Re: [PATCH v3 19/30] perf clang jit: Insignt BPF and JIT functions in a Module

[Alexei Starovoitov]

On Sat, Nov 26, 2016 at 07:03:43AM +, Wang Nan wrote:
> 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 
...
> +void PerfModule::prepareBPF(void)
> +{
> + 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);
> +
> +}

Nice trick.
Please document it in the perf+llvm design doc.

Acked-by: Alexei Starovoitov 

[PATCH v3 19/30] 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 
Cc: Arnaldo Carvalho de Melo 
Cc: Alexei Starovoitov 
Cc: He Kuang 
Cc: Jiri Olsa 
Cc: Zefan Li 
Cc: pi3or...@163.com
---
 tools/perf/util/c++/clang.cpp | 32 
 tools/perf/util/c++/clang.h   |  7 +++
 2 files changed, 39 insertions(+)

diff --git a/tools/perf/util/c++/clang.cpp b/tools/perf/util/c++/clang.cpp
index d31b0a5..98d05e2 100644
--- a/tools/perf/util/c++/clang.cpp
+++ b/tools/perf/util/c++/clang.cpp
@@ -115,15 +115,47 @@ getModuleFromSource(llvm::opt::ArgStringList CFlags, 
StringRef Path)
 
 PerfModule::PerfModule(std::unique_ptr&& 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)
+{
+   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>
 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 
+#include 
 
 namespace perf {
 
@@ -14,6 +15,12 @@ using namespace llvm;
 class PerfModule {
 private:
std::unique_ptr Module;
+
+   std::set Maps;
+   std::set BPFFunctions;
+   std::set JITFunctions;
+   void prepareBPF(void);
+   void prepareJIT(void);
 public:
inline llvm::Module *getModule(void)
{
-- 
2.10.1