浅谈编译过程

WYW:GCC wangyongwangyongwang$ GCC -ccc-print-phases main.c0: input, "main.c", c1: preprocessor, {0}, cpp-output2: compiler, {1}, ir3: backend, {2}, assembler4: assembler, {3}, object5: linker, {4}, image6: bind-arch, "x86_64", {5}, image

// 1: preprocessor 预编译WYW:GCCProcess wangyongwangyongwang$ gcc -E main.c -o main.i// 2: compiler生成汇编文件WYW:GCCProcess wangyongwangyongwang$ gcc -S main.i -o main.s// 3: backend、4: assembler生成目标文件WYW:GCCProcess wangyongwangyongwang$ gcc -c main.s -o main.o// 5: linker、6: bind-arch生成可执行文件WYW:GCCProcess wangyongwangyongwang$ gcc main.o -o main// 执行可执行文件WYW:GCCProcess wangyongwangyongwang$ sudo ./mainHello, World!

WYW:~ wangyongwangyongwang$ objdump --versionApple LLVM version 11.0.0 (clang-1100.0.33.17)  Optimized build.  Default target: x86_64-apple-darwin19.2.0  Host CPU: broadwell
  Registered Targets:    aarch64    - AArch64 (little endian)    aarch64_be - AArch64 (big endian)    arm        - ARM    arm64      - ARM64 (little endian)    armeb      - ARM (big endian)    thumb      - Thumb    thumbeb    - Thumb (big endian)    x86        - 32-bit X86: Pentium-Pro and above    x86-64     - 64-bit X86: EM64T and AMD64

WYW:LLVM wangyongwangyongwang$ clang -ccc-print-phases clang_main.c0: input, "clang_main.c", c1: preprocessor, {0}, cpp-output2: compiler, {1}, ir3: backend, {2}, assembler4: assembler, {3}, object5: linker, {4}, image6: bind-arch, "x86_64", {5}, image

// 一、预编译// 引入头文件预编译  注释的内容不会显示在预编译后的文件中#import <Foundation/Foundation.h>#import <Foundation/NSObjCRuntime.h>
// 条件编译#if __has_include(<UIKit/UIKit.h>)        #import <UIKit/UIKit.h>    #ifndef Qi_HAS_IMPORT_UIKit        #define QUC_HAS_IMPORT_UIKit 1    #endif#else    #ifndef Qi_HAS_IMPORT_UIKit        #define Qi_HAS_IMPORT_UIKit 0    #endif#endif
// 宏预编译#define QiShareAge 2// 带参数的宏预编译#define QiShareMember(Member, Name) Member#Name
int main(int argc, char * argv[]) {
    // NSString * appDelegateClassName;     @autoreleasepool {
         NSLog(@"Hello Clang Compile");
         const char *me = QiShareMember("QiShare","WYW");         printf("member：%s \n", me);         NSString *member = [NSString stringWithCString:me encoding:NSUTF8StringEncoding];         NSLog(@"member：%@", member);         // Setup code that might create autoreleased objects goes here.         // appDelegateClassName = NSStringFromClass([AppDelegate class]);         /** 输出内容          * Hello Clang Compile          * member：QiShare"WYW"          * member：QiShare"WYW"          */     }    // return UIApplicationMain(argc, argv, nil, appDelegateClassName);}

// 预编译命令clang -E main.m -o main_precompile.i

1. #include #import 预编译指令，将被包含的文件插入到该预编译指令的位置2. 删除所有的注释// 及 块注释 但是会保留注释所在行为空白行3. 添加行号和文件标识4. 因为编译器有需要，会保留#pragma 编译指令

# 1 "main.m"# 1 "<built-in>" 1# 1 "<built-in>" 3# 374 "<built-in>" 3# 1 "<command line>" 1# 1 "<built-in>" 2# 1 "main.m" 2# 11 "main.m"# 1 "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks/Foundation.framework/Headers/Foundation.h" 1 3
typedef enum __attribute__((enum_extensibility(closed))) NSComparisonResult : NSInteger NSComparisonResult; enum NSComparisonResult : NSInteger {    NSOrderedAscending = -1L,    NSOrderedSame,    NSOrderedDescending};

typedef NSComparisonResult (^NSComparator)(id obj1, id obj2);

typedef enum __attribute__((flag_enum,enum_extensibility(open))) NSEnumerationOptions : NSUInteger NSEnumerationOptions; enum NSEnumerationOptions : NSUInteger {    NSEnumerationConcurrent = (1UL << 0),    NSEnumerationReverse = (1UL << 1),};
# 1 "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks/Foundation.framework/Headers/FoundationLegacySwiftCompatibility.h" 1 3# 193 "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks/Foundation.framework/Headers/Foundation.h" 2 3# 12 "main.m" 2# 31 "main.m"int main(int argc, char * argv[]) {

     @autoreleasepool {
         NSLog(@"Hello Clang Compile");
         const char *me = "QiShare""\"WYW\"";         printf("member：%s \n", me);         NSString *member = [NSString stringWithCString:me encoding:NSUTF8StringEncoding];         NSLog(@"member：%@", member);     }
}

// 词法分析结果annot_module_include '#import <Foundation/Foundation.h>#import <Foundation/NSObjCRuntime.h>
// 条件编译#if __has_include(<UIKit/UIKit.h>)        #import <UIKit/UIKit.h>    #ifndef Qi_HAS_IMPORT_UIKit        #define QUC_HAS_IMPORT_UIKit 1    #endif#else  '        Loc=<main.m:11:1>annot_module_include '#import <Foundation/NSObjCRuntime.h>
// 条件编译#if __has_include(<UIKit/UIKit.h>)        #import <UIKit/UIKit.h>    #ifndef Qi_HAS_IMPORT_UIKit        #define QUC_HAS_IMPORT_UIKit 1    #endif#else    #ifndef Qi_HAS_IMPORT_UIKit        #define Qi_HAS_IMPORT_UIKit 0'        Loc=<main.m:12:1>int 'int'     [StartOfLine]    Loc=<main.m:31:1>identifier 'main'     [LeadingSpace]    Loc=<main.m:31:5>l_paren '('        Loc=<main.m:31:9>int 'int'        Loc=<main.m:31:10>identifier 'argc'     [LeadingSpace]    Loc=<main.m:31:14>comma ','        Loc=<main.m:31:18>char 'char'     [LeadingSpace]    Loc=<main.m:31:20>star '*'     [LeadingSpace]    Loc=<main.m:31:25>identifier 'argv'     [LeadingSpace]    Loc=<main.m:31:27>l_square '['        Loc=<main.m:31:31>r_square ']'        Loc=<main.m:31:32>r_paren ')'        Loc=<main.m:31:33>l_brace '{'     [LeadingSpace]    Loc=<main.m:31:35>at '@'     [StartOfLine] [LeadingSpace]    Loc=<main.m:34:6>identifier 'autoreleasepool'        Loc=<main.m:34:7>l_brace '{'     [LeadingSpace]    Loc=<main.m:34:23>identifier 'NSLog'     [StartOfLine] [LeadingSpace]    Loc=<main.m:36:10>l_paren '('        Loc=<main.m:36:15>at '@'        Loc=<main.m:36:16>string_literal '"Hello Clang Compile"'        Loc=<main.m:36:17>r_paren ')'        Loc=<main.m:36:38>semi ';'        Loc=<main.m:36:39>const 'const'     [StartOfLine] [LeadingSpace]    Loc=<main.m:38:10>char 'char'     [LeadingSpace]    Loc=<main.m:38:16>star '*'     [LeadingSpace]    Loc=<main.m:38:21>identifier 'me'        Loc=<main.m:38:22>equal '='     [LeadingSpace]    Loc=<main.m:38:25>string_literal '"QiShare"'     [LeadingSpace]    Loc=<main.m:38:27 <Spelling=main.m:38:41>>string_literal '"\"WYW\""'        Loc=<main.m:38:27 <Spelling=<scratch space>:3:1>>semi ';'        Loc=<main.m:38:57>identifier 'printf'     [StartOfLine] [LeadingSpace]    Loc=<main.m:39:10>l_paren '('        Loc=<main.m:39:16>string_literal '"member：%s \n"'        Loc=<main.m:39:17>comma ','        Loc=<main.m:39:33>identifier 'me'     [LeadingSpace]    Loc=<main.m:39:35>r_paren ')'        Loc=<main.m:39:37>semi ';'        Loc=<main.m:39:38>identifier 'NSString'     [StartOfLine] [LeadingSpace]    Loc=<main.m:40:10>star '*'     [LeadingSpace]    Loc=<main.m:40:19>identifier 'member'        Loc=<main.m:40:20>equal '='     [LeadingSpace]    Loc=<main.m:40:27>l_square '['     [LeadingSpace]    Loc=<main.m:40:29>identifier 'NSString'        Loc=<main.m:40:30>identifier 'stringWithCString'     [LeadingSpace]    Loc=<main.m:40:39>colon ':'        Loc=<main.m:40:56>identifier 'me'        Loc=<main.m:40:57>identifier 'encoding'     [LeadingSpace]    Loc=<main.m:40:60>colon ':'        Loc=<main.m:40:68>identifier 'NSUTF8StringEncoding'        Loc=<main.m:40:69>r_square ']'        Loc=<main.m:40:89>semi ';'        Loc=<main.m:40:90>identifier 'NSLog'     [StartOfLine] [LeadingSpace]    Loc=<main.m:41:10>l_paren '('        Loc=<main.m:41:15>at '@'        Loc=<main.m:41:16>string_literal '"member：%@"'        Loc=<main.m:41:17>comma ','        Loc=<main.m:41:30>identifier 'member'     [LeadingSpace]    Loc=<main.m:41:32>r_paren ')'        Loc=<main.m:41:38>semi ';'        Loc=<main.m:41:39>r_brace '}'     [StartOfLine] [LeadingSpace]    Loc=<main.m:49:6>r_brace '}'     [StartOfLine]    Loc=<main.m:51:1>eof ''        Loc=<main.m:51:2>

// WYW:clang wangyongwangyongwang$ clang -fmodules -fsyntax-only -Xclang -ast-dump main.m// 语法分析输出内容TranslationUnitDecl 0x7fbeb702da08 <<invalid sloc>> <invalid sloc>|-TypedefDecl 0x7fbeb702e2a0 <<invalid sloc>> <invalid sloc> implicit __int128_t '__int128'| `-BuiltinType 0x7fbeb702dfa0 '__int128'|-TypedefDecl 0x7fbeb702e308 <<invalid sloc>> <invalid sloc> implicit __uint128_t 'unsigned __int128'| `-BuiltinType 0x7fbeb702dfc0 'unsigned __int128'|-TypedefDecl 0x7fbeb702e3a0 <<invalid sloc>> <invalid sloc> implicit SEL 'SEL *'| `-PointerType 0x7fbeb702e360 'SEL *' imported|   `-BuiltinType 0x7fbeb702e200 'SEL'|-TypedefDecl 0x7fbeb702e478 <<invalid sloc>> <invalid sloc> implicit id 'id'| `-ObjCObjectPointerType 0x7fbeb702e420 'id' imported|   `-ObjCObjectType 0x7fbeb702e3f0 'id' imported|-TypedefDecl 0x7fbeb702e558 <<invalid sloc>> <invalid sloc> implicit Class 'Class'| `-ObjCObjectPointerType 0x7fbeb702e500 'Class' imported|   `-ObjCObjectType 0x7fbeb702e4d0 'Class' imported|-ObjCInterfaceDecl 0x7fbeb702e5a8 <<invalid sloc>> <invalid sloc> implicit Protocol|-TypedefDecl 0x7fbeb702e8e8 <<invalid sloc>> <invalid sloc> implicit __NSConstantString 'struct __NSConstantString_tag'| `-RecordType 0x7fbeb702e700 'struct __NSConstantString_tag'|   `-Record 0x7fbeb702e670 '__NSConstantString_tag'|-TypedefDecl 0x7fbeb702e980 <<invalid sloc>> <invalid sloc> implicit __builtin_ms_va_list 'char *'| `-PointerType 0x7fbeb702e940 'char *'|   `-BuiltinType 0x7fbeb702daa0 'char'|-TypedefDecl 0x7fbeb7834868 <<invalid sloc>> <invalid sloc> implicit __builtin_va_list 'struct __va_list_tag [1]'| `-ConstantArrayType 0x7fbeb7834810 'struct __va_list_tag [1]' 1|   `-RecordType 0x7fbeb7834690 'struct __va_list_tag'|     `-Record 0x7fbeb7834600 '__va_list_tag'|-ImportDecl 0x7fbeb79ef2a8 <main.m:11:1> col:1 implicit Foundation|-ImportDecl 0x7fbeb79ef2e0 <line:12:1> col:1 implicit Foundation.NSObjCRuntime|-FunctionDecl 0x7fbeb79ef580 <line:31:1, line:51:1> line:31:5 main 'int (int, char **)'| |-ParmVarDecl 0x7fbeb79ef330 <col:10, col:14> col:14 argc 'int'| |-ParmVarDecl 0x7fbeb79ef440 <col:20, col:32> col:27 argv 'char **':'char **'| `-CompoundStmt 0x7fbeb88158a8 <col:35, line:51:1>|   `-ObjCAutoreleasePoolStmt 0x7fbeb8815890 <line:34:6, line:49:6>|     `-CompoundStmt 0x7fbeb8815858 <line:34:23, line:49:6>|       |-CallExpr 0x7fbeb7a000d0 <line:36:10, col:38> 'void'|       | |-ImplicitCastExpr 0x7fbeb7a000b8 <col:10> 'void (*)(id, ...)' <FunctionToPointerDecay>|       | | `-DeclRefExpr 0x7fbeb79fffa8 <col:10> 'void (id, ...)' Function 0x7fbeb79ef688 'NSLog' 'void (id, ...)'|       | `-ImplicitCastExpr 0x7fbeb7a000f8 <col:16, col:17> 'id':'id' <BitCast>|       |   `-ObjCStringLiteral 0x7fbeb7a00038 <col:16, col:17> 'NSString *'|       |     `-StringLiteral 0x7fbeb7a00008 <col:17> 'char [20]' lvalue "Hello Clang Compile"|       |-DeclStmt 0x7fbeb7a005d0 <line:38:10, col:57>|       | `-VarDecl 0x7fbeb7a00128 <col:10, <scratch space>:3:1> main.m:38:22 used me 'const char *' cinit|       |   `-ImplicitCastExpr 0x7fbeb7a00208 <col:41, <scratch space>:3:1> 'const char *' <NoOp>|       |     `-ImplicitCastExpr 0x7fbeb7a001f0 <main.m:38:41, <scratch space>:3:1> 'char *' <ArrayToPointerDecay>|       |       `-StringLiteral 0x7fbeb7a001c8 <main.m:38:41, <scratch space>:3:1> 'char [13]' lvalue "QiShare\"WYW\""|       |-CallExpr 0x7fbeb7a006f0 <main.m:39:10, col:37> 'int'|       | |-ImplicitCastExpr 0x7fbeb7a006d8 <col:10> 'int (*)(const char *, ...)' <FunctionToPointerDecay>|       | | `-DeclRefExpr 0x7fbeb7a005e8 <col:10> 'int (const char *, ...)' Function 0x7fbeb7a00228 'printf' 'int (const char *, ...)'|       | |-ImplicitCastExpr 0x7fbeb7a00738 <col:17> 'const char *' <NoOp>|       | | `-ImplicitCastExpr 0x7fbeb7a00720 <col:17> 'char *' <ArrayToPointerDecay>|       | |   `-StringLiteral 0x7fbeb7a00648 <col:17> 'char [14]' lvalue "member\357\274\232%s \n"|       | `-ImplicitCastExpr 0x7fbeb7a00750 <col:35> 'const char *' <LValueToRValue>|       |   `-DeclRefExpr 0x7fbeb7a00670 <col:35> 'const char *' lvalue Var 0x7fbeb7a00128 'me' 'const char *'|       |-DeclStmt 0x7fbeb88156c8 <line:40:10, col:90>|       | `-VarDecl 0x7fbeb7a00780 <col:10, col:89> col:20 used member 'NSString *' cinit|       |   `-ObjCMessageExpr 0x7fbeb8815688 <col:29, col:89> 'NSString * _Nullable':'NSString *' selector=stringWithCString:encoding: class='NSString'|       |     |-ImplicitCastExpr 0x7fbeb8815670 <col:57> 'const char *' <LValueToRValue>|       |     | `-DeclRefExpr 0x7fbeb8815000 <col:57> 'const char *' lvalue Var 0x7fbeb7a00128 'me' 'const char *'|       |     `-DeclRefExpr 0x7fbeb8815330 <col:69> 'NSStringEncoding':'unsigned long' EnumConstant 0x7fbeb8815028 'NSUTF8StringEncoding' 'NSStringEncoding':'unsigned long'|       `-CallExpr 0x7fbeb88157d0 <line:41:10, col:38> 'void'|         |-ImplicitCastExpr 0x7fbeb88157b8 <col:10> 'void (*)(id, ...)' <FunctionToPointerDecay>|         | `-DeclRefExpr 0x7fbeb88156e0 <col:10> 'void (id, ...)' Function 0x7fbeb79ef688 'NSLog' 'void (id, ...)'|         |-ImplicitCastExpr 0x7fbeb8815800 <col:16, col:17> 'id':'id' <BitCast>|         | `-ObjCStringLiteral 0x7fbeb8815760 <col:16, col:17> 'NSString *'|         |   `-StringLiteral 0x7fbeb8815738 <col:17> 'char [12]' lvalue "member\357\274\232%@"|         `-ImplicitCastExpr 0x7fbeb8815818 <col:32> 'NSString *' <LValueToRValue>|           `-DeclRefExpr 0x7fbeb8815780 <col:32> 'NSString *' lvalue Var 0x7fbeb7a00780 'member' 'NSString *'`-<undeserialized declarations>

int int main(int argc, char * argv[]) {
}

'		Loc=<main.m:12:1>int 'int'	 [StartOfLine]	Loc=<main.m:31:1>int 'int'	 [LeadingSpace]	Loc=<main.m:31:5>identifier 'main'	 [LeadingSpace]	Loc=<main.m:31:9>l_paren '('		Loc=<main.m:31:13>

main.m:31:5: error: cannot combine with previous 'int' declaration specifierint int main(int argc, char * argv[]) {    ^TranslationUnitDecl 0x7ff14302c808 <<invalid sloc>> <invalid sloc>
...
|           `-DeclRefExpr 0x7ff143922b80 <col:32> 'NSString *' lvalue Var 0x7ff14391f780 'member' 'NSString *'`-<undeserialized declarations>1 error generated.

void logSomething(NSString *str1, NSString *str2) {
    NSLog(@"str1：%@--str2：%@", str1, str2);}
int main(int argc, char * argv[]) {
    // NSString * appDelegateClassName;     @autoreleasepool {     	logSomething(1, 2);     }}

main.m:41:23: warning: incompatible integer to pointer conversion passing 'int'      to parameter of type 'NSString *' [-Wint-conversion]         logSomething(1, 2);                      ^main.m:31:29: note: passing argument to parameter 'str1' herevoid logSomething(NSString *str1, NSString *str2) {                            ^main.m:41:26: warning: incompatible integer to pointer conversion passing 'int'      to parameter of type 'NSString *' [-Wint-conversion]         logSomething(1, 2);                         ^main.m:31:45: note: passing argument to parameter 'str2' herevoid logSomething(NSString *str1, NSString *str2) {                                            ^

WYW:clang wangyongwangyongwang$ clang -S -fobjc-arc -emit-llvm main.m -o main.llWYW:clang wangyongwangyongwang$ cat 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-macosx10.15.0"
// 常量字符串，缓存、实例变量、消息列表、属性列表等信息%0 = type opaque%struct.__NSConstantString_tag = type { i32*, i32, i8*, i64 }%struct._class_t = type { %struct._class_t*, %struct._class_t*, %struct._objc_cache*, i8* (i8*, i8*)**, %struct._class_ro_t* }%struct._objc_cache = type opaque%struct._class_ro_t = type { i32, i32, i32, i8*, i8*, %struct.__method_list_t*, %struct._objc_protocol_list*, %struct._ivar_list_t*, i8*, %struct._prop_list_t* }%struct.__method_list_t = type { i32, i32, [0 x %struct._objc_method] }%struct._objc_method = type { i8*, i8*, i8* }%struct._objc_protocol_list = type { i64, [0 x %struct._protocol_t*] }%struct._protocol_t = type { i8*, i8*, %struct._objc_protocol_list*, %struct.__method_list_t*, %struct.__method_list_t*, %struct.__method_list_t*, %struct.__method_list_t*, %struct._prop_list_t*, i32, i32, i8**, i8*, %struct._prop_list_t* }%struct._ivar_list_t = type { i32, i32, [0 x %struct._ivar_t] }%struct._ivar_t = type { i64*, i8*, i8*, i32, i32 }%struct._prop_list_t = type { i32, i32, [0 x %struct._prop_t] }%struct._prop_t = type { i8*, i8* }

@__CFConstantStringClassReference = external global [0 x i32]@.str = private unnamed_addr constant [20 x i8] c"Hello Clang Compile\00", section "__TEXT,__cstring,cstring_literals", align 1@_unnamed_cfstring_ = private global %struct.__NSConstantString_tag { i32* getelementptr inbounds ([0 x i32], [0 x i32]* @__CFConstantStringClassReference, i32 0, i32 0), i32 1992, i8* getelementptr inbounds ([20 x i8], [20 x i8]* @.str, i32 0, i32 0), i64 19 }, section "__DATA,__cfstring", align 8@.str.1 = private unnamed_addr constant [13 x i8] c"QiShare\22WYW\22\00", align 1@.str.2 = private unnamed_addr constant [14 x i8] c"member\EF\BC\9A%s \0A\00", align 1
; Function Attrs: nounwinddeclare i8* @llvm.objc.autoreleasePoolPush() #1
declare void @NSLog(i8*, ...) #2
declare i32 @printf(i8*, ...) #2
; Function Attrs: nonlazybinddeclare i8* @objc_msgSend(i8*, i8*, ...) #3
; Function Attrs: nounwinddeclare i8* @llvm.objc.retainAutoreleasedReturnValue(i8*) #1
; Function Attrs: nounwinddeclare void @llvm.objc.storeStrong(i8**, i8*) #1
; Function Attrs: nounwinddeclare void @llvm.objc.autoreleasePoolPop(i8*) #1
!0 = !{i32 2, !"SDK Version", [2 x i32] [i32 10, i32 15]}!1 = !{i32 1, !"Objective-C Version", i32 2}!2 = !{i32 1, !"Objective-C Image Info Version", i32 0}!3 = !{i32 1, !"Objective-C Image Info Section", !"__DATA,__objc_imageinfo,regular,no_dead_strip"}!4 = !{i32 4, !"Objective-C Garbage Collection", i32 0}!5 = !{i32 1, !"Objective-C Class Properties", i32 64}!6 = !{i32 1, !"wchar_size", i32 4}!7 = !{i32 7, !"PIC Level", i32 2}!8 = !{!"Apple clang version 11.0.0 (clang-1100.0.33.17)"}!9 = !{}

// WYW:clang wangyongwangyongwang$ clang -S main.m -o main_compile.s// WYW:clang wangyongwangyongwang$ cat main_compile.s

// 汇编指令// .section 指令指定接下来会执行哪一个段。    .section	__TEXT,__text,regular,pure_instructions	.build_version macos, 10, 15	sdk_version 10, 15// .globl 指令说明 _main 是一个外部符号。这就是我们的 main() 函数。这个函数对于二进制文件外部来说是可见的，因为系统要调用它来运行可执行文件。	.globl	_main                   ## -- Begin function main// .align 指令指出了后面代码的对齐方式。在我们的代码中，后面的代码会按照 16(2^4) 字节对齐，如果需要的话，用 0x90 补齐。	.p2align	4, 0x90

// main 函数的头部：_main:                                  ## @main
// .cfi_startproc 指令通常用于函数的开始处。CFI 是调用帧信息 (Call Frame Information) 的缩写。这个调用 帧 以松散的方式对应着一个函数。它与后面的 .cfi_endproc 相匹配，以此标记出 main() 函数结束的地方。    .cfi_startproc
## %bb.0:// 在 OS X上，我们会有 X86_64 的代码，对于这种架构，有一个东西叫做 ABI ( 应用二进制接口 application binary interface)，ABI 指定了函数调用是如何在汇编代码层面上工作的。在函数调用期间，ABI 会让 rbp 寄存器 (基础指针寄存器 base pointer register) 被保护起来。当函数调用返回时，确保 rbp 寄存器的值跟之前一样，这是属于 main 函数的职责。pushq %rbp 将 rbp 的值 push 到栈中，以便我们以后将其 pop 出来。	pushq	%rbp
// 接下来是两个 CFI 指令：这将会输出一些关于生成调用堆栈展开和调试的信息。我们改变了堆栈和基础指针，而这两个指令可以告诉编译器它们都在哪儿，或者更确切的，它们可以确保之后调试器要使用这些信息时，能找到对应的东西。	.cfi_def_cfa_offset 16	.cfi_offset %rbp, -16// 接下来，movq %rsp, %rbp 将把局部变量放置到栈上。subq $32, %rsp 将栈指针移动 32 个字节，也就是函数会调用的位置。我们先将老的栈指针存储到 rbp 中，然后将此作为我们局部变量的基址，接着我们更新堆栈指针到我们将会使用的位置。	movq	%rsp, %rbp	.cfi_def_cfa_register %rbp	subq	$64, %rsp	movl	%edi, -4(%rbp)	movq	%rsi, -16(%rbp)// 调用 autoreleasePoolPush	callq	_objc_autoreleasePoolPush	leaq	L__unnamed_cfstring_(%rip), %rsi	movq	%rsi, %rdi	movq	%rax, -40(%rbp)         ## 8-byte Spill	movb	$0, %al// 调用 NSLog	callq	_NSLog	leaq	L_.str.1(%rip), %rsi	movq	%rsi, -24(%rbp)	movq	-24(%rbp), %rsi	leaq	L_.str.2(%rip), %rdi	movb	$0, %al// 调用 printf	callq	_printf	movq	L_OBJC_CLASSLIST_REFERENCES_$_(%rip), %rsi	movq	-24(%rbp), %rdx	movq	L_OBJC_SELECTOR_REFERENCES_(%rip), %rdi	movq	%rdi, -48(%rbp)         ## 8-byte Spill	movq	%rsi, %rdi	movq	-48(%rbp), %rsi         ## 8-byte Reload	movl	$4, %ecx	movl	%eax, -52(%rbp)         ## 4-byte Spill
    callq	*_objc_msgSend@GOTPCREL(%rip)	leaq	L__unnamed_cfstring_.4(%rip), %rcx	movq	%rax, -32(%rbp)	movq	-32(%rbp), %rsi	movq	%rcx, %rdi	movb	$0, %al
	callq	_NSLog	movq	-40(%rbp), %rdi         ## 8-byte Reload	callq	_objc_autoreleasePoolPop	xorl	%eax, %eax	addq	$64, %rsp	popq	%rbp	retq// main() 函数结束的地方	.cfi_endproc                                        ## -- End function	.section	__TEXT,__cstring,cstring_literalsL_.str:                                 ## @.str	.asciz	"Hello Clang Compile"

// clang -fmodules -c main.m -o main_obj.o// WYW:clang wangyongwangyongwang$ objdump -t main_obj.o
main_obj.o:	file format Mach-O 64-bit x86-64
SYMBOL TABLE:0000000000000140 l     O __TEXT,__ustring	l_.str.30000000000000000 g     F __TEXT,__text	_main0000000000000000         *UND*	_NSLog0000000000000000         *UND*	_OBJC_CLASS_$_NSString0000000000000000         *UND*	___CFConstantStringClassReference0000000000000000         *UND*	_objc_autoreleasePoolPop0000000000000000         *UND*	_objc_autoreleasePoolPush0000000000000000         *UND*	_objc_msgSend0000000000000000         *UND*	_printf

WYW:clang wangyongwangyongwang$ xcrun size -x -l -m main_obj.oSegment : 0x1c0 (vmaddr 0x0 fileoff 1488)	Section (__TEXT, __text): 0x9b (addr 0x0 offset 1488)	Section (__TEXT, __cstring): 0x2f (addr 0x9b offset 1643)	Section (__DATA, __cfstring): 0x40 (addr 0xd0 offset 1696)	Section (__DATA, __objc_classrefs): 0x8 (addr 0x110 offset 1760)	Section (__TEXT, __objc_methname): 0x1c (addr 0x118 offset 1768)	Section (__DATA, __objc_selrefs): 0x8 (addr 0x138 offset 1800)	Section (__TEXT, __ustring): 0x14 (addr 0x140 offset 1808)	Section (__DATA, __objc_imageinfo): 0x8 (addr 0x154 offset 1828)	Section (__LD, __compact_unwind): 0x20 (addr 0x160 offset 1840)	Section (__TEXT, __eh_frame): 0x40 (addr 0x180 offset 1872)	total 0x1b2total 0x1c0

WYW:clang wangyongwangyongwang$ xcrun otool -s __TEXT __text main_obj.omain_obj.o:Contents of (__TEXT,__text) section0000000000000000	55 48 89 e5 48 83 ec 40 89 7d fc 48 89 75 f0 e8 0000000000000010	00 00 00 00 48 8d 35 b5 00 00 00 48 89 f7 48 89 0000000000000020	45 d8 b0 00 e8 00 00 00 00 48 8d 35 7f 00 00 00 0000000000000030	48 89 75 e8 48 8b 75 e8 48 8d 3d 7d 00 00 00 b0 0000000000000040	00 e8 00 00 00 00 48 8b 35 c3 00 00 00 48 8b 55 0000000000000050	e8 48 8b 3d e0 00 00 00 48 89 7d d0 48 89 f7 48 0000000000000060	8b 75 d0 b9 04 00 00 00 89 45 cc ff 15 00 00 00 0000000000000070	00 48 8d 0d 78 00 00 00 48 89 45 e0 48 8b 75 e0 0000000000000080	48 89 cf b0 00 e8 00 00 00 00 48 8b 7d d8 e8 00 0000000000000090	00 00 00 31 c0 48 83 c4 40 5d c3

WYW:clang wangyongwangyongwang$ xcrun otool -v -t main_obj.omain_obj.o:(__TEXT,__text) section_main:0000000000000000	pushq	%rbp0000000000000001	movq	%rsp, %rbp0000000000000004	subq	$0x40, %rsp0000000000000008	movl	%edi, -0x4(%rbp)000000000000000b	movq	%rsi, -0x10(%rbp)000000000000000f	callq	0x140000000000000014	leaq	0xb5(%rip), %rsi000000000000001b	movq	%rsi, %rdi000000000000001e	movq	%rax, -0x28(%rbp)0000000000000022	movb	$0x0, %al0000000000000024	callq	0x290000000000000029	leaq	0x7f(%rip), %rsi0000000000000030	movq	%rsi, -0x18(%rbp)0000000000000034	movq	-0x18(%rbp), %rsi0000000000000038	leaq	0x7d(%rip), %rdi000000000000003f	movb	$0x0, %al0000000000000041	callq	0x460000000000000046	movq	0xc3(%rip), %rsi000000000000004d	movq	-0x18(%rbp), %rdx0000000000000051	movq	0xe0(%rip), %rdi0000000000000058	movq	%rdi, -0x30(%rbp)000000000000005c	movq	%rsi, %rdi000000000000005f	movq	-0x30(%rbp), %rsi0000000000000063	movl	$0x4, %ecx0000000000000068	movl	%eax, -0x34(%rbp)000000000000006b	callq	*(%rip)0000000000000071	leaq	0x78(%rip), %rcx0000000000000078	movq	%rax, -0x20(%rbp)000000000000007c	movq	-0x20(%rbp), %rsi0000000000000080	movq	%rcx, %rdi0000000000000083	movb	$0x0, %al0000000000000085	callq	0x8a000000000000008a	movq	-0x28(%rbp), %rdi000000000000008e	callq	0x930000000000000093	xorl	%eax, %eax0000000000000095	addq	$0x40, %rsp0000000000000099	popq	%rbp000000000000009a	retq

WYW:clang wangyongwangyongwang$ xcrun otool -s __TEXT __cstring main_obj.omain_obj.o:Contents of (__TEXT,__cstring) section000000000000009b	48 65 6c 6c 6f 20 43 6c 61 6e 67 20 43 6f 6d 70 00000000000000ab	69 6c 65 00 51 69 53 68 61 72 65 22 57 59 57 22 00000000000000bb	00 6d 65 6d 62 65 72 ef bc 9a 25 73 20 0a 00

// 生成执行文件WYW:clang wangyongwangyongwang$ clang main_obj.o -o mainExec
// 执行可执行文件WYW:clang wangyongwangyongwang$ ./mainExec2020-04-01 22:12:15.766 mainExec[84398:2934623] Hello Clang Compilemember：QiShare"WYW" 2020-04-01 22:12:15.767 mainExec[84398:2934623] member：QiShare"WYW"