# SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
OUTPUT := .output
LIBDIR ?= /usr/lib64
SBINDIR ?= /usr/sbin
UNITDIR ?= /usr/lib/systemd/system
CLANG ?= clang
VMLINUX_BTF ?= /sys/kernel/btf/vmlinux
LIBBPF_SRC := $(abspath ./libbpf/src)
ifdef FORCE_SYSTEM_LIBBPF
	LIBBPF_OBJ := $(LIBDIR)/libbpf.so
else
	LIBBPF_OBJ := $(abspath $(OUTPUT)/libbpf.a)
endif
BPFTOOL ?= /usr/sbin/bpftool
ARCH ?= $(shell uname -m | sed 's/x86_64/x86/' \
			 | sed 's/arm.*/arm/' \
			 | sed 's/aarch64/arm64/' \
			 | sed 's/ppc64le/powerpc/' \
			 | sed 's/mips.*/mips/' \
			 | sed 's/riscv64/riscv/' \
			 | sed 's/loongarch64/loongarch/')
# Use our own libbpf API headers and Linux UAPI headers distributed with
# libbpf to avoid dependency on system-wide headers, which could be missing or
# outdated
INCLUDES := -I$(OUTPUT)
CFLAGS := -g -Wall
ALL_LDFLAGS := $(LDFLAGS) $(EXTRA_LDFLAGS)
BPF_CFLAGS :=

APPS = sysctl-logger

# 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: $(APPS)

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

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

ifndef FORCE_SYSTEM_LIBBPF
# 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
endif

ifdef CGROUP_CURRENT_FUNC_PROTO
BPF_CFLAGS += -DHAVE_CGROUP_CURRENT_FUNC_PROTO
endif

$(OUTPUT)/vmlinux.h: | $(OUTPUT) $(BPFTOOL)
	$(Q)$(BPFTOOL) btf dump file $(VMLINUX_BTF) format c >$@

# Build BPF code
$(OUTPUT)/%.bpf.o: %.bpf.c $(LIBBPF_OBJ) $(wildcard %.h) $(OUTPUT)/vmlinux.h | $(OUTPUT) $(BPFTOOL)
	$(call msg,BPF,$@)
	$(Q)$(CLANG) -g -O2 -target bpf -D__TARGET_ARCH_$(ARCH)		      \
		     $(INCLUDES) $(CLANG_BPF_SYS_INCLUDES) $(BPF_CFLAGS)      \
		     -c $(filter %.c,$^) -o $(patsubst %.bpf.o,%.tmp.bpf.o,$@)
	$(Q)$(BPFTOOL) gen object $@ $(patsubst %.bpf.o,%.tmp.bpf.o,$@)

# Generate BPF skeletons
$(OUTPUT)/%.skel.h: $(OUTPUT)/%.bpf.o | $(OUTPUT) $(BPFTOOL)
	$(call msg,GEN-SKEL,$@)
	$(Q)$(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) $^ $(ALL_LDFLAGS) -lelf -lz -o $@

$(OUTPUT)/sysctl-logger.service: sysctl-logger.service.in | $(OUTPUT)
	SBINDIR=$(SBINDIR) envsubst < $^ > $@

install: $(APPS) $(OUTPUT)/sysctl-logger.service
	install -d $(DESTDIR)$(SBINDIR)
	install -m 755 sysctl-logger $(DESTDIR)$(SBINDIR)/sysctl-logger
	install -d $(DESTDIR)$(UNITDIR)
	install -m 644 $(OUTPUT)/sysctl-logger.service $(DESTDIR)$(UNITDIR)/sysctl-logger.service

# delete failed targets
.DELETE_ON_ERROR:

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