Setup development environment with libbpf

src/Makefile

@@ -0,0 +1,93 @@
+# SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
+OUTPUT := .output
+CLANG ?= clang
+LLVM_STRIP ?= llvm-strip
+BPFTOOL ?= $(abspath ./tools/bpftool)
+LIBBPF_SRC := $(abspath ./libbpf/src)
+LIBBPF_OBJ := $(abspath $(OUTPUT)/libbpf.a)
+VMLINUX := ./vmlinux/vmlinux.h
+USER := user
+EBPF := ebpf
+# Use our own libbpf API headers and Linux UAPI headers distributed with
+# libbpf to avoid dependency on system-wide headers, which could be missing or
+# outdated
+INCLUDES := -I$(OUTPUT) -I./libbpf/include/uapi -I$(dir $(VMLINUX))
+CFLAGS := -g -Wall
+ARCH := $(shell uname -m | sed 's/x86_64/x86/')
+
+APPS = minimal bootstrap
+
+# 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 $(OUTPUT) user/$(APPS)
+	$(Q)rm -rf $(OUTPUT) ebpf/$(APPS)
+	$(Q)rm -rf $(OUTPUT) bin/*
+
+$(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 $@)		      \
+		    INCLUDEDIR= LIBDIR= UAPIDIR=			      \
+		    install
+
+# Build BPF code
+$(OUTPUT)/%.bpf.o: $(EBPF)/%.bpf.c $(LIBBPF_OBJ) $(wildcard $(EBPF)/%.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: $(USER)/%.c $(wildcard $(USER)/%.h) | $(OUTPUT)
+	$(call msg,CC,$@)
+	$(Q)$(CC) $(CFLAGS) $(INCLUDES) -c $(filter $(USER)/%.c,$^) -o $@
+
+# Build application binary
+$(APPS): %: $(OUTPUT)/%.o $(LIBBPF_OBJ) | $(OUTPUT)
+	$(call msg,BINARY,$@)
+	$(Q)$(CC) $(CFLAGS) $^ -lelf -lz -o bin/$@
+
+# delete failed targets
+.DELETE_ON_ERROR:
+
+# keep intermediate (.skel.h, .bpf.o, etc) targets
+.SECONDARY:
+