perf build: Fix build error when NO_LIBBPF=1

The $(LIBBPF) target should only be a dependency of prepare if the
static version of libbpf is needed. Add a new LIBBPF_STATIC variable
that is set by Makefile.config. Use LIBBPF_STATIC to determine whether
the CFLAGS, etc. need updating and for adding $(LIBBPF) as a prepare
dependency.

As Makefile.config isn't loaded for "clean" as a target, always set
LIBBPF_OUTPUT regardless of whether it is needed for $(LIBBPF). This
is done to minimize conditional logic for $(LIBBPF)-clean.

This issue and an original fix was reported by Mike Leach in:
https://lore.kernel.org/lkml/[email protected]/

Fixes: 746bd29 ("perf build: Use tools/lib headers from install path")
Reported-by: Mike Leach <[email protected]>
Signed-off-by: Ian Rogers <[email protected]>
Tested-by: Jiri Olsa <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: [email protected]
Cc: Ian Rogers <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: http://lore.kernel.org/lkml/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

tools/perf/Makefile.config

@@ -602,6 +602,8 @@ ifndef NO_LIBELF
           dummy := $(error Error: No libbpf devel library found, please install libbpf-devel);
         endif
       else
+        # Libbpf will be built as a static library from tools/lib/bpf.
+	LIBBPF_STATIC := 1
 	CFLAGS += -DHAVE_LIBBPF_BTF__LOAD_FROM_KERNEL_BY_ID
         CFLAGS += -DHAVE_LIBBPF_BPF_PROG_LOAD
         CFLAGS += -DHAVE_LIBBPF_BPF_OBJECT__NEXT_PROGRAM

tools/perf/Makefile.perf

@@ -303,10 +303,12 @@ ifneq ($(OUTPUT),)
 else
   LIBBPF_OUTPUT = $(CURDIR)/libbpf
 endif
-LIBBPF_DESTDIR = $(LIBBPF_OUTPUT)
-LIBBPF_INCLUDE = $(LIBBPF_DESTDIR)/include
-LIBBPF = $(LIBBPF_OUTPUT)/libbpf.a
-CFLAGS += -I$(LIBBPF_OUTPUT)/include
+ifdef LIBBPF_STATIC
+  LIBBPF_DESTDIR = $(LIBBPF_OUTPUT)
+  LIBBPF_INCLUDE = $(LIBBPF_DESTDIR)/include
+  LIBBPF = $(LIBBPF_OUTPUT)/libbpf.a
+  CFLAGS += -I$(LIBBPF_OUTPUT)/include
+endif
 
 ifneq ($(OUTPUT),)
   LIBSUBCMD_OUTPUT = $(abspath $(OUTPUT))/libsubcmd
@@ -393,10 +395,8 @@ endif
 export PERL_PATH
 
 PERFLIBS = $(LIBAPI) $(LIBPERF) $(LIBSUBCMD) $(LIBSYMBOL)
-ifndef NO_LIBBPF
-  ifndef LIBBPF_DYNAMIC
-    PERFLIBS += $(LIBBPF)
-  endif
+ifdef LIBBPF_STATIC
+  PERFLIBS += $(LIBBPF)
 endif
 
 # We choose to avoid "if .. else if .. else .. endif endif"
@@ -756,12 +756,15 @@ prepare: $(OUTPUT)PERF-VERSION-FILE $(OUTPUT)common-cmds.h archheaders $(drm_ioc
 	$(arch_errno_name_array) \
 	$(sync_file_range_arrays) \
 	$(LIBAPI) \
-	$(LIBBPF) \
 	$(LIBPERF) \
 	$(LIBSUBCMD) \
 	$(LIBSYMBOL) \
 	bpf-skel
 
+ifdef LIBBPF_STATIC
+prepare: $(LIBBPF)
+endif
+
 $(OUTPUT)%.o: %.c prepare FORCE
 	$(Q)$(MAKE) -f $(srctree)/tools/build/Makefile.build dir=$(build-dir) $@