tools/resolve_btfids: Install libbpf headers 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 make sure that resolve_btfids installs the
headers properly when building.

When descending from a parent Makefile, the specific output directories
for building the library and exporting the headers are configurable with
LIBBPF_OUT and LIBBPF_DESTDIR, respectively. This is in addition to
OUTPUT, on top of which those variables are constructed by default.

Also adjust the Makefile for the BPF selftests in order to point to the
(target) libbpf shared with other tools, instead of building a version
specific to resolve_btfids. Remove libbpf's order-only dependencies on
the include directories (they are created by libbpf and don't need to
exist beforehand).

Signed-off-by: Quentin Monnet <quentin@isovalent.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211007194438.34443-5-quentin@isovalent.com

tools/bpf/resolve_btfids/Makefile

@@ -29,25 +29,30 @@ BPFOBJ     := $(OUTPUT)/libbpf/libbpf.a
 LIBBPF_OUT := $(abspath $(dir $(BPFOBJ)))/
 SUBCMDOBJ  := $(OUTPUT)/libsubcmd/libsubcmd.a
 
+LIBBPF_DESTDIR := $(LIBBPF_OUT)
+LIBBPF_INCLUDE := $(LIBBPF_DESTDIR)include
+
 BINARY     := $(OUTPUT)/resolve_btfids
 BINARY_IN  := $(BINARY)-in.o
 
 all: $(BINARY)
 
-$(OUTPUT) $(OUTPUT)/libbpf $(OUTPUT)/libsubcmd:
+$(OUTPUT) $(OUTPUT)/libsubcmd $(LIBBPF_OUT):
 	$(call msg,MKDIR,,$@)
 	$(Q)mkdir -p $(@)
 
 $(SUBCMDOBJ): fixdep FORCE | $(OUTPUT)/libsubcmd
 	$(Q)$(MAKE) -C $(SUBCMD_SRC) OUTPUT=$(abspath $(dir $@))/ $(abspath $@)
 
-$(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(OUTPUT)/libbpf
-	$(Q)$(MAKE) $(submake_extras) -C $(LIBBPF_SRC)  OUTPUT=$(LIBBPF_OUT) $(abspath $@)
+$(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OUT)
+	$(Q)$(MAKE) $(submake_extras) -C $(LIBBPF_SRC) OUTPUT=$(LIBBPF_OUT)    \
+		    DESTDIR=$(LIBBPF_DESTDIR) prefix=			       \
+		    $(abspath $@) install_headers
 
 CFLAGS := -g \
           -I$(srctree)/tools/include \
           -I$(srctree)/tools/include/uapi \
-          -I$(LIBBPF_SRC) \
+          -I$(LIBBPF_INCLUDE) \
           -I$(SUBCMD_SRC)
 
 LIBS = -lelf -lz
@@ -65,7 +70,8 @@ $(BINARY): $(BPFOBJ) $(SUBCMDOBJ) $(BINARY_IN)
 clean_objects := $(wildcard $(OUTPUT)/*.o                \
                             $(OUTPUT)/.*.o.cmd           \
                             $(OUTPUT)/.*.o.d             \
-                            $(OUTPUT)/libbpf             \
+                            $(LIBBPF_OUT)                \
+                            $(LIBBPF_DESTDIR)            \
                             $(OUTPUT)/libsubcmd          \
                             $(OUTPUT)/resolve_btfids)
 

tools/bpf/resolve_btfids/main.c

@@ -60,8 +60,8 @@
 #include <linux/rbtree.h>
 #include <linux/zalloc.h>
 #include <linux/err.h>
-#include <btf.h>
-#include <libbpf.h>
+#include <bpf/btf.h>
+#include <bpf/libbpf.h>
 #include <parse-options.h>
 
 #define BTF_IDS_SECTION	".BTF_ids"

tools/testing/selftests/bpf/Makefile

@@ -122,9 +122,11 @@ BPFOBJ := $(BUILD_DIR)/libbpf/libbpf.a
 ifneq ($(CROSS_COMPILE),)
 HOST_BUILD_DIR		:= $(BUILD_DIR)/host
 HOST_SCRATCH_DIR	:= $(OUTPUT)/host-tools
+HOST_INCLUDE_DIR	:= $(HOST_SCRATCH_DIR)/include
 else
 HOST_BUILD_DIR		:= $(BUILD_DIR)
 HOST_SCRATCH_DIR	:= $(SCRATCH_DIR)
+HOST_INCLUDE_DIR	:= $(INCLUDE_DIR)
 endif
 HOST_BPFOBJ := $(HOST_BUILD_DIR)/libbpf/libbpf.a
 RESOLVE_BTFIDS := $(HOST_BUILD_DIR)/resolve_btfids/resolve_btfids
@@ -227,7 +229,7 @@ docs-clean:
 
 $(BPFOBJ): $(wildcard $(BPFDIR)/*.[ch] $(BPFDIR)/Makefile)		       \
 	   ../../../include/uapi/linux/bpf.h                                   \
-	   | $(INCLUDE_DIR) $(BUILD_DIR)/libbpf
+	   | $(BUILD_DIR)/libbpf
 	$(Q)$(MAKE) $(submake_extras) -C $(BPFDIR) OUTPUT=$(BUILD_DIR)/libbpf/ \
 		    EXTRA_CFLAGS='-g -O0'				       \
 		    DESTDIR=$(SCRATCH_DIR) prefix= all install_headers
@@ -235,7 +237,7 @@ $(BPFOBJ): $(wildcard $(BPFDIR)/*.[ch] $(BPFDIR)/Makefile)		       \
 ifneq ($(BPFOBJ),$(HOST_BPFOBJ))
 $(HOST_BPFOBJ): $(wildcard $(BPFDIR)/*.[ch] $(BPFDIR)/Makefile)                \
 	   ../../../include/uapi/linux/bpf.h                                   \
-	   | $(INCLUDE_DIR) $(HOST_BUILD_DIR)/libbpf
+	   | $(HOST_BUILD_DIR)/libbpf
 	$(Q)$(MAKE) $(submake_extras) -C $(BPFDIR)                             \
 		    EXTRA_CFLAGS='-g -O0'				       \
 		    OUTPUT=$(HOST_BUILD_DIR)/libbpf/ CC=$(HOSTCC) LD=$(HOSTLD) \
@@ -260,6 +262,7 @@ $(RESOLVE_BTFIDS): $(HOST_BPFOBJ) | $(HOST_BUILD_DIR)/resolve_btfids	\
 		       $(TOOLSDIR)/lib/str_error_r.c
 	$(Q)$(MAKE) $(submake_extras) -C $(TOOLSDIR)/bpf/resolve_btfids	\
 		CC=$(HOSTCC) LD=$(HOSTLD) AR=$(HOSTAR) \
+		LIBBPF_INCLUDE=$(HOST_INCLUDE_DIR) \
 		OUTPUT=$(HOST_BUILD_DIR)/resolve_btfids/ BPFOBJ=$(HOST_BPFOBJ)
 
 # Get Clang's default includes on this system, as opposed to those seen by