samples/bpf: Clean up samples/bpf build failes

Remove xdp_samples_user.o rule redefinition which generates Makefile
warning and instead override TPROGS_CFLAGS. This seems to work fine when
building inside selftests/bpf.

That was one big head-scratcher before I found that generic
Makefile.target hid this surprising specialization for for xdp_samples_user.o.

Main change is to use actual locally installed libbpf headers.

Also drop printk macro re-definition (not even used!).

Signed-off-by: Andrii Nakryiko <[e-mail]>
Signed-off-by: Alexei Starovoitov <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

samples/bpf/Makefile

···
 $(src)/*.c: verify_target_bpf $(LIBBPF)
 
 libbpf_hdrs: $(LIBBPF)
-$(obj)/$(TRACE_HELPERS): | libbpf_hdrs
+$(obj)/$(TRACE_HELPERS) $(obj)/$(CGROUP_HELPERS) $(obj)/$(XDP_SAMPLE): | libbpf_hdrs
 
 .PHONY: libbpf_hdrs
 
···
 $(obj)/hbm_out_kern.o: $(src)/hbm.h $(src)/hbm_kern.h
 $(obj)/hbm.o: $(src)/hbm.h
 $(obj)/hbm_edt_kern.o: $(src)/hbm.h $(src)/hbm_kern.h
+
+# Override includes for xdp_sample_user.o because $(srctree)/usr/include in
+# TPROGS_CFLAGS causes conflicts
+XDP_SAMPLE_CFLAGS += -Wall -O2 -lm \
+		     -I$(src)/../../tools/include \
+		     -I$(src)/../../tools/include/uapi \
+		     -I$(LIBBPF_INCLUDE) \
+		     -I$(src)/../../tools/testing/selftests/bpf
+
+$(obj)/$(XDP_SAMPLE): TPROGS_CFLAGS = $(XDP_SAMPLE_CFLAGS)
+$(obj)/$(XDP_SAMPLE): $(src)/xdp_sample_user.h $(src)/xdp_sample_shared.h
 
 -include $(BPF_SAMPLES_PATH)/Makefile.target
 

samples/bpf/Makefile.target

···
       cmd_tprog-cobjs	= $(CC) $(tprogc_flags) -c -o $@ $<
 $(tprog-cobjs): $(obj)/%.o: $(src)/%.c FORCE
 	$(call if_changed_dep,tprog-cobjs)
-
-# Override includes for xdp_sample_user.o because $(srctree)/usr/include in
-# TPROGS_CFLAGS causes conflicts
-XDP_SAMPLE_CFLAGS += -Wall -O2 -lm \
-		     -I./tools/include \
-		     -I./tools/include/uapi \
-		     -I./tools/lib \
-		     -I./tools/testing/selftests/bpf
-$(obj)/xdp_sample_user.o: $(src)/xdp_sample_user.c \
-	$(src)/xdp_sample_user.h $(src)/xdp_sample_shared.h
-	$(CC) $(XDP_SAMPLE_CFLAGS) -c -o $@ $<

samples/bpf/hbm_kern.h

···
  * Include file for sample Host Bandwidth Manager (HBM) BPF programs
  */
 #define KBUILD_MODNAME "foo"
-#include <stddef.h>
-#include <stdbool.h>
 #include <uapi/linux/bpf.h>
 #include <uapi/linux/if_ether.h>
 #include <uapi/linux/if_packet.h>

samples/bpf/lwt_len_hist_kern.c

···
 #include <uapi/linux/in.h>
 #include <bpf/bpf_helpers.h>
 
-# define printk(fmt, ...)						\
-		({							\
-			char ____fmt[] = fmt;				\
-			bpf_trace_printk(____fmt, sizeof(____fmt),	\
-				     ##__VA_ARGS__);			\
-		})
-
 struct bpf_elf_map {
 	__u32 type;
 	__u32 size_key;