1. 程式人生 > >【深入閱讀】關於LLVM,這些東西你必須知道!

【深入閱讀】關於LLVM,這些東西你必須知道!

只要你和程式碼打交道,瞭解編譯器的工作流程和原理定會讓你受益無窮,無論是分析程式,還是基於它寫自己的外掛,甚至學習一門全新的語音。通過本文,將帶你瞭解LLVM,並使用LLVM來完成一些有意思的事情。

一、什麼是LLVM?

The LLVM Project is a collection of modular and reusable compiler and toolchain technologies.

簡單來說,LLVM專案是一系列分模組、可重用的編譯工具鏈。它提供了一種程式碼編寫良好的中間表示(IR),可以作為多種語言的後端,還可以提供與變成語言無關的優化和針對多種cpu的程式碼生成功能。

先來看下LLVM架構的主要組成部分:

  • 前端:前端用來獲取原始碼然後將它轉變為某種中間表示,我們可以選擇不同的編譯器來作為LLVM的前端,如gcc,clang。
  • Pass(通常翻譯為“流程”):Pass用來將程式的中間表示之間相互變換。一般情況下,Pass可以用來優化程式碼,這部分通常是我們關注的部分。
  • 後端:後端用來生成實際的機器碼。

雖然如今大多數編譯器都採用的是這種架構,但是LLVM不同的就是對於不同的語言它都提供了同一種中間表示。傳統的編譯器的架構如下:

11script_1482136450962LLVM的架構如下:

12script_1482136601642當編譯器需要支援多種原始碼和目標架構時,基於LLVM的架構,設計一門新的語言只需要去實現一個新的前端就行了,支援新的後端架構也只需要實現一個新的後端就行了。其它部分完成可以複用,就不用再重新設計一次了。

二、安裝編譯LLVM

這裡使用clang作為前端:

2.svn獲取

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svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm

cd llvm/tools

svn co http://llvm.org/svn/llvm-project/cfe/trunk clang

cd ../projects

svn co http://llvm.org/svn/llvm-project/compiler-rt/trunk compiler-rt

cd ../tools/clang/tools

svn co http://llvm.org/svn/llvm-project/clang-tools-extra/trunk extra

3.git獲取

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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

最新的LLVM只支援cmake來編譯了,首先安裝cmake。

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brew install cmake

編譯:

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mkdir build

cmake /path/to/llvm/source

cmake --build .

編譯時間比較長,而且編譯結果會生成20G左右的檔案。

編譯完成後,就能在build/bin/目錄下面找到生成的工具了。

三、從原始碼到可執行檔案

我們在開發的時候的時候,如果想要生成一個可執行檔案或應用,我們點選run就完事了,那麼在點選run之後編譯器背後又做了哪些事情呢?

我們先來一個例子:

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#import <Foundation/Foundation.h>

#define TEN 10

int main(){

@autoreleasepool {

int numberOne = TEN;

int numberTwo = 8;

NSString* name = [[NSString alloc] initWithUTF8String:"AloneMonkey"];

int age = numberOne + numberTwo;

NSLog(@"Hello, %<a href="http://www.jobbole.com/members/Famous_god">@,</a> Age: %d", name, age);

}

return 0;

}

上面這個檔案,我們可以通過命令列直接編譯,然後連結:

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xcrun -sdk iphoneos clang -arch armv7 -F Foundation -fobjc-arc -c main.m -o main.o

xcrun -sdk iphoneos clang main.o -arch armv7 -fobjc-arc -framework Foundation -o main

拷貝到手機執行:

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monkeyde-iPhone:/tmp root# ./main

2016-12-19 17:16:34.654 main[2164:213100] Hello, AloneMonkey, Age: 18

大家不會以為就這樣就完了吧,當然不是,我們要繼續深入剖析。

3.1 預處理(Preprocess)

這部分包括macro巨集的展開,import/include標頭檔案的匯入,以及#if等處理。

可以通過執行以下命令,來告訴clang只執行到預處理這一步:

Objective-C

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clang -E main.m

執行完這個命令之後,我們會發現匯入了很多的標頭檔案內容。

Objective-C

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......

# 1 "/System/Library/Frameworks/Foundation.framework/Headers/FoundationLegacySwiftCompatibility.h" 1 3

# 185 "/System/Library/Frameworks/Foundation.framework/Headers/Foundation.h" 2 3

# 2 "main.m" 2

int main(){

@autoreleasepool {

int numberOne = 10;

int numberTwo = 8;

NSString* name = [[NSString alloc] initWithUTF8String:"AloneMonkey"];

int age = numberOne + numberTwo;

NSLog(@"Hello, %<a href="http://www.jobbole.com/members/Famous_god">@,</a> Age: %d", name, age);

}

return 0;

}

可以看到上面的預處理已經把巨集替換了,並且匯入了標頭檔案。但是這樣的話會引入很多不會去改變的系統庫比如Foundation,所以有了pch預處理檔案,可以在這裡去引入一些通用的標頭檔案。

後來Xcode新建的專案裡面去掉了pch檔案,引入了moduels的概念,把一些通用的庫打成modules的形式,然後匯入,預設會加上-fmodules引數。

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clang -E -fmodules main.m

這樣的話,只需要@import一下就能匯入對應庫的modules模組了。

Objective-C

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@import Foundation;

int main(){

@autoreleasepool {

int numberOne = 10;

int numberTwo = 8;

NSString* name = [[NSString alloc] initWithUTF8String:"AloneMonkey"];

int age = numberOne + numberTwo;

NSLog(@"Hello, %<a href="http://www.jobbole.com/members/Famous_god">@,</a> Age: %d", name, age);

}

return 0;

}

3.2 詞法分析 (Lexical Analysis)

在預處理之後,就要進行詞法分析了,將預處理過的程式碼轉化成一個個Token,比如左括號、右括號、等於、字串等等。

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

Objective-C

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annot_module_include '#import <F' Loc=<main.m:1:1>

int 'int' [StartOfLine] Loc=<main.m:5:1>

identifier 'main' [LeadingSpace] Loc=<main.m:5:5>

l_paren '(' Loc=<main.m:5:9>

r_paren ')' Loc=<main.m:5:10>

l_brace '{' Loc=<main.m:5:11>

at '@' [StartOfLine] [LeadingSpace] Loc=<main.m:6:5>

identifier 'autoreleasepool' Loc=<main.m:6:6>

l_brace '{' [LeadingSpace] Loc=<main.m:6:22>

int 'int' [StartOfLine] [LeadingSpace] Loc=<main.m:7:9>

identifier 'numberOne' [LeadingSpace] Loc=<main.m:7:13>

equal '=' [LeadingSpace] Loc=<main.m:7:23>

numeric_constant '10' [LeadingSpace] Loc=<main.m:7:25 <Spelling=main.m:3:13>>

semi ';' Loc=<main.m:7:28>

int 'int' [StartOfLine] [LeadingSpace] Loc=<main.m:8:9>

identifier 'numberTwo' [LeadingSpace] Loc=<main.m:8:13>

equal '=' [LeadingSpace] Loc=<main.m:8:23>

numeric_constant '8' [LeadingSpace] Loc=<main.m:8:25>

semi ';' Loc=<main.m:8:26>

identifier 'NSString' [StartOfLine] [LeadingSpace] Loc=<main.m:9:9>

star '*' Loc=<main.m:9:17>

identifier 'name' [LeadingSpace] Loc=<main.m:9:19>

equal '=' [LeadingSpace] Loc=<main.m:9:24>

l_square '[' [LeadingSpace] Loc=<main.m:9:26>

l_square '[' Loc=<main.m:9:27>

identifier 'NSString' Loc=<main.m:9:28>

identifier 'alloc' [LeadingSpace] Loc=<main.m:9:37>

r_square ']' Loc=<main.m:9:42>

identifier 'initWithUTF8String' [LeadingSpace] Loc=<main.m:9:44>

colon ':' Loc=<main.m:9:62>

string_literal '"AloneMonkey"' Loc=<main.m:9:63>

r_square ']' Loc=<main.m:9:76>

semi ';' Loc=<main.m:9:77>

int 'int' [StartOfLine] [LeadingSpace] Loc=<main.m:10:9>

identifier 'age' [LeadingSpace] Loc=<main.m:10:13>

equal '=' [LeadingSpace] Loc=<main.m:10:17>

identifier 'numberOne' [LeadingSpace] Loc=<main.m:10:19>

plus '+' [LeadingSpace] Loc=<main.m:10:29>

identifier 'numberTwo' [LeadingSpace] Loc=<main.m:10:31>

semi ';' Loc=<main.m:10:40>

identifier 'NSLog' [StartOfLine] [LeadingSpace] Loc=<main.m:11:9>

l_paren '(' Loc=<main.m:11:14>

at '@' Loc=<main.m:11:15>

string_literal '"Hello, %<a href="http://www.jobbole.com/members/Famous_god">@,</a> Age: %d"' Loc=<main.m:11:16>

comma ',' Loc=<main.m:11:36>

identifier 'name' [LeadingSpace] Loc=<main.m:11:38>

comma ',' Loc=<main.m:11:42>

identifier 'age' [LeadingSpace] Loc=<main.m:11:44>

r_paren ')' Loc=<main.m:11:47>

semi ';' Loc=<main.m:11:48>

r_brace '}' [StartOfLine] [LeadingSpace] Loc=<main.m:12:5>

return 'return' [StartOfLine] [LeadingSpace] Loc=<main.m:13:5>

numeric_constant '0' [LeadingSpace] Loc=<main.m:13:12>

semi ';' Loc=<main.m:13:13>

r_brace '}' [StartOfLine] Loc=<main.m:14:1>

eof '' Loc=<main.m:14:2>

3.3 語法分析 (Semantic Analysis)

根據當前語言的語法,驗證語法是否正確,並將所有節點組合成抽象語法樹(AST)

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

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......

`-FunctionDecl 0x7f8661d8a370 <main.m:5:1, line:14:1> line:5:5 main 'int ()'

`-CompoundStmt 0x7f8661d8aab0 <col:11, line:14:1>

|-ObjCAutoreleasePoolStmt 0x7f8661d8aa68 <line:6:5, line:12:5>

| `-CompoundStmt 0x7f8661d8aa28 <line:6:22, line:12:5>

| |-DeclStmt 0x7f8661d8a4a0 <line:7:9, col:28>

| | `-VarDecl 0x7f8661d8a420 <col:9, line:3:13> line:7:13 used numberOne 'int' cinit

| | `-IntegerLiteral 0x7f8661d8a480 <line:3:13> 'int' 10

| |-DeclStmt 0x7f8661d8a550 <line:8:9, col:26>

| | `-VarDecl 0x7f8661d8a4d0 <col:9, col:25> col:13 used numberTwo 'int' cinit

| | `-IntegerLiteral 0x7f8661d8a530 <col:25> 'int' 8

| |-DeclStmt 0x7f8661d8a6c0 <line:9:9, col:77>

| | `-VarDecl 0x7f8661d8a580 <col:9, col:76> col:19 used name 'NSString *' cinit

| | `-ObjCMessageExpr 0x7f8661d8a688 <col:26, col:76> 'NSString * _Nullable':'NSString *' selector=initWithUTF8String:

| | |-ObjCMessageExpr 0x7f8661d8a5f0 <col:27, col:42> 'NSString *' selector=alloc class='NSString'

| | `-ImplicitCastExpr 0x7f8661d8a670 <col:63> 'const char * _Nonnull':'const char *' <BitCast>

| | `-ImplicitCastExpr 0x7f8661d8a658 <col:63> 'char *' <ArrayToPointerDecay>

| | `-StringLiteral 0x7f8661d8a620 <col:63> 'char [12]' lvalue "AloneMonkey"

| |-DeclStmt 0x7f8661d8a7f8 <line:10:9, col:40>

| | `-VarDecl 0x7f8661d8a6f0 <col:9, col:31> col:13 used age 'int' cinit

| | `-BinaryOperator 0x7f8661d8a7d0 <col:19, col:31> 'int' '+'

| | |-ImplicitCastExpr 0x7f8661d8a7a0 <col:19> 'int' <LValueToRValue>

| | | `-DeclRefExpr 0x7f8661d8a750 <col:19> 'int' lvalue Var 0x7f8661d8a420 'numberOne' 'int'

| | `-ImplicitCastExpr 0x7f8661d8a7b8 <col:31> 'int' <LValueToRValue>

| | `-DeclRefExpr 0x7f8661d8a778 <col:31> 'int' lvalue Var 0x7f8661d8a4d0 'numberTwo' 'int'

| `-CallExpr 0x7f8661d8a9a0 <line:11:9, col:47> 'void'

| |-ImplicitCastExpr 0x7f8661d8a988 <col:9> 'void (*)(id, ...)' <FunctionToPointerDecay>

| | `-DeclRefExpr 0x7f8661d8a810 <col:9> 'void (id, ...)' Function 0x7f86618df0e0 'NSLog' 'void (id, ...)'

| |-ImplicitCastExpr 0x7f8661d8a9e0 <col:15, col:16> 'id':'id' <BitCast>

| | `-ObjCStringLiteral 0x7f8661d8a8b8 <col:15, col:16> 'NSString *'

| | `-StringLiteral 0x7f8661d8a878 <col:16> 'char [19]' lvalue "Hello, %<a href="http://www.jobbole.com/members/Famous_god">@,</a> Age: %d"

| |-ImplicitCastExpr 0x7f8661d8a9f8 <col:38> 'NSString *' <LValueToRValue>

| | `-DeclRefExpr 0x7f8661d8a8d8 <col:38> 'NSString *' lvalue Var 0x7f8661d8a580 'name' 'NSString *'

| `-ImplicitCastExpr 0x7f8661d8aa10 <col:44> 'int' <LValueToRValue>

| `-DeclRefExpr 0x7f8661d8a900 <col:44> 'int' lvalue Var 0x7f8661d8a6f0 'age' 'int'

`-ReturnStmt 0x7f8661d8aa98 <line:13:5, col:12>

`-IntegerLiteral 0x7f8661d8aa78 <col:12> 'int' 0

語法樹直觀圖:

13script_1482150626825

3.4 IR程式碼生成 (CodeGen)

CodeGen負責將語法樹從頂至下遍歷,翻譯成LLVM IR,LLVM IR是Frontend的輸出,也是LLVM Backerend的輸入,橋接前後端。

可以在中間程式碼層次去做一些優化工作,我們在Xcode的編譯設定裡面也可以設定優化級別-O1,-O3,-Os。 還可以去寫一些自己的Pass,這裡需要解釋一下什麼是Pass。

Pass就是LLVM系統轉化和優化的工作的一個節點,每個節點做一些工作,這些工作加起來就構成了LLVM整個系統的優化和轉化。

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

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......

; Function Attrs: ssp uwtable

define i32 @main() #0 {

entry:

%retval = alloca i32, align 4

%numberOne = alloca i32, align 4

%numberTwo = alloca i32, align 4

%name = alloca %0*, align 8

%age = alloca i32, align 4

store i32 0, i32* %retval, align 4

%0 = call i8* @objc_autoreleasePoolPush() #3

store i32 10, i32* %numberOne, align 4

store i32 8, i32* %numberTwo, align 4

%1 = load %struct._class_t*, %struct._class_t** @"OBJC_CLASSLIST_REFERENCES_$_", align 8

%2 = load i8*, i8** @OBJC_SELECTOR_REFERENCES_, align 8, !invariant.load !7

%3 = bitcast %struct._class_t* %1 to i8*

%call = call i8* bitcast (i8* (i8*, i8*, ...)* @objc_msgSend to i8* (i8*, i8*)*)(i8* %3, i8* %2)

%4 = bitcast i8* %call to %0*

%5 = load i8*, i8** @OBJC_SELECTOR_REFERENCES_.2, align 8, !invariant.load !7

%6 = bitcast %0* %4 to i8*

%call1 = call i8* bitcast (i8* (i8*, i8*, ...)* @objc_msgSend to i8* (i8*, i8*, i8*)*)(i8* %6, i8* %5, i8* getelementptr inbounds ([12 x i8], [12 x i8]* @.str, i32 0, i32 0))

%7 = bitcast i8* %call1 to %0*

store %0* %7, %0** %name, align 8

%8 = load i32, i32* %numberOne, align 4

%9 = load i32, i32* %numberTwo, align 4

%10 = sub i32 0, %9

%11 = sub nsw i32 %8, %10

%add = add nsw i32 %8, %9

store i32 %11, i32* %age, align 4

%12 = load %0*, %0** %name, align 8

%13 = load i32, i32* %age, align 4

notail call void (i8*, ...) @NSLog(i8* bitcast (%struct.__NSConstantString_tag* @_unnamed_cfstring_ to i8*), %0* %12, i32 %13)

%14 = bitcast %0** %name to i8**

call void @objc_storeStrong(i8** %14, i8* null) #3

call void @objc_autoreleasePoolPop(i8* %0)

ret i32 0

}

declare i8* @objc_autoreleasePoolPush()

; Function Attrs: nonlazybind

declare i8* @objc_msgSend(i8*, i8*, ...) #1

declare void @NSLog(i8*, ...) #2

declare void @objc_storeStrong(i8**, i8*)

declare void @objc_autoreleasePoolPop(i8*)

......

!6 = !{!"clang version 4.0.0 (trunk 289913) (llvm/trunk 289911)"}

!7 = !{}

3.5 生成位元組碼 (LLVM Bitcode)

我們在Xcode7中預設生成bitcode就是這種的中間形式存在, 開啟了bitcode,那麼蘋果後臺拿到的就是這種中間程式碼,蘋果可以對bitcode做一個進一步的優化,如果有新的後端架構,仍然可以用這份bitcode去生成。

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14script_1482218230417

3.6 生成相關彙編

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.section __TEXT,__text,regular,pure_instructions

.macosx_version_min 10, 12

.globl _main

.p2align 4, 0x90

_main: ## <a href="http://www.jobbole.com/members/wx943357207">@main</a>

.cfi_startproc

## BB#0: ## %entry

pushq %rbp

Lcfi0:

.cfi_def_cfa_offset 16

Lcfi1:

.cfi_offset %rbp, -16

movq %rsp, %rbp

Lcfi2:

.cfi_def_cfa_register %rbp

subq $48, %rsp

movl $0, -4(%rbp)

callq _objc_autoreleasePoolPush

movl $10, -8(%rbp)

movl $8, -12(%rbp)

movq L_OBJC_CLASSLIST_REFERENCES_$_(%rip), %rcx

movq L_OBJC_SELECTOR_REFERENCES_(%rip), %rsi

movq %rcx, %rdi

movq %rax, -40(%rbp) ## 8-byte Spill

callq _objc_msgSend

leaq L_.str(%rip), %rdx

movq L_OBJC_SELECTOR_REFERENCES_.2(%rip), %rsi

movq %rax, %rdi

callq _objc_msgSend

leaq L__unnamed_cfstring_(%rip), %rcx

xorl %r8d, %r8d

movq %rax, -24(%rbp)

movl -8(%rbp), %r9d

movl -12(%rbp), %r10d

subl %r10d, %r8d

subl %r8d, %r9d

movl %r9d, -28(%rbp)

movq -24(%rbp), %rsi

movl -28(%rbp), %edx

movq %rcx, %rdi

movb $0, %al

callq _NSLog

xorl %edx, %edx

movl %edx, %esi

leaq -24(%rbp), %rcx

movq %rcx, %rdi

callq _objc_storeStrong

movq -40(%rbp), %rdi ## 8-byte Reload

callq _objc_autoreleasePoolPop

xorl %eax, %eax

addq $48, %rsp

popq %rbp

retq

.cfi_endproc

.section __DATA,__objc_classrefs,regular,no_dead_strip

.p2align 3 ## @"OBJC_CLASSLIST_REFERENCES_$_"

L_OBJC_CLASSLIST_REFERENCES_$_:

.quad _OBJC_CLASS_$_NSString

.section __TEXT,__objc_methname,cstring_literals

L_OBJC_METH_VAR_NAME_: ## @OBJC_METH_VAR_NAME_

.asciz "alloc"

.section __DATA,__objc_selrefs,literal_pointers,no_dead_strip

.p2align 3 ## @OBJC_SELECTOR_REFERENCES_

L_OBJC_SELECTOR_REFERENCES_:

.quad L_OBJC_METH_VAR_NAME_

.section __TEXT,__cstring,cstring_literals

L_.str: ## @.str

.asciz "AloneMonkey"

.section __TEXT,__objc_methname,cstring_literals

L_OBJC_METH_VAR_NAME_.1: ## @OBJC_METH_VAR_NAME_.1

.asciz "initWithUTF8String:"

.section __DATA,__objc_selrefs,literal_pointers,no_dead_strip

.p2align 3 ## @OBJC_SELECTOR_REFERENCES_.2

L_OBJC_SELECTOR_REFERENCES_.2:

.quad L_OBJC_METH_VAR_NAME_.1

.section __TEXT,__cstring,cstring_literals

L_.str.3: ## @.str.3

.asciz "Hello, %<a href="http://www.jobbole.com/members/Famous_god">@,</a> Age: %d"

.section __DATA,__cfstring

.p2align 3 ## @_unnamed_cfstring_

L__unnamed_cfstring_:

.quad ___CFConstantStringClassReference

.long 1992 ## 0x7c8

.space 4

.quad L_.str.3

.quad 18 ## 0x12

.section __DATA,__objc_imageinfo,regular,no_dead_strip

L_OBJC_IMAGE_INFO:

.long 0

.long 64

.subsections_via_symbols

3.7 生成目標檔案

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clang -fmodules -c main.m -o main.o

15script_1482218636504

3.8 生成可執行檔案

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clang main.o -o main

./main

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2016-12-20 15:25:42.299 main[8941:327306] Hello, AloneMonkey, Age: 18

3.9 整體流程

16script_1482219005958

四、可以用Clang做什麼?

4.1 libclang進行語法分析

可以使用libclang裡面提供的方法對原始檔進行語法分析,分析它的語法樹,遍歷語法樹上面的每一個節點。可以用於檢查拼寫錯誤,或者做字串加密。

來看一段程式碼的使用:

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void *hand = dlopen("/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/libclang.dylib",RTLD_LAZY);

//初始化函式指標

initlibfunclist(hand);

CXIndex cxindex = myclang_createIndex(1, 1);

const char *filename = "/path/to/filename";

int index = 0;

const char ** new_command = malloc(10240);

NSMutableString *mus = [NSMutableString stringWithString:@"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -x objective-c -arch armv7 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk"];

NSArray *arr = [mus componentsSeparatedByString:@" "];

for (NSString *tmp in arr) {

new_command[index++] = [tmp UTF8String];

}

nameArr = [[NSMutableArray alloc] initWithCapacity:10];

TU = myclang_parseTranslationUnit(cxindex, filename, new_command, index, NULL, 0, myclang_defaultEditingTranslationUnitOptions());

CXCursor rootCursor = myclang_getTranslationUnitCursor(TU);

myclang_visitChildren(rootCursor, printVisitor, NULL);

myclang_disposeTranslationUnit(TU);

myclang_disposeIndex(cxindex);

free(new_command);

dlclose(hand);

然後我們就可以在printVisitor這個函式裡面去遍歷輸入檔案的語法樹了。

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2016-12-20 16:25:44.006588 ParseClangLib[9525:368452] showString

int main(){

@autoreleasepool {

int numberOne = TEN;

int numberTwo = 8;

NSString* name = [[NSString alloc] initWithUTF8String:"AloneMonkey"];

int age = numberOne + numberTwo;

NSLog(@"Hello, %<a href="http://www.jobbole.com/members/Famous_god">@,</a> Age: %d", name, age);

}

return 0;

}

2016-12-20 16:25:44.007101 ParseClangLib[9525:368452] disname is main()

2016-12-20 16:25:44.007142 ParseClangLib[9525:368452] ccurkind is =>FunctionDecl

2016-12-20 16:25:44.007180 ParseClangLib[9525:368452] 繼續遍歷孩子節點main()

2016-12-20 16:25:44.007236 ParseClangLib[9525:368452] showString

{

@autoreleasepool {

int numberOne = TEN;

int numberTwo = 8;

NSString* name = [[NSString alloc] initWithUTF8String:"AloneMonkey"];

int age = numberOne + numberTwo;

NSLog(@"Hello, %<a href="http://www.jobbole.com/members/Famous_god">@,</a> Age: %d", name, age);

}

return 0;

}

2016-12-20 16:25:44.007253 ParseClangLib[9525:368452] disname is

2016-12-20 16:25:44.007263 ParseClangLib[9525:368452] ccurkind is =>CompoundStmt

2016-12-20 16:25:44.007274 ParseClangLib[9525:368452] 繼續遍歷孩子節點

2016-12-20 16:25:44.007309 ParseClangLib[9525:368452] showString

@autoreleasepool {

int numberOne = TEN;

int numberTwo = 8;

NSString* name = [[NSString alloc] initWithUTF8String:"AloneMonkey"];

int age = numberOne + numberTwo;

NSLog(@"Hello, %<a href="http://www.jobbole.com/members/Famous_god">@,</a> Age: %d", name, age);

}

2016-12-20 16:25:44.007424 ParseClangLib[9525:368452] disname is

2016-12-20 16:25:44.007442 ParseClangLib[9525:368452] ccurkind is =>ObjCAutoreleasePoolStmt

2016-12-20 16:25:44.007455 ParseClangLib[9525:368452] 繼續遍歷孩子節點

2016-12-20 16:25:44.007488 ParseClangLib[9525:368452] showString

{

int numberOne = TEN;

int numberTwo = 8;

NSString* name = [[NSString alloc] initWithUTF8String:"AloneMonkey"];

int age = numberOne + numberTwo;

NSLog(@"Hello, %<a href="http://www.jobbole.com/members/Famous_god">@,</a> Age: %d", name, age);

}

2016-12-20 16:25:44.007504 ParseClangLib[9525:368452] disname is

2016-12-20 16:25:44.007514 ParseClangLib[9525:368452] ccurkind is =>CompoundStmt

2016-12-20 16:25:44.007525 ParseClangLib[9525:368452] 繼續遍歷孩子節點

2016-12-20 16:25:44.007553 ParseClangLib[9525:368452] showString

int numberOne = TEN;

2016-12-20 16:25:44.007565 ParseClangLib[9525:368452] disname is

2016-12-20 16:25:44.007574 ParseClangLib[9525:368452] ccurkind is =>DeclStmt

2016-12-20 16:25:44.013133 ParseClangLib[9525:368452] 繼續遍歷孩子節點

2016-12-20 16:25:44.013206 ParseClangLib[9525:368452] showString

int numberOne = TEN

.......

2016-12-20 16:25:44.015848 ParseClangLib[9525:368452] ccurkind is =>ObjCStringLiteral

2016-12-20 16:25:44.015858 ParseClangLib[9525:368452] OC 字串

2016-12-20 16:25:44.015876 ParseClangLib[9525:368452] showString

@"Hello, %<a href="http://www.jobbole.com/members/Famous_god">@,</a> Age: %d"

2016-12-20 16:25:44.015932 ParseClangLib[9525:368452] showString

name

2016-12-20 16:25:44.015973 ParseClangLib[9525:368452] disname is name

2016-12-20 16:25:44.015997 ParseClangLib[9525:368452] ccurkind is =>UnexposedExpr

2016-12-20 16:25:44.016013 ParseClangLib[9525:368452] 繼續遍歷孩子節點name

2016-12-20 16:25:44.016039 ParseClangLib[9525:368452] showString

name

2016-12-20 16:25:44.016051 ParseClangLib[9525:368452] disname is name

2016-12-20 16:25:44.016060 ParseClangLib[9525:368452] ccurkind is =>DeclRefExpr

2016-12-20 16:25:44.016071 ParseClangLib[9525:368452] 繼續遍歷孩子節點

2016-12-20 16:25:44.016137 ParseClangLib[9525:368452] showString

age

2016-12-20 16:25:44.016160 ParseClangLib[9525:368452] disname is age

2016-12-20 16:25:44.016170 ParseClangLib[9525:368452] ccurkind is =>UnexposedExpr

2016-12-20 16:25:44.016183 ParseClangLib[9525:368452] 繼續遍歷孩子節點

2016-12-20 16:25:44.016213 ParseClangLib[9525:368452] showString

age

2016-12-20 16:25:44.016256 ParseClangLib[9525:368452] disname is age

2016-12-20 16:25:44.016279 ParseClangLib[9525:368452] ccurkind is =>DeclRefExpr

2016-12-20 16:25:44.016293 ParseClangLib[9525:368452] 繼續遍歷孩子節點age

2016-12-20 16:25:44.016318 ParseClangLib[9525:368452] showString

return 0

2016-12-20 16:25:44.016330 ParseClangLib[9525:368452] disname is

2016-12-20 16:25:44.016339 ParseClangLib[9525:368452] ccurkind is =>ReturnStmt

2016-12-20 16:25:44.016350 ParseClangLib[9525:368452] 繼續遍歷孩子節點

2016-12-20 16:25:44.016369 ParseClangLib[9525:368452] showString

0

2016-12-20 16:25:44.016408 ParseClangLib[9525:368452] disname is

2016-12-20 16:25:44.016445 ParseClangLib[9525:368452] ccurkind is =>IntegerLiteral

2016-12-20 16:25:44.016461 ParseClangLib[9525:368452] 繼續遍歷孩子節點

我們也通過通過python去呼叫用clang:

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pip install clang

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#!/usr/bin/python

# vim: set fileencoding=utf-8

import clang.cindex

import asciitree

import sys

def node_children(node):

return (c for c in node.get_children() if c.location.file == sys.argv[1])

def print_node(node):

text = node.spelling or node.displayname

kind = str(node.kind)[str(node.kind).index('.')+1:]

return '{} {}'.format(kind, text)

if len(sys.argv) != 2:

print("Usage: dump_ast.py [header file name]")

sys.exit()

clang.cindex.Config.set_library_file('/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/libclang.dylib')

index = clang.cindex.Index.create()

translation_unit = index.parse(sys.argv[1], ['-x', 'objective-c'])

print asciitree.draw_tree(translation_unit.cursor,

lambda n: list(n.get_children()),

lambda n: "%s (%s)" % (n.spelling or n.displayname, str(n.kind).split(".")[1]))

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.......

+--main (FUNCTION_DECL)

+-- (COMPOUND_STMT)

+-- (OBJC_AUTORELEASE_POOL_STMT)

| +-- (COMPOUND_STMT)

| +-- (DECL_STMT)

| | +--numberOne (VAR_DECL)

| | +-- (INTEGER_LITERAL)

| +-- (DECL_STMT)

| | +--numberTwo (VAR_DECL)

| | +-- (INTEGER_LITERAL)

| +-- (DECL_STMT)

| | +--name (VAR_DECL)

| | +--NSString (OBJC_CLASS_REF)

| | +--initWithUTF8String: (OBJC_MESSAGE_EXPR)

| | +--alloc (OBJC_MESSAGE_EXPR)

| | | +--NSString (OBJC_CLASS_REF)

| | +-- (UNEXPOSED_EXPR)

| | +-- (UNEXPOSED_EXPR)

| | +--"AloneMonkey" (STRING_LITERAL)

| +-- (DECL_STMT)

| | +--age (VAR_DECL)

| | +-- (BINARY_OPERATOR)

| | +--numberOne (UNEXPOSED_EXPR)

| | | +--numberOne (DECL_REF_EXPR)

| | +--numberTwo (UNEXPOSED_EXPR)

| | +--numberTwo (DECL_REF_EXPR)

| +--NSLog (CALL_EXPR)

| +--NSLog (UNEXPOSED_EXPR)

| | +--NSLog (DECL_REF_EXPR)

| +-- (UNEXPOSED_EXPR)

| | +--"Hello, %<a href="http://www.jobbole.com/members/Famous_god">@,</a> Age: %d" (OBJC_STRING_LITERAL)

| | +--"Hello, %<a href="http://www.jobbole.com/members/Famous_god">@,</a> Age: %d" (STRING_LITERAL)

| +--name (UNEXPOSED_EXPR)

| | +--name (DECL_REF_EXPR)

| +--age (UNEXPOSED_EXPR)

| +--age (DECL_REF_EXPR)

+-- (RETURN_STMT)

+-- (INTEGER_LITERAL)

那麼基於語法樹的分析,我們可以針對字串做加密:

11859001-2f61aa201798594e

從左上角的明文字串,處理成右下角的介個樣子~

4.2 LibTooling

對語法樹有完全的控制權,可以作為一個單獨的命令使用,如:clang-format

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clang-format main.m

我們也可以自己寫一個這樣的工具去遍歷、訪問、甚至修改語法樹。 目錄:llvm/tools/clang/tools

Objective-C

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#include "clang/Driver/Options.h"

#include "clang/AST/AST.h"

#include "clang/AST/ASTContext.h"

#include "clang/AST/ASTConsumer.h"

#include "clang/AST/RecursiveASTVisitor.h"

#include "clang/Frontend/ASTConsumers.h"

#include "clang/Frontend/FrontendActions.h"

#include "clang/Frontend/CompilerInstance.h"

#include "clang/Tooling/CommonOptionsParser.h"

#include "clang/Tooling/Tooling.h"

#include "clang/Rewrite/Core/Rewriter.h"

using namespace std;

using namespace clang;

using namespace clang::driver;

using namespace clang::tooling;

using namespace llvm;

Rewriter rewriter;

int numFunctions = 0;

static llvm::cl::OptionCategory StatSampleCategory("Stat Sample");

class ExampleVisitor : public RecursiveASTVisitor<ExampleVisitor> {

private:

ASTContext *astContext; // used for getting additional AST info

public:

explicit ExampleVisitor(CompilerInstance *CI)

: astContext(&(CI->getASTContext())) // initialize private members

{

rewriter.setSourceMgr(astContext->getSourceManager(), astContext->getLangOpts());

}

virtual bool VisitFunctionDecl(FunctionDecl *func) {

numFunctions++;

string funcName = func->getNameInfo().getName().getAsString();

if (funcName == "do_math") {

rewriter.ReplaceText(func->getLocation(), funcName.length(), "add5");

errs() << "** Rewrote function def: " << funcName << "\n";

}

return true;

}

virtual bool VisitStmt(Stmt *st) {

if (ReturnStmt *ret = dyn_cast<ReturnStmt>(st)) {

rewriter.ReplaceText(ret->getRetValue()->getLocStart(), 6, "val");

errs() << "** Rewrote ReturnStmt\n";

}

if (CallExpr *call = dyn_cast<CallExpr>(st)) {

rewriter.ReplaceText(call->getLocStart(), 7, "add5");

errs() << "** Rewrote function call\n";

}

return true;

}

};

class ExampleASTConsumer : public ASTConsumer {

private:

ExampleVisitor *visitor; // doesn't have to be private

public:

// override the constructor in order to pass CI

explicit ExampleASTConsumer(CompilerInstance *CI)

: visitor(new ExampleVisitor(CI)) // initialize the visitor

{ }

// override this to call our ExampleVisitor on the entire source file

virtual void HandleTranslationUnit(ASTContext &Context) {

visitor->TraverseDecl(Context.getTranslationUnitDecl());

}

};

class ExampleFrontendAction : public ASTFrontendAction {

public:

virtual std::unique_ptr<ASTConsumer> CreateASTConsumer(CompilerInstance &CI, StringRef file) {

return llvm::make_unique<ExampleASTConsumer>(&CI); // pass CI pointer to ASTConsumer

}

};

int main(int argc, const char **argv) {

// parse the command-line args passed to your code

CommonOptionsParser op(argc, argv, StatSampleCategory);

// create a new Clang Tool instance (a LibTooling environment)

ClangTool Tool(op.getCompilations(), op.getSourcePathList());

// run the Clang Tool, creating a new FrontendAction (explained below)

int result = Tool.run(newFrontendActionFactory<ExampleFrontendAction>().get());

errs() << "\nFound " << numFunctions << " functions.\n\n";

// print out the rewritten source code ("rewriter" is a global var.)

rewriter.getEditBuffer(rewriter.getSourceMgr().getMainFileID()).write(errs());

return result;

}

上面的程式碼通過遍歷語法樹,去修改裡面的方法名和返回變數名:

Objective-C

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before:

void do_math(int *x) {

*x += 5;

}

int main(void) {

int result = -1, val = 4;

do_math(&val);

return result;

}

after:

** Rewrote function def: do_math

** Rewrote function call

** Rewrote ReturnStmt

Found 2 functions.

void add5(int *x) {

*x += 5;

}

int main(void) {

int result = -1, val = 4;

add5(&val);

return val;

}

那麼,我們看到LibTooling對程式碼的語法樹有完全的控制,那麼我們可以基於它去檢查命名的規範,甚至做一個程式碼的轉換,比如實現OC轉Swift。

4.3 ClangPlugin

對語法樹有完全的控制權,作為外掛注入到編譯流程中,可以影響build和決定編譯過程。目錄:llvm/tools/clang/examples

Objective-C

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#include "clang/Driver/Options.h"

#include "clang/AST/AST.h"

#include "clang/AST/ASTContext.h"

#include "clang/AST/ASTConsumer.h"

#include "clang/AST/RecursiveASTVisitor.h"

#include "clang/Frontend/ASTConsumers.h"

#include "clang/Frontend/FrontendActions.h"

#include "clang/Frontend/CompilerInstance.h"

#include "clang/Frontend/FrontendPluginRegistry.h"

#include "clang/Rewrite/Core/Rewriter.h"

using namespace std;

using namespace clang;

using namespace llvm;

Rewriter rewriter;

int numFunctions = 0;

class ExampleVisitor : public RecursiveASTVisitor<ExampleVisitor> {

private:

ASTContext *astContext; // used for getting additional AST info

public:

explicit ExampleVisitor(CompilerInstance *CI)

: astContext(&(CI->getASTContext())) // initialize private members

{

rewriter.setSourceMgr(astContext->getSourceManager(), astContext->getLangOpts());

}

virtual bool VisitFunctionDecl(FunctionDecl *func) {

numFunctions++;

string funcName = func->getNameInfo().getName().getAsString();

if (funcName == "do_math") {

rewriter.ReplaceText(func->getLocation(), funcName.length(), "add5");

errs() << "** Rewrote function def: " << funcName << "\n";

}

return true;

}

virtual bool VisitStmt(Stmt *st) {

if (ReturnStmt *ret = dyn_cast<ReturnStmt>(st)) {

rewriter.ReplaceText(ret->getRetValue()->getLocStart(), 6, "val");

errs() << "** Rewrote ReturnStmt\n";

}

if (CallExpr *call = dyn_cast<CallExpr>(st)) {

rewriter.ReplaceText(call->getLocStart(), 7, "add5");

errs() << "** Rewrote function call\n";

}

return true;

}

};

class ExampleASTConsumer : public ASTConsumer {

private:

ExampleVisitor *visitor; // doesn't have to be private

public:

// override the constructor in order to pass CI

explicit ExampleASTConsumer(CompilerInstance *CI):

visitor(new ExampleVisitor(CI)) { } // initialize the visitor

// override this to call our ExampleVisitor on the entire source file

virtual void HandleTranslationUnit(ASTContext &Context) {

/* we can use ASTContext to get the TranslationUnitDecl, which is

a single Decl that collectively represents the entire source file */

visitor->TraverseDecl(Context.getTranslationUnitDecl());

}

};

class PluginExampleAction : public PluginASTAction {

protected:

// this gets called by Clang when it invokes our Plugin

// Note that unique pointer is used here.

std::unique_ptr<ASTConsumer> CreateASTConsumer(CompilerInstance &CI, StringRef file) {

return llvm::make_unique<ExampleASTConsumer>(&CI);

}

// implement this function if you want to parse custom cmd-line args

bool ParseArgs(const CompilerInstance &CI, const vector<string> &args) {

return true;

}

};

static FrontendPluginRegistry::Add<PluginExampleAction> X("-example-plugin", "simple Plugin example");

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clang -Xclang -load -Xclang ../build/lib/PluginExample.dylib -Xclang -plugin -Xclang -example-plugin -c testPlugin.c

** Rewrote function def: do_math

** Rewrote function call

** Rewrote ReturnStmt

我們可以基於ClangPlugin做些什麼事情呢?我們可以用來定義一些編碼規範,比如程式碼風格檢查,命名檢查等等。下面是我寫的判斷類名前兩個字母是不是大寫的例子,如果不是報錯。(當然這只是一個例子而已。。。)

18script_1482318703701

五、動手寫Pass

5.1 一個簡單的Pass

前面我們說到,Pass就是LLVM系統轉化和優化的工作的一個節點,當然我們也可以寫一個這樣的節點去做一些自己的優化工作或者其它的操作。下面我們來看一下一個簡單Pass的編寫流程:

1.建立標頭檔案

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cd llvm/include/llvm/Transforms/

mkdir Obfuscation

cd Obfuscation

touch SimplePass.h

寫入內容:

Objective-C

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#include "llvm/IR/Function.h"

#include "llvm/Pass.h"

#include "llvm/Support/raw_ostream.h"

#include "llvm/IR/Intrinsics.h"

#include "llvm/IR/Instructions.h"

#include "llvm/IR/LegacyPassManager.h"

#include "llvm/Transforms/IPO/PassManagerBuilder.h"

// Namespace

using namespace std;

namespace llvm {

Pass *createSimplePass(bool flag);

}

2.建立原始檔

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cd llvm/lib/Transforms/

mkdir Obfuscation

cd Obfuscation

touch CMakeLists.txt

touch LLVMBuild.txt

touch SimplePass.cpp

CMakeLists.txt:

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add_llvm_loadable_module(LLVMObfuscation

  SimplePass.cpp

  )

  add_dependencies(LLVMObfuscation intrinsics_gen)

LLVMBuild.txt:

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[component_0]

type = Library

name = Obfuscation

parent = Transforms

library_name = Obfuscation

SimplePass.cpp:

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#include "llvm/Transforms/Obfuscation/SimplePass.h"

using namespace llvm;

namespace {

struct SimplePass : public FunctionPass {

static char ID; // Pass identification, replacement for typeid

bool flag;

SimplePass() : FunctionPass(ID) {}

SimplePass(bool flag) : FunctionPass(ID) {

this->flag = flag;

}

bool runOnFunction(Function &F) override {

if(this->flag){

Function *tmp = &F;

// 遍歷函式中的所有基本塊

for (Function::iterator bb = tmp->begin(); bb != tmp->end(); ++bb) {

// 遍歷基本塊中的每條指令

for (BasicBlock::iterator inst = bb->begin(); inst != bb->end(); ++inst) {

// 是否是add指令

if (inst->isBinaryOp()) {

if (inst->getOpcode() == Instruction::Add) {

ob_add(cast<BinaryOperator>(inst));

}

}

}

}

}

return false;

}

// a+b === a-(-b)

void ob_add(BinaryOperator *bo) {

BinaryOperator *op = NULL;

if (bo->getOpcode() == Instruction::Add) {

// 生成 (-b)

op = BinaryOperator::CreateNeg(bo->getOperand(1), "", bo);

// 生成 a-(-b)

op = BinaryOperator::Create(Instruction::Sub, bo->getOperand(0), op, "", bo);

op->setHasNoSignedWrap(bo->hasNoSignedWrap());

op->setHasNoUnsignedWrap(bo->hasNoUnsignedWrap());

}

// 替換所有出現該指令的地方

bo->replaceAllUsesWith(op);

}

};

}

char SimplePass::ID = 0;

// 註冊pass 命令列選項顯示為simplepass

static RegisterPass<SimplePass> X("simplepass", "this is a Simple Pass");

Pass *llvm::createSimplePass() { return new SimplePass(); }

修改.../Transforms/LLVMBuild.txt, 加上剛剛寫的模組Obfuscation

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subdirectories = Coroutines IPO InstCombine Instrumentation Scalar Utils Vectorize ObjCARC Obfuscation

修改.../Transforms/CMakeLists.txt, 加上剛剛寫的模組Obfuscation

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add_subdirectory(Obfuscation)

編譯生成:LLVMSimplePass.dylib

因為Pass是作用於中間程式碼,所以我們首先要生成一份中間程式碼:

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clang -emit-llvm -c test.c -o test.bc

然後載入Pass優化:

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../build/bin/opt -load ../build/lib/LLVMSimplePass.dylib -test < test.bc > after_test.bc

對比中間程式碼:

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llvm-dis test.bc -o test.ll

llvm-dis after_test.bc -o after_test.ll

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test.ll

......

entry:

%retval = alloca i32, align 4

%a = alloca i32, align 4

%b = alloca i32, align 4

%c = alloca i32, align 4

store i32 0, i32* %retval, align 4

store i32 3, i32* %a, align 4

store i32 4, i32* %b, align 4

%0 = load i32, i32* %a, align 4

%1 = load i32, i32* %b, align 4

%add = add nsw i32 %0, %1

store i32 %add, i32* %c, align 4

%2 = load i32, i32* %c, align 4

%call = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str, i32 0, i32 0), i32 %2)

ret i32 0

}

......

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