perf clang: Support compile IR to BPF object and add testcase

getBPFObjectFromModule() is introduced to compile LLVM IR(Module)
to BPF object. Add new testcase for it.

Test result:
  $ ./buildperf/perf test -v clang
  51: builtin clang support                               :
  51.1: builtin clang compile C source to IR              :
  --- start ---
  test child forked, pid 21822
  test child finished with 0
  ---- end ----
  builtin clang support subtest 0: Ok
  51.2: builtin clang compile C source to ELF object      :
  --- start ---
  test child forked, pid 21823
  test child finished with 0
  ---- end ----
  builtin clang support subtest 1: Ok
Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: Alexei Starovoitov <ast@fb.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Joe Stringer <joe@ovn.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/20161126070354.141764-15-wangnan0@huawei.com
[ Remove redundant "Test" from entry descriptions ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/clang.c

@@ -12,6 +12,10 @@ static struct {
 		.func = test__clang_to_IR,
 		.desc = "builtin clang compile C source to IR",
 	},
+	{
+		.func = test__clang_to_obj,
+		.desc = "builtin clang compile C source to ELF object",
+	},
 #endif
 };
 
@@ -33,7 +37,7 @@ int test__clang(int i __maybe_unused)
 	return TEST_SKIP;
 }
 #else
-int test__clang(int i __maybe_unused)
+int test__clang(int i)
 {
 	if (i < 0 || i >= (int)ARRAY_SIZE(clang_testcase_table))
 		return TEST_FAIL;

tools/perf/util/c++/clang-c.h

@@ -9,6 +9,7 @@ extern void perf_clang__init(void);
 extern void perf_clang__cleanup(void);
 
 extern int test__clang_to_IR(void);
+extern int test__clang_to_obj(void);
 
 #ifdef __cplusplus
 }

tools/perf/util/c++/clang-test.cpp

@@ -13,15 +13,13 @@ public:
 	~perf_clang_scope() {perf_clang__cleanup();}
 };
 
-extern "C" {
-
-int test__clang_to_IR(void)
+static std::unique_ptr<llvm::Module>
+__test__clang_to_IR(void)
 {
-	perf_clang_scope _scope;
 	unsigned int kernel_version;
 
 	if (fetch_kernel_version(&kernel_version, NULL, 0))
-		return -1;
+		return std::unique_ptr<llvm::Module>(nullptr);
 
 	std::string cflag_kver("-DLINUX_VERSION_CODE=" +
 				std::to_string(kernel_version));
@@ -30,14 +28,35 @@ int test__clang_to_IR(void)
 		perf::getModuleFromSource({cflag_kver.c_str()},
 					  "perf-test.c",
 					  test_llvm__bpf_base_prog);
+	return M;
+}
+
+extern "C" {
+int test__clang_to_IR(void)
+{
+	perf_clang_scope _scope;
 
+	auto M = __test__clang_to_IR();
 	if (!M)
 		return -1;
-
 	for (llvm::Function& F : *M)
 		if (F.getName() == "bpf_func__SyS_epoll_wait")
 			return 0;
 	return -1;
 }
 
+int test__clang_to_obj(void)
+{
+	perf_clang_scope _scope;
+
+	auto M = __test__clang_to_IR();
+	if (!M)
+		return -1;
+
+	auto Buffer = perf::getBPFObjectFromModule(&*M);
+	if (!Buffer)
+		return -1;
+	return 0;
+}
+
 }

tools/perf/util/c++/clang.cpp

@@ -13,10 +13,15 @@
 #include "clang/Frontend/CompilerInstance.h"
 #include "clang/Frontend/TextDiagnosticPrinter.h"
 #include "clang/Tooling/Tooling.h"
+#include "llvm/IR/LegacyPassManager.h"
 #include "llvm/IR/Module.h"
 #include "llvm/Option/Option.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/ManagedStatic.h"
+#include "llvm/Support/TargetRegistry.h"
+#include "llvm/Support/TargetSelect.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/Target/TargetOptions.h"
 #include <memory>
 
 #include "clang.h"
@@ -105,12 +110,52 @@ getModuleFromSource(llvm::opt::ArgStringList CFlags, StringRef Path)
 	return getModuleFromSource(std::move(CFlags), Path, VFS);
 }
 
+std::unique_ptr<llvm::SmallVectorImpl<char>>
+getBPFObjectFromModule(llvm::Module *Module)
+{
+	using namespace llvm;
+
+	std::string TargetTriple("bpf-pc-linux");
+	std::string Error;
+	const Target* Target = TargetRegistry::lookupTarget(TargetTriple, Error);
+	if (!Target) {
+		llvm::errs() << Error;
+		return std::unique_ptr<llvm::SmallVectorImpl<char>>(nullptr);
+	}
+
+	llvm::TargetOptions Opt;
+	TargetMachine *TargetMachine =
+		Target->createTargetMachine(TargetTriple,
+					    "generic", "",
+					    Opt, Reloc::Static);
+
+	Module->setDataLayout(TargetMachine->createDataLayout());
+	Module->setTargetTriple(TargetTriple);
+
+	std::unique_ptr<SmallVectorImpl<char>> Buffer(new SmallVector<char, 0>());
+	raw_svector_ostream ostream(*Buffer);
+
+	legacy::PassManager PM;
+	if (TargetMachine->addPassesToEmitFile(PM, ostream,
+					       TargetMachine::CGFT_ObjectFile)) {
+		llvm::errs() << "TargetMachine can't emit a file of this type\n";
+		return std::unique_ptr<llvm::SmallVectorImpl<char>>(nullptr);;
+	}
+	PM.run(*Module);
+
+	return std::move(Buffer);
+}
+
 }
 
 extern "C" {
 void perf_clang__init(void)
 {
 	perf::LLVMCtx.reset(new llvm::LLVMContext());
+	LLVMInitializeBPFTargetInfo();
+	LLVMInitializeBPFTarget();
+	LLVMInitializeBPFTargetMC();
+	LLVMInitializeBPFAsmPrinter();
 }
 
 void perf_clang__cleanup(void)

tools/perf/util/c++/clang.h

@@ -19,5 +19,8 @@ std::unique_ptr<Module>
 getModuleFromSource(opt::ArgStringList CFlags,
 		    StringRef Path);
 
+std::unique_ptr<llvm::SmallVectorImpl<char>>
+getBPFObjectFromModule(llvm::Module *Module);
+
 }
 #endif