perf build: Install libbpf headers locally when building

API headers from libbpf should not be accessed directly from the
library's source directory. Instead, they should be exported with "make
install_headers". Let's adjust perf's Makefile to install those headers
locally when building libbpf.

v2:

- Fix $(LIBBPF_OUTPUT) when $(OUTPUT) is null.
- Make sure the recipe for $(LIBBPF_OUTPUT) is not under a "ifdef".
Signed-off-by: Quentin Monnet <quentin@isovalent.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: bpf@vger.kernel.org
Cc: netdev@vger.kernel.org
Link: http://lore.kernel.org/lkml/20211107002445.4790-1-quentin@isovalent.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Makefile.perf

@@ -243,7 +243,7 @@ else # force_fixdep
 
 LIB_DIR         = $(srctree)/tools/lib/api/
 TRACE_EVENT_DIR = $(srctree)/tools/lib/traceevent/
-BPF_DIR         = $(srctree)/tools/lib/bpf/
+LIBBPF_DIR      = $(srctree)/tools/lib/bpf/
 SUBCMD_DIR      = $(srctree)/tools/lib/subcmd/
 LIBPERF_DIR     = $(srctree)/tools/lib/perf/
 DOC_DIR         = $(srctree)/tools/perf/Documentation/
@@ -295,7 +295,6 @@ strip-libs = $(filter-out -l%,$(1))
 ifneq ($(OUTPUT),)
   TE_PATH=$(OUTPUT)
   PLUGINS_PATH=$(OUTPUT)
-  BPF_PATH=$(OUTPUT)
   SUBCMD_PATH=$(OUTPUT)
   LIBPERF_PATH=$(OUTPUT)
 ifneq ($(subdir),)
@@ -307,7 +306,6 @@ else
   TE_PATH=$(TRACE_EVENT_DIR)
   PLUGINS_PATH=$(TRACE_EVENT_DIR)plugins/
   API_PATH=$(LIB_DIR)
-  BPF_PATH=$(BPF_DIR)
   SUBCMD_PATH=$(SUBCMD_DIR)
   LIBPERF_PATH=$(LIBPERF_DIR)
 endif
@@ -326,7 +324,14 @@ LIBTRACEEVENT_DYNAMIC_LIST_LDFLAGS = $(if $(findstring -static,$(LDFLAGS)),,$(DY
 LIBAPI = $(API_PATH)libapi.a
 export LIBAPI
 
-LIBBPF = $(BPF_PATH)libbpf.a
+ifneq ($(OUTPUT),)
+  LIBBPF_OUTPUT = $(abspath $(OUTPUT))/libbpf
+else
+  LIBBPF_OUTPUT = $(CURDIR)/libbpf
+endif
+LIBBPF_DESTDIR = $(LIBBPF_OUTPUT)
+LIBBPF_INCLUDE = $(LIBBPF_DESTDIR)/include
+LIBBPF = $(LIBBPF_OUTPUT)/libbpf.a
 
 LIBSUBCMD = $(SUBCMD_PATH)libsubcmd.a
 
@@ -831,12 +836,14 @@ $(LIBAPI)-clean:
 	$(call QUIET_CLEAN, libapi)
 	$(Q)$(MAKE) -C $(LIB_DIR) O=$(OUTPUT) clean >/dev/null
 
-$(LIBBPF): FORCE
-	$(Q)$(MAKE) -C $(BPF_DIR) O=$(OUTPUT) $(OUTPUT)libbpf.a FEATURES_DUMP=$(FEATURE_DUMP_EXPORT)
+$(LIBBPF): FORCE | $(LIBBPF_OUTPUT)
+	$(Q)$(MAKE) -C $(LIBBPF_DIR) FEATURES_DUMP=$(FEATURE_DUMP_EXPORT) \
+		O= OUTPUT=$(LIBBPF_OUTPUT)/ DESTDIR=$(LIBBPF_DESTDIR) prefix= \
+		$@ install_headers
 
 $(LIBBPF)-clean:
 	$(call QUIET_CLEAN, libbpf)
-	$(Q)$(MAKE) -C $(BPF_DIR) O=$(OUTPUT) clean >/dev/null
+	$(Q)$(RM) -r -- $(LIBBPF_OUTPUT)
 
 $(LIBPERF): FORCE
 	$(Q)$(MAKE) -C $(LIBPERF_DIR) EXTRA_CFLAGS="$(LIBPERF_CFLAGS)" O=$(OUTPUT) $(OUTPUT)libperf.a
@@ -1036,16 +1043,15 @@ SKELETONS := $(SKEL_OUT)/bpf_prog_profiler.skel.h
 SKELETONS += $(SKEL_OUT)/bperf_leader.skel.h $(SKEL_OUT)/bperf_follower.skel.h
 SKELETONS += $(SKEL_OUT)/bperf_cgroup.skel.h
 
+$(SKEL_TMP_OUT) $(LIBBPF_OUTPUT):
+	$(Q)$(MKDIR) -p $@
+
 ifdef BUILD_BPF_SKEL
 BPFTOOL := $(SKEL_TMP_OUT)/bootstrap/bpftool
-LIBBPF_SRC := $(abspath ../lib/bpf)
-BPF_INCLUDE := -I$(SKEL_TMP_OUT)/.. -I$(BPF_PATH) -I$(LIBBPF_SRC)/..
-
-$(SKEL_TMP_OUT):
-	$(Q)$(MKDIR) -p $@
+BPF_INCLUDE := -I$(SKEL_TMP_OUT)/.. -I$(LIBBPF_INCLUDE)
 
 $(BPFTOOL): | $(SKEL_TMP_OUT)
-	CFLAGS= $(MAKE) -C ../bpf/bpftool \
+	$(Q)CFLAGS= $(MAKE) -C ../bpf/bpftool \
 		OUTPUT=$(SKEL_TMP_OUT)/ bootstrap
 
 VMLINUX_BTF_PATHS ?= $(if $(O),$(O)/vmlinux)				\