bpf: btf: Add BTF tests

This patch tests the BTF loading, map_create with BTF
and the changes in libbpf.

-r: Raw tests that test raw crafted BTF data
-f: Test LLVM compiled bpf prog with BTF data
-g: Test BPF_OBJ_GET_INFO_BY_FD for btf_fd
-p: Test pretty print

The tools/testing/selftests/bpf/Makefile will probe
for BTF support in llc and pahole before generating
debug info (-g) and convert them to BTF.  You can supply
the BTF supported binary through the following make variables:
LLC, BTF_PAHOLE and LLVM_OBJCOPY.

LLC: The lastest llc with -mattr=dwarfris support for the bpf target.
     It is only in the master of the llvm repo for now.
BTF_PAHOLE: The modified pahole with BTF support:
	    https://github.com/iamkafai/pahole/tree/btf
	    To add a BTF section: "pahole -J bpf_prog.o"
LLVM_OBJCOPY: Any llvm-objcopy should do

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Alexei Starovoitov <ast@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/testing/selftests/bpf/Makefile

@@ -24,14 +24,15 @@ urandom_read: urandom_read.c
 # Order correspond to 'make run_tests' order
 TEST_GEN_PROGS = test_verifier test_tag test_maps test_lru_map test_lpm_map test_progs \
 	test_align test_verifier_log test_dev_cgroup test_tcpbpf_user \
-	test_sock test_sock_addr
+	test_sock test_sock_addr test_btf
 
 TEST_GEN_FILES = test_pkt_access.o test_xdp.o test_l4lb.o test_tcp_estats.o test_obj_id.o \
 	test_pkt_md_access.o test_xdp_redirect.o test_xdp_meta.o sockmap_parse_prog.o     \
 	sockmap_verdict_prog.o dev_cgroup.o sample_ret0.o test_tracepoint.o \
 	test_l4lb_noinline.o test_xdp_noinline.o test_stacktrace_map.o \
 	sample_map_ret0.o test_tcpbpf_kern.o test_stacktrace_build_id.o \
-	sockmap_tcp_msg_prog.o connect4_prog.o connect6_prog.o test_adjust_tail.o
+	sockmap_tcp_msg_prog.o connect4_prog.o connect6_prog.o test_adjust_tail.o \
+	test_btf_haskv.o test_btf_nokv.o
 
 # Order correspond to 'make run_tests' order
 TEST_PROGS := test_kmod.sh \
@@ -66,6 +67,8 @@ $(BPFOBJ): force
 
 CLANG ?= clang
 LLC   ?= llc
+LLVM_OBJCOPY ?= llvm-objcopy
+BTF_PAHOLE ?= pahole
 
 PROBE := $(shell $(LLC) -march=bpf -mcpu=probe -filetype=null /dev/null 2>&1)
 
@@ -83,9 +86,26 @@ CLANG_FLAGS = -I. -I./include/uapi -I../../../include/uapi \
 $(OUTPUT)/test_l4lb_noinline.o: CLANG_FLAGS += -fno-inline
 $(OUTPUT)/test_xdp_noinline.o: CLANG_FLAGS += -fno-inline
 
+BTF_LLC_PROBE := $(shell $(LLC) -march=bpf -mattr=help |& grep dwarfris)
+BTF_PAHOLE_PROBE := $(shell $(BTF_PAHOLE) --help |& grep BTF)
+BTF_OBJCOPY_PROBE := $(shell $(LLVM_OBJCOPY) --version |& grep LLVM)
+
+ifneq ($(BTF_LLC_PROBE),)
+ifneq ($(BTF_PAHOLE_PROBE),)
+ifneq ($(BTF_OBJCOPY_PROBE),)
+	CLANG_FLAGS += -g
+	LLC_FLAGS += -mattr=dwarfris
+	DWARF2BTF = y
+endif
+endif
+endif
+
 $(OUTPUT)/%.o: %.c
 	$(CLANG) $(CLANG_FLAGS) \
 		 -O2 -target bpf -emit-llvm -c $< -o - |      \
-	$(LLC) -march=bpf -mcpu=$(CPU) -filetype=obj -o $@
+	$(LLC) -march=bpf -mcpu=$(CPU) $(LLC_FLAGS) -filetype=obj -o $@
+ifeq ($(DWARF2BTF),y)
+	$(BTF_PAHOLE) -J $@
+endif
 
 EXTRA_CLEAN := $(TEST_CUSTOM_PROGS)