[tip:perf/core] tools build: Add feature detection for clang

[tip-bot for Wang Nan]

Commit-ID:  c7fb4f62e2a97bd25d555263ef501fe053edcbb6
Gitweb:     http://git.kernel.org/tip/c7fb4f62e2a97bd25d555263ef501fe053edcbb6
Author:     Wang Nan <wangnan0@xxxxxxxxxx>
AuthorDate: Sat, 26 Nov 2016 07:03:32 +0000
Committer:  Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitDate: Mon, 5 Dec 2016 15:51:43 -0300

tools build: Add feature detection for clang

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: Alexei Starovoitov <ast@xxxxxx>
Cc: He Kuang <hekuang@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Joe Stringer <joe@xxxxxxx>
Cc: Zefan Li <lizefan@xxxxxxxxxx>
Cc: pi3orama@xxxxxxx
Link: http://lkml.kernel.org/r/20161126070354.141764-9-wangnan0@xxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/build/feature/Makefile       | 10 ++++++++++
 tools/build/feature/test-clang.cpp | 21 +++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/tools/build/feature/Makefile b/tools/build/feature/Makefile
index c09de59..871d553 100644
--- a/tools/build/feature/Makefile
+++ b/tools/build/feature/Makefile
@@ -237,6 +237,16 @@ $(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;
+}