[PATCH v2 04/18] perf tools: Add feature detection for clang

[Wang Nan]

Check if basic clang compiling environment is ready.

Doesn't like 'llvm-config --libs' which can returns llvm libraries in
right order and duplicates some libraries if necessary, there's no
correspondence for clang libraries (-lclangxxx). to avoid extra
complexity and to avoid new clang breaking libraries ordering, use
--start-group and --end-group.

In this test case, manually identify required clang libs and hope it
to be stable. Putting all clang libraries here is possible (use
make's wildcard), but then feature checking becomes very slow.

Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxx>
Cc: He Kuang <hekuang@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
---
 tools/build/feature/Makefile       | 10 ++++++++++
 tools/build/feature/test-clang.cpp | 21 +++++++++++++++++++++
 2 files changed, 31 insertions(+)
 create mode 100644 tools/build/feature/test-clang.cpp

diff --git a/tools/build/feature/Makefile b/tools/build/feature/Makefile
index fd2f3e2..0af90dd 100644
--- a/tools/build/feature/Makefile
+++ b/tools/build/feature/Makefile
@@ -233,6 +233,16 @@ $(OUTPUT)test-llvm.bin:
 		$(shell $(LLVM_CONFIG) --libs Core BPF)		\
 		$(shell $(LLVM_CONFIG) --system-libs)
 
+$(OUTPUT)test-clang.bin:
+	$(BUILDXX) -std=gnu++11 					\
+		-I$(shell $(LLVM_CONFIG) --includedir) 		\
+		-L$(shell $(LLVM_CONFIG) --libdir)		\
+		-Wl,--start-group -lclangBasic -lclangDriver	\
+		  -lclangFrontend -lclangEdit -lclangLex	\
+		  -lclangAST -Wl,--end-group 			\
+		$(shell $(LLVM_CONFIG) --libs Core option)	\
+		$(shell $(LLVM_CONFIG) --system-libs)
+
 -include $(OUTPUT)*.d
 
 ###############################
diff --git a/tools/build/feature/test-clang.cpp b/tools/build/feature/test-clang.cpp
new file mode 100644
index 0000000..e23c1b1
--- /dev/null
+++ b/tools/build/feature/test-clang.cpp
@@ -0,0 +1,21 @@
+#include "clang/Basic/VirtualFileSystem.h"
+#include "clang/Driver/Driver.h"
+#include "clang/Frontend/TextDiagnosticPrinter.h"
+#include "llvm/ADT/IntrusiveRefCntPtr.h"
+#include "llvm/Support/ManagedStatic.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace clang;
+using namespace clang::driver;
+
+int main()
+{
+	IntrusiveRefCntPtr<DiagnosticIDs> DiagID(new DiagnosticIDs());
+	IntrusiveRefCntPtr<DiagnosticOptions> DiagOpts = new DiagnosticOptions();
+
+	DiagnosticsEngine Diags(DiagID, &*DiagOpts);
+	Driver TheDriver("test", "bpf-pc-linux", Diags);
+
+	llvm::llvm_shutdown();
+	return 0;
+}
-- 
1.8.3.4