LLVM hello world pass

Question

I just start learning LLVM and follow the start-up website quick-start-writing-hello-world to write my first HelloPass.

However, it doesn't work as expected.

The llvm version is 16.0.6

Here are my steps.

The cmakelist is a bit different from the doc, because I don't include my project into the LLVM source. And I follow Developing LLVM passes out of source.

The project structure: . ├── CMakeLists.txt ├── helloPass │ ├── CMakeLists.txt │ └── hello.cpp

In CMakeLists.txt:

cmake_minimum_required(VERSION 3.25)
project(llvm_kernel CXX C)

set(CMAKE_CXX_STANDARD 17)
set(LLVM_PATH /usr/lib/llvm-16)
set(CMAKE_C_COMPILER /usr/bin/clang)
set(CMAKE_CXX_COMPILER /usr/bin/clang++)

find_package(LLVM REQUIRED CONFIG)

separate_arguments(LLVM_DEFINITIONS_LIST NATIVE_COMMAND ${LLVM_DEFINITIONS})
add_definitions(${LLVM_DEFINITIONS_LIST})

include_directories(${LLVM_PATH}/include)

add_subdirectory(helloPass)

In helloPass/CMakeLists.txt:

cmake_minimum_required(VERSION 3.25)

add_library(HelloPass MODULE hello.cpp)

set_target_properties(HelloPass PROPERTIES
        COMPILE_FLAGS "-fno-rtti"
)

In helloPass/hello.cpp

#include "llvm/Pass.h"
#include "llvm/IR/Function.h"
#include "llvm/Support/raw_ostream.h"

#include "llvm/IR/LegacyPassManager.h"

using namespace llvm;

namespace {
    struct Hello : public FunctionPass {
        static char ID;

        Hello() : FunctionPass(ID) {}

        bool runOnFunction(Function &F) override {
            errs() << "Hello: ";
            errs().write_escaped(F.getName()) << '\n';
            return false;
        }
    }; // end of struct Hello
}  // end of anonymous namespace

char Hello::ID = 0;
static RegisterPass<Hello> X("hello", "Hello World Pass",
                             false /* Only looks at CFG */,
                             false /* Analysis Pass */);

And the following is just to build the project like :

mkdir build && cd build
cmake ..
make

Now the libHelloPass.so is generated. It works fine till here. But it fails in the invocation.

I try to use opt to load the helloPass as the documentation Running a pass with opt¶ said but it fails with "opt: unknown pass name 'hello'". The opt command is like: opt -load build/helloPass/libHelloPass.so -p hello test.bc > /dev/null. I do a bit modification here followed the doc Invoking opt.

I also tried just list all passes but not found a pass called "hello" but only a "helloworld", which is not defined by me. opt -load build/helloPass/libHelloPass.so --print-passes | grep hello

Anyone can help me about this?

I have checked the paths of llvm-related tools like opt, clang, clang++, which are all located at /usr/lib/llvm-16/bin