Software tracer llvm pass

[Pavel-Durov]

Current issue

I added my Rust function in ykcapi/src/lib.rs (just cause I know that __ykrt_control_point function can be found there from ControlPoint.cpp module pass):

#[no_mangle]
pub extern "C" fn yk_trace_basic_block() -> *const c_void {
    println!("yk_trace_basic_block was called");
    std::ptr::null()
}

In my pass implementation, I'm locating and injecting external function call instruction to the basicblock.
My runOnModule function:

bool runOnModule(Module &M) override {
    for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
      LLVMContext &Context = M.getContext();
      if (externalFunc == NULL) {
        // Locate externally linked function
        FunctionType *FType = FunctionType::get(Type::getVoidTy(Context), {}, false);
        externalFunc = Function::Create(FType, GlobalVariable::ExternalLinkage,
                                        "yk_trace_basic_block", M);
      }
      for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
        for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE; ++BI) {
          // Insert function call instruction
          IRBuilder<> builder(Context);
          builder.SetInsertPoint(&(*BI));
          builder.CreateCall(externalFunc);
        }
      }
    }
    return true;
  }

But when I run it I get an undefined reference error from the linker:

 note: /usr/bin/ld: /yk-fork/target/debug/build/hwtracer-36df6aaa5f152db3/out/libhwtracer_c.a(collect.o): in function `hwt_set_cerr':
          /yk-fork/hwtracer/src/perf/collect.c:172: undefined reference to `yk_trace_basic_block'
          /usr/bin/ld: /yk-fork/hwtracer/src/perf/collect.c:172: undefined reference to `yk_trace_basic_block'
....
collect2: error: ld returned 1 exit status

And when I look at libykcapi.so symbols, I do see my function there:

nm -g -C ./target/debug/deps/libykcapi.so | grep yk_trace_basic_block
0000000000061050 T yk_trace_basic_block