stack \
	map-o-maps sk-storage dns-trace lru lru-syscall

# 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

define allow-override
  $(if $(or $(findstring environment,$(origin $(1))),\
            $(findstring command line,$(origin $(1)))),,\
    $(eval $(1) = $(2)))
endef

$(call allow-override,CC,$(CROSS_COMPILE)cc)
$(call allow-override,LD,$(CROSS_COMPILE)ld)

.PHONY: all
all: .clangd $(APPS)

.clangd:	.clangd.tmpl
	@sed -e "s?\$${PWD}?${PWD}?g" $< > $@

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

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

# Build BPF code
$(OUTPUT)/%.bpf.o: %.bpf.c $(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 $@
	$(Q)$(LLVM_STRIP) -g $@ # strip useless DWARF info

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

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

$(OUTPUT)/%.o: %.c $(wildcard %.h) $(LIBBPF_OBJ) | $(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) $^ $(ALL_LDFLAGS) -lelf -lz -o $@


# Generate vmlinux.h from kernel BTF
$(VMLINUX):	| $(OUTPUT)
	$(call msg,BTF,$@)
	$(Q)$(BPFTOOL) btf dump file $(SYS_BTF_VMLINUX) format c > $@

# Build and install libbpf from xdp-tutorial/xdp-tools
$(LIBBPF_OBJ):
	$(MAKE) -C $(XDPTOOLS)/lib/libbpf/src install PREFIX=`pwd`/libbpf

# delete failed targets
.DELETE_ON_ERROR:

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