bpf, libbpf: fix version info and add it to shared object

Even though libbpf's versioning script for the linker (libbpf.map)
is pointing to 0.0.2, the BPF_EXTRAVERSION in the Makefile has
not been updated along with it and is therefore still on 0.0.1.

While fixing up, I also noticed that the generated shared object
versioning information is missing, typical convention is to have
a linker name (libbpf.so), soname (libbpf.so.0) and real name
(libbpf.so.0.0.2) for library management. This is based upon the
LIBBPF_VERSION as well.

The build will then produce the following bpf libraries:

  # ll libbpf*
  libbpf.a
  libbpf.so -> libbpf.so.0.0.2
  libbpf.so.0 -> libbpf.so.0.0.2
  libbpf.so.0.0.2

  # readelf -d libbpf.so.0.0.2 | grep SONAME
  0x000000000000000e (SONAME)             Library soname: [libbpf.so.0]

And install them accordingly:

  # rm -rf /tmp/bld; mkdir /tmp/bld; make -j$(nproc) O=/tmp/bld install

  Auto-detecting system features:
  ...                        libelf: [ on  ]
  ...                           bpf: [ on  ]

    CC       /tmp/bld/libbpf.o
    CC       /tmp/bld/bpf.o
    CC       /tmp/bld/nlattr.o
    CC       /tmp/bld/btf.o
    CC       /tmp/bld/libbpf_errno.o
    CC       /tmp/bld/str_error.o
    CC       /tmp/bld/netlink.o
    CC       /tmp/bld/bpf_prog_linfo.o
    CC       /tmp/bld/libbpf_probes.o
    CC       /tmp/bld/xsk.o
    LD       /tmp/bld/libbpf-in.o
    LINK     /tmp/bld/libbpf.a
    LINK     /tmp/bld/libbpf.so.0.0.2
    LINK     /tmp/bld/test_libbpf
    INSTALL  /tmp/bld/libbpf.a
    INSTALL  /tmp/bld/libbpf.so.0.0.2

  # ll /usr/local/lib64/libbpf.*
  /usr/local/lib64/libbpf.a
  /usr/local/lib64/libbpf.so -> libbpf.so.0.0.2
  /usr/local/lib64/libbpf.so.0 -> libbpf.so.0.0.2
  /usr/local/lib64/libbpf.so.0.0.2

Fixes: 1bf4b058 ("tools: bpftool: add probes for eBPF program types")
Fixes: 1b76c13e ("bpf tools: Introduce 'bpf' library and add bpf feature check")
Reported-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/lib/bpf/Makefile

@@ -3,7 +3,7 @@
 
 BPF_VERSION = 0
 BPF_PATCHLEVEL = 0
-BPF_EXTRAVERSION = 1
+BPF_EXTRAVERSION = 2
 
 MAKEFLAGS += --no-print-directory
 
@@ -79,8 +79,6 @@ export prefix libdir src obj
 libdir_SQ = $(subst ','\'',$(libdir))
 libdir_relative_SQ = $(subst ','\'',$(libdir_relative))
 
-LIB_FILE = libbpf.a libbpf.so
-
 VERSION		= $(BPF_VERSION)
 PATCHLEVEL	= $(BPF_PATCHLEVEL)
 EXTRAVERSION	= $(BPF_EXTRAVERSION)
@@ -90,6 +88,9 @@ N		=
 
 LIBBPF_VERSION	= $(BPF_VERSION).$(BPF_PATCHLEVEL).$(BPF_EXTRAVERSION)
 
+LIB_TARGET	= libbpf.a libbpf.so.$(LIBBPF_VERSION)
+LIB_FILE	= libbpf.a libbpf.so*
+
 # Set compile option CFLAGS
 ifdef EXTRA_CFLAGS
   CFLAGS := $(EXTRA_CFLAGS)
@@ -129,15 +130,17 @@ export srctree OUTPUT CC LD CFLAGS V
 include $(srctree)/tools/build/Makefile.include
 
 BPF_IN		:= $(OUTPUT)libbpf-in.o
-LIB_FILE := $(addprefix $(OUTPUT),$(LIB_FILE))
 VERSION_SCRIPT	:= libbpf.map
 
+LIB_TARGET	:= $(addprefix $(OUTPUT),$(LIB_TARGET))
+LIB_FILE	:= $(addprefix $(OUTPUT),$(LIB_FILE))
+
 GLOBAL_SYM_COUNT = $(shell readelf -s --wide $(BPF_IN) | \
 			   awk '/GLOBAL/ && /DEFAULT/ && !/UND/ {s++} END{print s}')
 VERSIONED_SYM_COUNT = $(shell readelf -s --wide $(OUTPUT)libbpf.so | \
 			      grep -Eo '[^ ]+@LIBBPF_' | cut -d@ -f1 | sort -u | wc -l)
 
-CMD_TARGETS = $(LIB_FILE)
+CMD_TARGETS = $(LIB_TARGET)
 
 CXX_TEST_TARGET = $(OUTPUT)test_libbpf
 
@@ -170,9 +173,13 @@ $(BPF_IN): force elfdep bpfdep
 	echo "Warning: Kernel ABI header at 'tools/include/uapi/linux/if_xdp.h' differs from latest version at 'include/uapi/linux/if_xdp.h'" >&2 )) || true
 	$(Q)$(MAKE) $(build)=libbpf
 
-$(OUTPUT)libbpf.so: $(BPF_IN)
-	$(QUIET_LINK)$(CC) --shared -Wl,--version-script=$(VERSION_SCRIPT) \
-		$^ -o $@
+$(OUTPUT)libbpf.so: $(OUTPUT)libbpf.so.$(LIBBPF_VERSION)
+
+$(OUTPUT)libbpf.so.$(LIBBPF_VERSION): $(BPF_IN)
+	$(QUIET_LINK)$(CC) --shared -Wl,-soname,libbpf.so.$(VERSION) \
+				    -Wl,--version-script=$(VERSION_SCRIPT) $^ -o $@
+	@ln -sf $(@F) $(OUTPUT)libbpf.so
+	@ln -sf $(@F) $(OUTPUT)libbpf.so.$(VERSION)
 
 $(OUTPUT)libbpf.a: $(BPF_IN)
 	$(QUIET_LINK)$(RM) $@; $(AR) rcs $@ $^
@@ -192,6 +199,12 @@ check_abi: $(OUTPUT)libbpf.so
 		exit 1;							 \
 	fi
 
+define do_install_mkdir
+	if [ ! -d '$(DESTDIR_SQ)$1' ]; then		\
+		$(INSTALL) -d -m 755 '$(DESTDIR_SQ)$1';	\
+	fi
+endef
+
 define do_install
 	if [ ! -d '$(DESTDIR_SQ)$2' ]; then		\
 		$(INSTALL) -d -m 755 '$(DESTDIR_SQ)$2';	\
@@ -200,8 +213,9 @@ define do_install
 endef
 
 install_lib: all_cmd
-	$(call QUIET_INSTALL, $(LIB_FILE)) \
-		$(call do_install,$(LIB_FILE),$(libdir_SQ))
+	$(call QUIET_INSTALL, $(LIB_TARGET)) \
+		$(call do_install_mkdir,$(libdir_SQ)); \
+		cp -fpR $(LIB_FILE) $(DESTDIR)$(libdir_SQ)
 
 install_headers:
 	$(call QUIET_INSTALL, headers) \
@@ -219,7 +233,7 @@ config-clean:
 
 clean:
 	$(call QUIET_CLEAN, libbpf) $(RM) $(TARGETS) $(CXX_TEST_TARGET) \
-		*.o *~ *.a *.so .*.d .*.cmd LIBBPF-CFLAGS
+		*.o *~ *.a *.so *.so.$(VERSION) .*.d .*.cmd LIBBPF-CFLAGS
 	$(call QUIET_CLEAN, core-gen) $(RM) $(OUTPUT)FEATURE-DUMP.libbpf