From: Stanislav Fomichev <sdf@google.com>
Date: Mon, 2 Dec 2019 13:59:31 -0800
Subject: selftests/bpf: Bring back c++ include/link test
Patch-mainline: v5.5-rc1
Git-commit: 6bf6affe18dafea6ef12036001162ac7f2dbf738
References: bsc#1177028

Commit 5c26f9a78358 ("libbpf: Don't use cxx to test_libpf target")
converted existing c++ test to c. We still want to include and
link against libbpf from c++ code, so reinstate this test back,
this time in a form of a selftest with a clear comment about
its purpose.

v2:
* -lelf -> $(LDLIBS) (Andrii Nakryiko)

Fixes: 5c26f9a78358 ("libbpf: Don't use cxx to test_libpf target")
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20191202215931.248178-1-sdf@google.com
Acked-by: Gary Lin <glin@suse.com>
---
 tools/lib/bpf/.gitignore                                    | 1 -
 tools/lib/bpf/Makefile                                      | 5 +----
 tools/testing/selftests/bpf/.gitignore                      | 1 +
 tools/testing/selftests/bpf/Makefile                        | 6 +++++-
 .../test_libbpf.c => testing/selftests/bpf/test_cpp.cpp}    | 0
 tools/lib/bpf/.gitignore                 |    1 -
 tools/lib/bpf/Makefile                   |    5 +----
 tools/lib/bpf/test_libbpf.c              |   20 --------------------
 tools/testing/selftests/bpf/.gitignore   |    1 +
 tools/testing/selftests/bpf/Makefile     |    6 +++++-
 tools/testing/selftests/bpf/test_cpp.cpp |   20 ++++++++++++++++++++
 6 files changed, 27 insertions(+), 26 deletions(-)
 rename tools/{lib/bpf/test_libbpf.c => testing/selftests/bpf/test_cpp.cpp} (100%)

--- a/tools/lib/bpf/.gitignore
+++ b/tools/lib/bpf/.gitignore
@@ -1,7 +1,6 @@
 libbpf_version.h
 libbpf.pc
 FEATURE-DUMP.libbpf
-test_libbpf
 libbpf.so.*
 TAGS
 tags
--- a/tools/lib/bpf/Makefile
+++ b/tools/lib/bpf/Makefile
@@ -148,7 +148,7 @@ GLOBAL_SYM_COUNT = $(shell readelf -s --
 VERSIONED_SYM_COUNT = $(shell readelf -s --wide $(OUTPUT)libbpf.so | \
 			      grep -Eo '[^ ]+@LIBBPF_' | cut -d@ -f1 | sort -u | wc -l)
 
-CMD_TARGETS = $(LIB_TARGET) $(PC_FILE) $(OUTPUT)test_libbpf
+CMD_TARGETS = $(LIB_TARGET) $(PC_FILE)
 
 all: fixdep
 	$(Q)$(MAKE) all_cmd
@@ -192,9 +192,6 @@ $(OUTPUT)libbpf.so.$(LIBBPF_VERSION): $(
 $(OUTPUT)libbpf.a: $(BPF_IN_STATIC)
 	$(QUIET_LINK)$(RM) $@; $(AR) rcs $@ $^
 
-$(OUTPUT)test_libbpf: test_libbpf.c $(OUTPUT)libbpf.a
-	$(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) $(INCLUDES) $^ -lelf -o $@
-
 $(OUTPUT)libbpf.pc:
 	$(QUIET_GEN)sed -e "s|@PREFIX@|$(prefix)|" \
 		-e "s|@LIBDIR@|$(libdir_SQ)|" \
--- a/tools/lib/bpf/test_libbpf.c
+++ /dev/null
@@ -1,20 +0,0 @@
-/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
-#include "libbpf.h"
-#include "bpf.h"
-#include "btf.h"
-
-/* do nothing, just make sure we can link successfully */
-
-int main(int argc, char *argv[])
-{
-	/* libbpf.h */
-	libbpf_set_print(NULL);
-
-	/* bpf.h */
-	bpf_prog_get_fd_by_id(0);
-
-	/* btf.h */
-	btf__new(NULL, 0);
-
-	return 0;
-}
--- a/tools/testing/selftests/bpf/.gitignore
+++ b/tools/testing/selftests/bpf/.gitignore
@@ -37,5 +37,6 @@ libbpf.so.*
 test_hashmap
 test_btf_dump
 xdping
+test_cpp
 /no_alu32
 /bpf_gcc
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -71,7 +71,7 @@ TEST_PROGS_EXTENDED := with_addr.sh \
 # Compile but not part of 'make run_tests'
 TEST_GEN_PROGS_EXTENDED = test_sock_addr test_skb_cgroup_id_user \
 	flow_dissector_load test_flow_dissector test_tcp_check_syncookie_user \
-	test_lirc_mode2_user xdping
+	test_lirc_mode2_user xdping test_cpp
 
 TEST_CUSTOM_PROGS = urandom_read
 
@@ -317,6 +317,10 @@ verifier/tests.h: verifier/*.c
 $(OUTPUT)/test_verifier: test_verifier.c verifier/tests.h $(BPFOBJ) | $(OUTPUT)
 	$(CC) $(CFLAGS) $(filter %.a %.o %.c,$^) $(LDLIBS) -o $@
 
+# Make sure we are able to include and link libbpf against c++.
+$(OUTPUT)/test_cpp: test_cpp.cpp $(BPFOBJ)
+	$(CXX) $(CFLAGS) $^ $(LDLIBS) -o $@
+
 EXTRA_CLEAN := $(TEST_CUSTOM_PROGS)					\
 	prog_tests/tests.h map_tests/tests.h verifier/tests.h		\
 	feature $(OUTPUT)/*.o $(OUTPUT)/no_alu32 $(OUTPUT)/bpf_gcc
--- /dev/null
+++ b/tools/testing/selftests/bpf/test_cpp.cpp
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
+#include "libbpf.h"
+#include "bpf.h"
+#include "btf.h"
+
+/* do nothing, just make sure we can link successfully */
+
+int main(int argc, char *argv[])
+{
+	/* libbpf.h */
+	libbpf_set_print(NULL);
+
+	/* bpf.h */
+	bpf_prog_get_fd_by_id(0);
+
+	/* btf.h */
+	btf__new(NULL, 0);
+
+	return 0;
+}