[PATCH v4 07/18] perf clang jit: Insignt BPF and JIT functions in a Module

[Wang Nan]

Identify BPF functions, JIT functions and maps during init. Functions in
section starting with "perfhook:" are JIT functions. They will be JIT
compiled and hooked at perfhooks.

During init of PerfModule, mark JIT functions as AvailableExternallyLinkage.
LLVM skips functions with linkage like this so they won't be compiled
into BPF objects.

Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
Acked-by: Alexei Starovoitov <ast@xxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: He Kuang <hekuang@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Zefan Li <lizefan@xxxxxxxxxx>
Cc: pi3orama@xxxxxxx
---
 tools/perf/util/c++/clang.cpp | 38 ++++++++++++++++++++++++++++++++++++++
 tools/perf/util/c++/clang.h   |  7 +++++++
 2 files changed, 45 insertions(+)

diff --git a/tools/perf/util/c++/clang.cpp b/tools/perf/util/c++/clang.cpp
index 042db68..8a0f818 100644
--- a/tools/perf/util/c++/clang.cpp
+++ b/tools/perf/util/c++/clang.cpp
@@ -112,15 +112,53 @@ getModuleFromSource(llvm::opt::ArgStringList CFlags, StringRef Path)
 
 PerfModule::PerfModule(std::unique_ptr<llvm::Module>&& M) : Module(std::move(M))
 {
+	for (llvm::Function& F : *Module) {
+		if (F.getLinkage() != llvm::GlobalValue::ExternalLinkage)
+			continue;
+
+		if (StringRef(F.getSection()).startswith("perfhook:"))
+			JITFunctions.insert(&F);
+		else
+			BPFFunctions.insert(&F);
+	}
 
+	for (auto V = Module->global_begin(); V != Module->global_end(); V++) {
+		llvm::GlobalVariable *GV = &*V;
+		if (StringRef(GV->getSection()) == llvm::StringRef("maps"))
+			Maps.insert(GV);
+	}
 }
 
+void PerfModule::prepareBPF(void)
+{
+	/*
+	 * setLinkage(AvailableExternallyLinkage) causes LLVM
+	 * blindly skip the function. They still exist in Module
+	 * so we can bring them back by resetting linkage to
+	 * ExternalLinkage.
+	 */
+	for (llvm::Function *F : JITFunctions)
+		F->setLinkage(llvm::GlobalValue::AvailableExternallyLinkage);
+	for (llvm::Function *F : BPFFunctions)
+		F->setLinkage(llvm::GlobalValue::ExternalLinkage);
+
+}
+
+void PerfModule::prepareJIT(void)
+{
+	for (llvm::Function *F : BPFFunctions)
+		F->setLinkage(llvm::GlobalValue::AvailableExternallyLinkage);
+	for (llvm::Function *F : JITFunctions)
+		F->setLinkage(llvm::GlobalValue::ExternalLinkage);
+
+}
 
 std::unique_ptr<llvm::SmallVectorImpl<char>>
 PerfModule::toBPFObject(void)
 {
 	using namespace llvm;
 
+	prepareBPF();
 	std::string TargetTriple("bpf-pc-linux");
 	std::string Error;
 	const Target* Target = TargetRegistry::lookupTarget(TargetTriple, Error);
diff --git a/tools/perf/util/c++/clang.h b/tools/perf/util/c++/clang.h
index cbb291b..1eb71a6 100644
--- a/tools/perf/util/c++/clang.h
+++ b/tools/perf/util/c++/clang.h
@@ -6,6 +6,7 @@
 #include "llvm/IR/Module.h"
 #include "llvm/Option/Option.h"
 #include <memory>
+#include <set>
 
 namespace perf {
 
@@ -14,6 +15,12 @@ using namespace llvm;
 class PerfModule {
 private:
 	std::unique_ptr<llvm::Module> Module;
+
+	std::set<llvm::GlobalVariable *> Maps;
+	std::set<llvm::Function *> BPFFunctions;
+	std::set<llvm::Function *> JITFunctions;
+	void prepareBPF(void);
+	void prepareJIT(void);
 public:
 	inline llvm::Module *getModule(void)
 	{
-- 
2.10.1