0x01 配置

Clang是LLVM的编译前端，我们的OC、Swift通过Clang经过预处理、词语分析、语法分析，最后生成IR中间码后，交由LLVM进行优化，最后针对不同的平台将IR转换成对应平台的汇编代码。

本篇需要对Clang进行一些定制化，所以我们需要重新编译llvm，步骤如下：

下载源码
- cd 需要下载源码的目录
  
  git clone http://llvm.org/git/llvm.git
- cd llvm/tools
  
  git clone http://llvm.org/git/clang.git
- cd ../projects
  
  git clone http://llvm.org/git/compiler-rt.git
- cd ../tools/clang/tools
  
  git clone http://llvm.org/git/clang-tools-extra.git
编译
- 安装cmake
  
  brew install cmake
- 编译
  - mkdir 新建的目录名 (因为不支持源代码目录内编译)
  - cd 新建的目录名
  - cmake llvm源代码目录
  - cmake –build .

参考链接：http://llvm.org/docs/CMake.html，编译完所有的工具都在编译目录下的bin目录下。

0x02 试玩

我们有代码如下

#import <UIKit/UIKit.h>
#import "AppDelegate.h"
#import "Animal.h"

#define NUM_1  100
#define NUM_2  200


int main(int argc, char * argv[]) {
    int a = NUM_1 + NUM_2;
    return 0;
}

预处理

经过预处理后的代码会是什么样的？使用Clang命令如下

clang -E main.m

# 1 "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk/System/Library/Frameworks/Foundation.framework/Headers/FoundationLegacySwiftCompatibility.h" 1 3
# 185 "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk/System/Library/Frameworks/Foundation.framework/Headers/Foundation.h" 2 3
# 10 "./Animal.h" 2

int main(int argc, char * argv[]) {
    int a = 100 + 200;

    return 0;
}

预处理的过程中，导入了头文件，并把宏替换了。

词法分析

词法分析的命令

clang -fsyntax-only -Xclang -dump-tokens main.m

int 'int'	 [StartOfLine]	Loc=<main.m:17:1>
identifier 'main'	 [LeadingSpace]	Loc=<main.m:17:5>
l_paren '('		Loc=<main.m:17:9>
int 'int'		Loc=<main.m:17:10>
identifier 'argc'	 [LeadingSpace]	Loc=<main.m:17:14>
comma ','		Loc=<main.m:17:18>
char 'char'	 [LeadingSpace]	Loc=<main.m:17:20>
star '*'	 [LeadingSpace]	Loc=<main.m:17:25>
identifier 'argv'	 [LeadingSpace]	Loc=<main.m:17:27>
l_square '['		Loc=<main.m:17:31>
r_square ']'		Loc=<main.m:17:32>
r_paren ')'		Loc=<main.m:17:33>
l_brace '{'	 [LeadingSpace]	Loc=<main.m:17:35>
int 'int'	 [StartOfLine] [LeadingSpace]	Loc=<main.m:18:5>
identifier 'a'	 [LeadingSpace]	Loc=<main.m:18:9>
equal '='	 [LeadingSpace]	Loc=<main.m:18:11>
numeric_constant '100'	 [LeadingSpace]	Loc=<main.m:18:13 <Spelling=main.m:13:16>>
plus '+'	 [LeadingSpace]	Loc=<main.m:18:19>
numeric_constant '200'	 [LeadingSpace]	Loc=<main.m:18:21 <Spelling=main.m:14:16>>
semi ';'		Loc=<main.m:18:26>
int 'int'	 [StartOfLine] [LeadingSpace]	Loc=<main.m:19:5>
identifier 'b'	 [LeadingSpace]	Loc=<main.m:19:9>
equal '='	 [LeadingSpace]	Loc=<main.m:19:11>
numeric_constant '1'	 [LeadingSpace]	Loc=<main.m:19:13>
plus '+'	 [LeadingSpace]	Loc=<main.m:19:15>
numeric_constant '2'	 [LeadingSpace]	Loc=<main.m:19:17>
semi ';'		Loc=<main.m:19:18>
return 'return'	 [StartOfLine] [LeadingSpace]	Loc=<main.m:21:5>
numeric_constant '0'	 [LeadingSpace]	Loc=<main.m:21:12>
semi ';'		Loc=<main.m:21:13>
r_brace '}'	 [StartOfLine]	Loc=<main.m:25:1>
eof ''		Loc=<main.m:25:2>

语法分析

语法分析命令如下

clang -fsyntax-only -Xclang -ast-dump main.m

-FunctionDecl 0x7ff34f2eeae8 <main.m:17:1, line:25:1> line:17:5 main 'int (int, char **)'
  |-ParmVarDecl 0x7ff34f2ee918 <col:10, col:14> col:14 argc 'int'
  |-ParmVarDecl 0x7ff34f2ee9d0 <col:20, col:32> col:27 argv 'char **':'char **'
  `-CompoundStmt 0x7ff34f2eedb8 <col:35, line:25:1>
    |-DeclStmt 0x7ff34f2eec70 <line:18:5, col:26>
    | `-VarDecl 0x7ff34f2eeba8 <col:5, line:14:16> line:18:9 a 'int' cinit
    |   `-BinaryOperator 0x7ff34f2eec48 <line:13:16, line:14:16> 'int' '+'
    |     |-IntegerLiteral 0x7ff34f2eec08 <line:13:16> 'int' 100
    |     `-IntegerLiteral 0x7ff34f2eec28 <line:14:16> 'int' 200
    |-DeclStmt 0x7ff34f2eed68 <line:19:5, col:18>
    | `-VarDecl 0x7ff34f2eeca0 <col:5, col:17> col:9 b 'int' cinit
    |   `-BinaryOperator 0x7ff34f2eed40 <col:13, col:17> 'int' '+'
    |     |-IntegerLiteral 0x7ff34f2eed00 <col:13> 'int' 1
    |     `-IntegerLiteral 0x7ff34f2eed20 <col:17> 'int' 2
    `-ReturnStmt 0x7ff34f2eeda0 <line:21:5, col:12>
      `-IntegerLiteral 0x7ff34f2eed80 <col:12> 'int' 0

生成IR

IR是作为Clang的输出，llvm的输入，命令如下

clang -S -fobjc-arc -emit-llvm main.m -o main.ll

; ModuleID = 'main.m'
source_filename = "main.m"
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx10.13.0"

; Function Attrs: noinline nounwind optnone ssp uwtable
define i32 @main(i32, i8**) #0 {
  %3 = alloca i32, align 4
  %4 = alloca i32, align 4
  %5 = alloca i8**, align 8
  %6 = alloca i32, align 4
  %7 = alloca i32, align 4
  store i32 0, i32* %3, align 4
  store i32 %0, i32* %4, align 4
  store i8** %1, i8*** %5, align 8
  store i32 300, i32* %6, align 4
  store i32 3, i32* %7, align 4
  ret i32 0
}

attributes #0 = { noinline nounwind optnone ssp uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="penryn" "target-features"="+cx16,+fxsr,+mmx,+sse,+sse2,+sse3,+sse4.1,+ssse3,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }

!llvm.module.flags = !{!0, !1, !2, !3, !4, !5, !6}
!llvm.ident = !{!7}

!0 = !{i32 1, !"Objective-C Version", i32 2}
!1 = !{i32 1, !"Objective-C Image Info Version", i32 0}
!2 = !{i32 1, !"Objective-C Image Info Section", !"__DATA,__objc_imageinfo,regular,no_dead_strip"}
!3 = !{i32 4, !"Objective-C Garbage Collection", i32 0}
!4 = !{i32 1, !"Objective-C Class Properties", i32 64}
!5 = !{i32 1, !"wchar_size", i32 4}
!6 = !{i32 7, !"PIC Level", i32 2}
!7 = !{!"Apple LLVM version 9.1.0 (clang-902.0.39.2)"}

其他

生成字节码

clang -emit-llvm -c main.m -o main.bc
生成汇编

clang -S -fobjc-arc main.m -o main.s
生成目标文件

clang -fmodules -c main.m -o main.o
生成可执行文件

clang main.o -o main

0x03 第一个插件

初始化一个插件项目

打开源码路径llvm/tools/clang/example，example目录下新建目录，此例中为DemoPlugin。

接着，修改example目录的CMakeLists.txt文件，添加如下：

1	add_subdirectory(DemoPlugin)

来到testPlugin目录，新建如下三个文件

CMakeLists.txt
DemoPlugin.exports
DemoPlugin.cpp

其中CMakeLists.txt内容如下，可以参考example目录下其他例子的CMakeLists.txt内容。

# If we don't need RTTI or EH, there's no reason to export anything
# from the plugin.
if( NOT MSVC ) 
  if( NOT LLVM_REQUIRES_RTTI )
    if( NOT LLVM_REQUIRES_EH )
      set(LLVM_EXPORTED_SYMBOL_FILE ${CMAKE_CURRENT_SOURCE_DIR}/DemoPlugin.exports)
    endif()
  endif()
endif()

add_llvm_loadable_module(DemoPlugin DemoPlugin.cpp PLUGIN_TOOL clang)

if(LLVM_ENABLE_PLUGINS AND (WIN32 OR CYGWIN))
  target_link_libraries(DemoPlugin PRIVATE
    clangAST
    clangBasic
    clangFrontend
    LLVMSupport
    )
endif()

然后开始最重要的testPlugin.cpp代码编写，

#include "clang/Frontend/FrontendPluginRegistry.h"
#include "clang/AST/AST.h"
#include "clang/AST/ASTConsumer.h"
#include "clang/Frontend/CompilerInstance.h"

using namespace clang;

namespace
{
    class DemoPluginConsumer : public ASTConsumer
    {
    CompilerInstance &Instance;
    std::set<std::string> ParsedTemplates;
    public:
        DemoPluginConsumer(CompilerInstance &Instance,
                               std::set<std::string> ParsedTemplates)
        : Instance(Instance), ParsedTemplates(ParsedTemplates) {}
    };

    class DemoPluginASTAction : public PluginASTAction
    {
    std::set<std::string> ParsedTemplates;
    protected:
        std::unique_ptr<ASTConsumer> CreateASTConsumer(CompilerInstance &CI,
                                                       llvm::StringRef) override
        {
            return llvm::make_unique<DemoPluginConsumer>(CI, ParsedTemplates);
        }
		// 插件的入口函数
        bool ParseArgs(const CompilerInstance &CI,
                       const std::vector<std::string> &args) override {

            DiagnosticsEngine &D = CI.getDiagnostics();
            // Report的作用是向编译器报错
            D.Report(D.getCustomDiagID(DiagnosticsEngine::Error,
                                       "Hello Plugin"));

            return true;
        }
    };
}

static clang::FrontendPluginRegistry::Add<DemoPluginASTAction>
X("DemoPlugin", "demo plugin");

编译，在我们的之前编译源码时新建的目录

cmake
- cmake llvm源代码目录
- cmake –build .
- make DemoPlugin
- 插件出现在lib目录下，DemoPlugin.dylib
Xcode
- cmake -G Xcode .llvm源代码目录 -DCMAKE_BUILD_TYPE:STRING=MinSizeRel
- 打开LLVM.xcodeproj
- 选择Automatically Create Schemes
- 编译clang、DemoPlugin
- 插件出现在Debug/lib目录下，DemoPlugin.dylib

配置Xcode

Xcode的Build Setting里的Other C Flags添加如下，也就是DemoPlugin.dylib所在目录

-Xclang -load -Xclang /Users/ex-lifenglei/Desktop/llvm/myBuild/lib/DemoPlugin.dylib -Xclang -add-plugin -Xclang DemoPlugin

Build_Setting

这时，我们build下我们的项目大多数会遇到下面的报错

Build_Error

这是因为Xcode的Clang版本跟我们自己编译的Clang版本不一致。Clang插件需要对应的Clang版本来加载。所以我们还得修改Xcode指定的Clang。在Xcode的Build Setting里新增两个自定义项。

CC = /Users/ex-lifenglei/Desktop/llvm/myBuild/bin/clang-7

CXX = /Users/ex-lifenglei/Desktop/llvm/myBuild/bin/clang-7

Build_Setting

然而在Xcode 9版本上，继续报错了，如下

Build_Error

解决办法就是关掉Build Setting里的Index-While-Building

Build_Setting

紧接着再次编译，我们成功编译失败，那是当然的，我们本来就设置了一个编译错误提示，说明我们的插件成功运行了！！！

Build_Success

但是，因为这里是error，所以编译终止了，如果上面代码改成Warning让代码继续执行下去的话，可能会遇到下面这个错误

Build_Error

解决方法就是把Xcode程序下的libarclite_iphonesimulator拷贝到编译目录下的../lib/arc下。如果是真机，也是同样的方法把libarclite_iphoneos.a复制过来。

/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/arc/libarclite_iphonesimulator.a

我们再做个试验，我们把所有的类名和方法给打出来，代码如下

#include "clang/Frontend/FrontendPluginRegistry.h"
#include "clang/AST/AST.h"
#include "clang/AST/ASTConsumer.h"
#include "clang/AST/RecursiveASTVisitor.h"
#include "clang/Frontend/CompilerInstance.h"

using namespace clang;

namespace
{
    // 可以深度优先搜索整个AST，并访问每一个基类，遍历需要处理的节点
    class DemoPluginVisitor : public RecursiveASTVisitor<DemoPluginVisitor>
    {
    private:
        CompilerInstance &Instance;
        ASTContext *Context;
        
    public:
        void setASTContext (ASTContext &context)
        {
            this -> Context = &context;
        }
        
        DemoPluginVisitor (CompilerInstance &Instance)
        :Instance(Instance) {}
        
        // 查找类名
        bool VisitObjCInterfaceDecl(ObjCInterfaceDecl *declaration) {
            if(isUserSourceCode(declaration)) {
                DiagnosticsEngine &D = Instance.getDiagnostics();
                unsigned diagID = D.getCustomDiagID(DiagnosticsEngine::Warning, "查找到一个类名: %0");
                D.Report(declaration->getLocStart(), diagID) << declaration->getName();
            }
            return true;
        }
        
        // 查找方法名
        bool VisitObjCMethodDecl(ObjCMethodDecl *declaration) {
            if(isUserSourceCode(declaration)) {
                DiagnosticsEngine &D = Instance.getDiagnostics();
                unsigned diagID = D.getCustomDiagID(DiagnosticsEngine::Warning, "查找到一个方法名: %0");
//                D.Report(declaration->getLocStart(), diagID).AddString(declaration->getSelector().getAsString());
                 D.Report(declaration->getLocStart(), diagID) << declaration->getSelector().getAsString();
            }
            return true;
        }
        
        // 是否用户代码
        bool isUserSourceCode (Decl *decl){
            std::string filename = Instance.getSourceManager().getFilename(decl->getSourceRange().getBegin()).str();
            
            if (filename.empty())
                return false;
            // 定义非Xcode中的源码都是用户源码
            if(filename.find("/Applications/Xcode.app/") == 0)
                return false;
            
            return true;
        }
    };
    
    class DemoPluginConsumer : public ASTConsumer
    {
    private:
        DemoPluginVisitor visitor;
        CompilerInstance &Instance;
        std::set<std::string> ParsedTemplates;
    public:
        DemoPluginConsumer(CompilerInstance &Instance,
                           std::set<std::string> ParsedTemplates)
        : Instance(Instance), ParsedTemplates(ParsedTemplates), visitor(Instance) {}
        
        // 每次分析到一个顶层定义时会回调此函数，返回true表示处理
        bool HandleTopLevelDecl(DeclGroupRef DG) override
        {
            return true;
        }
        
        // ASTConsumer的入口函数
        void HandleTranslationUnit(ASTContext& context) override
        {
            visitor.setASTContext(context);
            visitor.TraverseDecl(context.getTranslationUnitDecl());
        }
    };
    
    class DemoPluginASTAction : public PluginASTAction
    {
        std::set<std::string> ParsedTemplates;
    protected:
        std::unique_ptr<ASTConsumer> CreateASTConsumer(CompilerInstance &CI,
                                                       llvm::StringRef) override
        {
            return llvm::make_unique<DemoPluginConsumer>(CI, ParsedTemplates);
        }
        // 插件的入口函数
        bool ParseArgs(const CompilerInstance &CI,
                       const std::vector<std::string> &args) override {
            return true;
        }
    };
}

static clang::FrontendPluginRegistry::Add<DemoPluginASTAction>
X("DemoPlugin", "demo plugin");

运行结果如下，我们所有的类名和方法名都被打出来了。

Build_Demo