perf build: Check LLVM version in feature check

Cancel builtin llvm and clang support when LLVM version is less than
3.9.0: following commits uses newer API.

Since Clang/LLVM's API is not guaranteed to be stable, add a
test-llvm-version.cpp feature checker, issue warning if LLVM found in
compiling environment is not tested yet.

Committer Notes:

Testing it:

Environment:

$ cat /etc/fedora-release
Fedora release 25 (Twenty Five)
$ rpm -q llvm-devel clang-devel
llvm-devel-3.8.0-1.fc25.x86_64
clang-devel-3.8.0-2.fc25.x86_64
$

Before:

$ make -k LIBCLANGLLVM=1 O=/tmp/build/perf -C tools/perf install-bin
make: Entering directory '/home/acme/git/linux/tools/perf'
BUILD: Doing 'make -j4' parallel build
Warning: tools/include/uapi/linux/bpf.h differs from kernel
Warning: tools/arch/arm/include/uapi/asm/kvm.h differs from kernel
INSTALL GTK UI
LINK /tmp/build/perf/perf
/tmp/build/perf/libperf.a(libperf-in.o): In function `perf::createCompilerInvocation(llvm::SmallVector<char const*, 16u>, llvm::StringRef&, clang::DiagnosticsEngine&)':
/home/acme/git/linux/tools/perf/util/c++/clang.cpp:56: undefined reference to `clang::tooling::newInvocation(clang::DiagnosticsEngine*, llvm::SmallVector<char const*, 16u> const&)'
/tmp/build/perf/libperf.a(libperf-in.o): In function `perf::getModuleFromSource(llvm::SmallVector<char const*, 16u>, llvm::StringRef, llvm::IntrusiveRefCntPtr<clang::vfs::FileSystem>)':
/home/acme/git/linux/tools/perf/util/c++/clang.cpp:68: undefined reference to `clang::CompilerInstance::CompilerInstance(std::shared_ptr<clang::PCHContainerOperations>, bool)'
/home/acme/git/linux/tools/perf/util/c++/clang.cpp:69: undefined reference to `clang::CompilerInstance::createDiagnostics(clang::DiagnosticConsumer*, bool)'
<SNIP>

After:

Makefile.config:807: No suitable libLLVM found, disabling builtin clang and llvm support. Please install llvm-dev(el) (>= 3.9.0)

Updating the environment to a locally built LLVM 4.0 + clang 3.9 (forgot
to git pull, duh) combo, all works as expected, it is properly detected
and built into the resulting perf binary.

Signed-off-by: Wang Nan <[e-mail]>
Reported-and-Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Alexei Starovoitov <[e-mail]>
Cc: He Kuang <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Joe Stringer <[e-mail]>
Cc: Zefan Li <[e-mail]>
Cc: [e-mail]
Link: http://lkml.kernel.org/r/[e-mail]
[ Change the warning message a bit (add 'suitable' and 'builtin'), clarifying it, see committer notes above ]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/build/feature/Makefile

···
 	$(BUILD)
 
 $(OUTPUT)test-llvm.bin:
-	$(BUILDXX) -std=gnu++11 					\
+	$(BUILDXX) -std=gnu++11 				\
 		-I$(shell $(LLVM_CONFIG) --includedir) 		\
 		-L$(shell $(LLVM_CONFIG) --libdir)		\
 		$(shell $(LLVM_CONFIG) --libs Core BPF)		\
 		$(shell $(LLVM_CONFIG) --system-libs)
 
+$(OUTPUT)test-llvm-version.bin:
+	$(BUILDXX) -std=gnu++11 				\
+		-I$(shell $(LLVM_CONFIG) --includedir)
+
 $(OUTPUT)test-clang.bin:
-	$(BUILDXX) -std=gnu++11 					\
+	$(BUILDXX) -std=gnu++11 				\
 		-I$(shell $(LLVM_CONFIG) --includedir) 		\
 		-L$(shell $(LLVM_CONFIG) --libdir)		\
 		-Wl,--start-group -lclangBasic -lclangDriver	\

tools/build/feature/test-llvm-version.cpp

···
+#include <cstdio>
+#include "llvm/Config/llvm-config.h"
+
+#define NUM_VERSION (((LLVM_VERSION_MAJOR) << 16) + (LLVM_VERSION_MINOR << 8) + LLVM_VERSION_PATCH)
+#define pass int main() {printf("%x\n", NUM_VERSION); return 0;}
+
+#if NUM_VERSION >= 0x030900
+pass
+#else
+# error This LLVM is not tested yet.
+#endif

tools/build/feature/test-llvm.cpp

···
 #include "llvm/Support/ManagedStatic.h"
 #include "llvm/Support/raw_ostream.h"
+#define NUM_VERSION (((LLVM_VERSION_MAJOR) << 16) + (LLVM_VERSION_MINOR << 8) + LLVM_VERSION_PATCH)
+
+#if NUM_VERSION < 0x030900
+# error "LLVM version too low"
+#endif
 int main()
 {
 	llvm::errs() << "Hello World!\n";

tools/perf/Makefile.config

···
     msg := $(warning No g++ found, disable clang and llvm support. Please install g++)
   else
     $(call feature_check,llvm)
+    $(call feature_check,llvm-version)
     ifneq ($(feature-llvm), 1)
-      msg := $(warning No libLLVM found, disable clang and llvm support. Please install llvm-dev)
+      msg := $(warning No suitable libLLVM found, disabling builtin clang and LLVM support. Please install llvm-dev(el) (>= 3.9.0))
     else
       $(call feature_check,clang)
       ifneq ($(feature-clang), 1)
-        msg := $(warning No libclang found, disable clang and llvm support. Please install libclang-dev)
+        msg := $(warning No suitable libclang found, disabling builtin clang and LLVM support. Please install libclang-dev(el) (>= 3.9.0))
       else
         CFLAGS += -DHAVE_LIBCLANGLLVM_SUPPORT
         CXXFLAGS += -DHAVE_LIBCLANGLLVM_SUPPORT -I$(shell $(LLVM_CONFIG) --includedir)
···
 	USE_CXX = 1
 	USE_LLVM = 1
 	USE_CLANG = 1
+        ifneq ($(feature-llvm-version),1)
+          msg := $(warning This version of LLVM is not tested. May cause build errors)
+        endif
       endif
     endif
   endif