一般的Pass工程建立方法需要利用LLVM源码目录进行编译，本文介绍了另一种Pass工程建立和编译方法，与cmake相结合进行Pass编译。

1. 环境安装

  • 安装LLVM和clang编译器
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sudo apt-get install clang
sudo apt-get install clang++
sudo apt-get install llvm

2. LLVM Pass工程目录

该测试工程LLVM_Test主要包含两个文件夹cmake和src，其具体文件组织形式如下图所示。需要注意的是，利用该工程编译Pass时只需要在src目录下添加相应的Pass源码即可，其他文件不需要修改。

具体内容如下：

  • cmake目录中的FindLLVM.cmake
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# - Find LLVM 
# This module can be used to find LLVM.
# It requires that the llvm-config executable be available on the system path.
# Once found, llvm-config is used for everything else.
#
# The following variables are set:
#
# LLVM_FOUND                 - Set to YES if LLVM is found.
# LLVM_VERSION               - Set to the decimal version of the LLVM library.
# LLVM_INCLUDE_DIRS          - A list of directories where the LLVM headers are located.
# LLVM_LIBRARY_DIRS          - A list of directories where the LLVM libraries are located.
# LLVM_LIBRARIES             - A list of libraries which should be linked
# LLVM_DYNAMIC_LIBRARY       - A single dynamic llvm shared library
# LLVM_DYNAMIC_LIBRARY_FOUND - Whether found the dynamic llvm shared library
# LLVM_OPT                   - opt program in llvm
# 
# Using Following macros to set static library:
# llvm_map_components_to_libraries(OUTPUT_VARIABLE ${llvm components})
# 
# tutorial:
#   1.  select default LLVM version:
#       cmake .. -DLLVM_RECOMMEND_VERSION="3.5"
#   2.  set include dir and link dir:
#       include_directories(${LLVM_INCLUDE_DIRS})
#       link_directories(${LLVM_LIBRARY_DIRS})
#   3.a link static libraries:
#       llvm_map_components_to_libraries(LLVM_IRREADER_LIRARY irreader)
#       target_link_libraries(target
#           ${LLVM_LIBRARIES}
#           ${LLVM_IRREADER_LIRARY}
#           )
#   3.b link a dynamic library:
#       target_link_libraries(target ${LLVM_DYNAMIC_LIBRARY}) 
#
# 14-10-26: 
#    LLVM_RECOMMAND_VERSION --> LLVM_RECOMMEND_VERSION
#    update tutorial
# 
# version: 0.9.1
#    add LLVM_FLAGS_NDEBUG means llvm build with NDEBUG
#
# version: 0.9
#    remove LLVM_{C/CPP/CXX}_FLAGS which import -DNDEBUG
#
#
if(NOT DEFINED LLVM_RECOMMEND_VERSION)
   set(LLVM_RECOMMEND_VERSION "" CACHE STRING "Switch the llvm version")
   set_property(CACHE LLVM_RECOMMEND_VERSION PROPERTY STRINGS "" "3.4" "3.5" "3.9")
endif()


if(NOT(DEFINED LLVM_ROOT) )
	if(NOT "${LLVM_VERSION}" EQUAL "{LLVM_RECOMMEND_VERSION}")
		unset(LLVM_CONFIG_EXE CACHE)
		unset(LLVM_DYNAMIC_LIBRARY CACHE)
	endif()
	# find llvm-config. perfers to the one with version suffix, Ex:llvm-config-3.2
	find_program(LLVM_CONFIG_EXE NAMES "llvm-config-${LLVM_RECOMMEND_VERSION}" "llvm-config")
   find_program(LLVM_OPT NAMES "opt-${LLVM_RECOMMEND_VERSION}" "opt")

	if(NOT LLVM_CONFIG_EXE)
		set(LLVM_FOUND False)
      message(FATAL_ERROR "Not Found LLVM (LLVM_RECOMMEND_VERSION=${LLVM_RECOMMEND_VERSION})")
	else()
		set(LLVM_FOUND True)
	endif()

	# Get the directory of llvm by using llvm-config. also remove whitespaces.
	execute_process(COMMAND ${LLVM_CONFIG_EXE} --prefix OUTPUT_VARIABLE LLVM_ROOT
		OUTPUT_STRIP_TRAILING_WHITESPACE )

endif()

macro(_llvm_config _var_name)
    execute_process(COMMAND ${LLVM_CONFIG_EXE} ${ARGN} 
        OUTPUT_VARIABLE ${_var_name}
        OUTPUT_STRIP_TRAILING_WHITESPACE
        )
endmacro()

set(LLVM_INSTALL_PREFIX  ${LLVM_ROOT})
add_definitions(-D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS)

_llvm_config(LLVM_VERSION --version)
STRING(REGEX REPLACE "^([0-9]+)\\.[0-9]+(svn)?\\.?[0-9]*" "\\1" LLVM_VERSION_MAJOR "${LLVM_VERSION}")
STRING(REGEX REPLACE "^[0-9]+\\.([0-9]+)(svn)?\\.?[0-9]*" "\\1" LLVM_VERSION_MINOR "${LLVM_VERSION}")
_llvm_config(LLVM_LD_FLAGS --ldflags)
_llvm_config(LLVM_LIBRARY_DIRS --libdir)
_llvm_config(LLVM_INCLUDE_DIRS --includedir)
string(REGEX MATCH "-l.*" LLVM_LIBRARIES ${LLVM_LD_FLAGS})
_llvm_config(LLVM_C_FLAGS --cflags)
if(LLVM_C_FLAGS MATCHES "-DNDEBUG")
   add_definitions(-DLLVM_FLAGS_NDEBUG)
endif()

find_library(LLVM_DYNAMIC_LIBRARY 
	NAMES "LLVM" "LLVM-${LLVM_VERSION}"
   PATHS ${LLVM_LIBRARY_DIRS}
   )

if(NOT LLVM_DYNAMIC_LIBRARY)
	set(LLVM_DYNAMIC_LIBRARY_FOUND False)
else()
	set(LLVM_DYNAMIC_LIBRARY_FOUND True)
endif()

macro(llvm_map_components_to_libraries _var_name)
    _llvm_config(${_var_name} --libs "${ARGN}")
endmacro()

message(STATUS "Found LLVM Version ${LLVM_VERSION} ")
  • 主目录的CMakeLists.txt
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cmake_minimum_required(VERSION 2.8)
project(Test)

set(CMAKE_MODULE_PATH 
   ${CMAKE_MODULE_PATH}
   ${CMAKE_SOURCE_DIR}/cmake
   )

if(NOT CMAKE_BUILD_TYPE)
   set(CMAKE_BUILD_TYPE "Release")
endif()

find_package(LLVM)

add_subdirectory(src)
  • src目录中的CMakeLists.txt
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aux_source_directory(. DIR_SRCS)
include_directories(
	${LLVM_PROF_INCLUDE_DIRS}
	${PROJECT_BINARY_DIR}
	${LLVM_INCLUDE_DIRS} 
   ../include
	)
link_directories(
   ${LLVM_LIBRARY_DIRS} 
   )

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall --std=c++11 -fno-rtti")
set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -DNO_DEBUG")
set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG}")

add_library(Test SHARED
	${DIR_SRCS}
	)

target_link_libraries(Test
	${LLVM_DYNAMIC_LIBRARY}
	)
  • src中的FunctionTest.cpp文件是LLVM Pass的一个示例，在该目录中可以编写相应的Pass
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#include <llvm/Pass.h>
#include <llvm/IR/Function.h>
#include <llvm/IR/Module.h>
#include <llvm/IR/Instructions.h>
#include <llvm/IR/Constants.h>
#include <llvm/Support/raw_ostream.h>
#include <llvm/IR/InstIterator.h>
#include <llvm/IR/Operator.h>
#include <llvm/Analysis/AliasAnalysis.h>
using namespace llvm;
namespace{
    class MyTest:public FunctionPass
    {
        public:
            static char ID;
            MyTest():FunctionPass(ID){}
            bool runOnFunction(Function &F) override;
    };
}
char MyTest::ID = 0;
static RegisterPass<MyTest> X("MyTest","My Test",false,false);
bool MyTest::runOnFunction(Function &F) {

    Function *tmp = &F;
    errs()<<tmp->getName()<<"\n";
    // 遍历函数中的所有基本块
    for (Function::iterator bb = tmp->begin(); bb != tmp->end(); ++bb) {
        // 遍历基本块中的每条指令
        for (BasicBlock::iterator inst = bb->begin(); inst != bb->end(); ++inst) {
            if (inst->isBinaryOp()) {
			errs()<<*inst<<"\n";
            }
        }
    }

    return false;
}

3. 编译过程

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cd LLVM_Test/
mkdir build
cd build/
cmake ..
make

编译出来的.so文件在LLVM_Test/build/src目录下。具体过程如下图所示：

4. Pass调用

利用该工程编译之后，我们就可以调用相应的Pass了，具体调用过程如下：

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opt -load LLVM_Test/build/src/libTest.so -MyTest test.ll