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iOS高级强化--004：Symbol

杰克逊爱学习 2021-09-23 阅读 36
iOS高级强化
  • Symbol Table：⽤来保存符号。
  • String Table：⽤来保存符号的名称。
  • Indirect Symbol Table：间接符号表。保存使⽤的外部符号。更准确⼀点就是使⽤的外部动态库的符号。是Symbol Table的子集。
LC_SYMTAB
symtab_command
struct symtab_command {
    // 共有属性。指明当前描述的加载命令，当前被设置为LC_SYMTAB
    uint32_t cmd ;
    // 共有属性。指明加载命令的大小，当前被设置为sizeof(symtab_command)
    uint32_t cmdsize;
    // 表示从文件开始到symbol table所在位置的偏移量。symbol table用[nlist]来表示
    uint32_t symoff;
    // 符号表内符号的数量
    uint32_t nsyms;
    // 表示从文件开始到string table所在位置的偏移量。
    uint32_t stroff;
    // 表示string table大小(以byteカ单位)
    uint32_t strsize;
};
搭建测试项目
#!/bin/sh

RunCommand() {

  if [[ -n "$VERBOSE_SCRIPT_LOGGING" ]]; then

      if [[ -n "$TTY" ]]; then
          echo "♦ $@" 1>$TTY
      else
          echo "♦ $*"
      fi
      echo "------------------------------------------------------------------------------" 1>$TTY
  fi

  if [[ -n "$TTY" ]]; then
        eval "$@" &>$TTY
  else
      "$@"
  fi

  return $?
}

EchoError() {

    if [[ -n "$TTY" ]]; then
        echo "$@" 1>&2>$TTY
    else
        echo "$@" 1>&2
    fi
    
}

RunCMDToTTY() {
    if [[ ! -e "$TTY" ]]; then
        EchoError "=========================================="
        EchoError "ERROR: Not Config tty to output."
        exit -1
    fi

    if [[ -n "$CMD" ]]; then
        RunCommand $CMD
    else
        EchoError "=========================================="
        EchoError "ERROR:Failed to run CMD. THE CMD must not null"
    fi
}

RunCMDToTTY
C语言符号
#import <Foundation/Foundation.h>

int global_uninit_value;

int global_init_value = 10;
double default_x __attribute__((visibility("hidden")));

static int static_init_value = 9;
static int static_uninit_value;

int main(int argc, char *argv[]) {
    static_uninit_value = 10;
    NSLog(@"%d", static_init_value);
    return 0;
}

0000000100008008 d __dyld_private
0000000100008014 d _static_init_value
0000000100008018 b _static_uninit_value
0000000100008028 s _default_x
0000000000000000 - 00 0000    SO /Users/zang/Zang/Spark/MachOAndSymbol/
0000000000000000 - 00 0000    SO main.m
0000000060335e1d - 03 0001   OSO /Users/zang/Library/Developer/Xcode/DerivedData/MachOAndSymbol-bdzlylfoorwnhggerxdmwocpeyad/Build/Intermediates.noindex/MachOAndSymbol.build/Debug/MachOAndSymbol.build/Objects-normal/x86_64/main.o
0000000100003f50 - 01 0000 BNSYM
0000000100003f50 - 01 0000   FUN _main
000000000000003f - 00 0000   FUN
000000000000003f - 01 0000 ENSYM
0000000000000000 - 00 0000  GSYM _global_init_value
0000000100008014 - 0a 0000 STSYM _static_init_value
0000000100008018 - 0b 0000 STSYM _static_uninit_value
0000000000000000 - 00 0000  GSYM _global_uninit_value
0000000000000000 - 00 0000  GSYM _default_x
0000000000000000 - 01 0000    SO
0000000100000000 T __mh_execute_header
0000000100008010 D _global_init_value
0000000100008020 S _global_uninit_value
0000000100003f50 T _main
                 U _NSLog
                 U ___CFConstantStringClassReference
                 U dyld_stub_binder

SYMBOL TABLE:
0000000100008008 l     O __DATA,__data __dyld_private
0000000100008014 l     O __DATA,__data _static_init_value
0000000100008018 l     O __DATA,__bss _static_uninit_value
0000000100008028 l     O __DATA,__common _default_x
0000000000000000 l    d  *UND* /Users/zang/Zang/Spark/study/iOS高级强化/20210118-iOS强化第二节课：符号与链接（下）/上课代码/MachOAndSymbol/
0000000000000000 l    d  *UND* main.m
0000000060335b53 l    d  *UND* /Users/zang/Library/Developer/Xcode/DerivedData/MachOAndSymbol-bdzlylfoorwnhggerxdmwocpeyad/Build/Intermediates.noindex/MachOAndSymbol.build/Debug/MachOAndSymbol.build/Objects-normal/x86_64/main.o
0000000100003f50 l    d  *UND*
0000000100003f50 l    d  *UND* _main
000000000000003f l    d  *UND*
000000000000003f l    d  *UND*
0000000000000000 l    d  *UND* _global_init_value
0000000100008014 l    d  *UND* _static_init_value
0000000100008018 l    d  *UND* _static_uninit_value
0000000000000000 l    d  *UND* _global_uninit_value
0000000000000000 l    d  *UND* _default_x
0000000000000000 l    d  *UND*
0000000100000000 g     F __TEXT,__text __mh_execute_header
0000000100008010 g     O __DATA,__data _global_init_value
0000000100008020 g     O __DATA,__common _global_uninit_value
0000000100003f50 g     F __TEXT,__text _main
0000000000000000         *UND* _NSLog
0000000000000000         *UND* ___CFConstantStringClassReference
0000000000000000         *UND* dyld_stub_binder
剥离调试符号

调试符号：当文件编译成.o文件时，它会生成DWARF格式的调试信息，放在__DWARF段。链接时，将__DWARF段变成符号放到符号表中。

上面的打印信息中，包含大量调试符号。为了避免干扰，下面介绍如何剥离调试符号。

符号可见性

全局符号和本地符号，它们本质上的区别就是可见性

导入符号和导出符号
#import "LGOneObject.h"

@interface LGOneObject : NSObject

- (void)testOneObject;

@end

@implementation LGOneObject

- (void)testOneObject {
    NSLog(@"testOneObject");
}

@end
Weak Symbol
Common Symbol
重新导出符号
图解
查看项目使用的三方库和符号等信息
# Path: /Users/zang/Library/Developer/Xcode/DerivedData/MachOAndSymbol-bdzlylfoorwnhggerxdmwocpeyad/Build/Products/Debug/MachOAndSymbol
# Arch: x86_64
# Object files:
[  0] linker synthesized
[  1] /Users/zang/Library/Developer/Xcode/DerivedData/MachOAndSymbol-bdzlylfoorwnhggerxdmwocpeyad/Build/Intermediates.noindex/MachOAndSymbol.build/Debug/MachOAndSymbol.build/Objects-normal/x86_64/LGOneObject.o
[  2] /Users/zang/Library/Developer/Xcode/DerivedData/MachOAndSymbol-bdzlylfoorwnhggerxdmwocpeyad/Build/Intermediates.noindex/MachOAndSymbol.build/Debug/MachOAndSymbol.build/Objects-normal/x86_64/main.o
[  3] /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.1.sdk/System/Library/Frameworks//Foundation.framework/Foundation.tbd
# Sections:
# Address   Size        Segment Section
0x100003EF0 0x0000006F  __TEXT  __text
0x100003F60 0x00000006  __TEXT  __stubs
0x100003F68 0x0000001A  __TEXT  __stub_helper
0x100003F82 0x00000011  __TEXT  __cstring
0x100003F93 0x0000000C  __TEXT  __objc_classname
0x100003F9F 0x0000000E  __TEXT  __objc_methname
0x100003FAD 0x00000008  __TEXT  __objc_methtype
0x100003FB8 0x00000048  __TEXT  __unwind_info
0x100004000 0x00000008  __DATA_CONST    __got
0x100004008 0x00000040  __DATA_CONST    __cfstring
0x100004048 0x00000008  __DATA_CONST    __objc_classlist
0x100004050 0x00000008  __DATA_CONST    __objc_imageinfo
0x100008000 0x00000008  __DATA  __la_symbol_ptr
0x100008008 0x000000B0  __DATA  __objc_const
0x1000080B8 0x00000050  __DATA  __objc_data
0x100008108 0x00000010  __DATA  __data
0x100008118 0x00000004  __DATA  __bss
0x100008120 0x00000010  __DATA  __common
# Symbols:
# Address   Size        File  Name
0x100003EF0 0x00000027  [  1] -[LGOneObject testOneObject]
0x100003F20 0x0000003F  [  2] _main
0x100003F60 0x00000006  [  3] _NSLog
0x100003F68 0x00000010  [  0] helper helper
0x100003F78 0x0000000A  [  3] _NSLog
0x100003F82 0x0000000E  [  1] literal string: testOneObject
0x100003F90 0x00000003  [  2] literal string: %d
0x100003F93 0x0000000C  [  1] literal string: LGOneObject
0x100003F9F 0x0000000E  [  1] literal string: testOneObject
0x100003FAD 0x00000008  [  1] literal string: v16@0:8
0x100003FB8 0x00000048  [  0] compact unwind info
0x100004000 0x00000008  [  0] non-lazy-pointer-to-local: dyld_stub_binder
0x100004008 0x00000020  [  1] CFString
0x100004028 0x00000020  [  2] CFString
0x100004048 0x00000008  [  1] objc-cat-list
0x100004050 0x00000008  [  0] objc image info
0x100008000 0x00000008  [  3] _NSLog
0x100008008 0x00000048  [  1] __OBJC_METACLASS_RO_$_LGOneObject
0x100008050 0x00000020  [  1] __OBJC_$_INSTANCE_METHODS_LGOneObject
0x100008070 0x00000048  [  1] __OBJC_CLASS_RO_$_LGOneObject
0x1000080B8 0x00000028  [  1] _OBJC_METACLASS_$_LGOneObject
0x1000080E0 0x00000028  [  1] _OBJC_CLASS_$_LGOneObject
0x100008108 0x00000008  [  0] __dyld_private
0x100008110 0x00000004  [  2] _global_init_value
0x100008114 0x00000004  [  2] _static_init_value
0x100008118 0x00000004  [  2] _static_uninit_value
0x100008120 0x00000008  [  2] _global_uninit_value
0x100008128 0x00000008  [  2] _default_x
Section的名称与作用
名称 作用
TEXT.text 可执行的机器码
TEXT.cstring 去重后的C字符串
TEXT.const 初始化过的常量
TEXT.stubs 符号桩。lazybinding的表对 应项指针指向的地址的代码
TEXT.stub_ helper 辅助函数。当在lazybinding的表中没有找到对应项的指针表示的真正的符号地址的时候，指向这
TEXT.unwind_info 存储处理异常情况信息
TEXT.eh_frame 调试辅助信息
DATA.data 初始化过的可变的数据
DATA.nI_symbol_ptr 非lazy-binding的指针表，每个表中的指针指向一个在装载过程中，被动态链接器搜索完成的符号
DATA.Ia_symbol_ptr lazy-binding的指针表，每个表中的指针一开始指向stub_helper
DATA.const 没有初始化过的常量
DATA.mod_init_func 初始化函数，在main之前调用
DATA.mod_term_func 终止函数，在main返回之后调用
DATA.bss 没有初始化的静态变量
DATA.common 没有初始化过的符号声明（for example, int I;）
Swift符号表
0000000100003f8a lw    O __TEXT,__swift5_typeref _symbolic _____ 14MachOAndSymbol012LGSwiftClassC0C
0000000100003f90 l     O __TEXT,__swift5_fieldmd _$s14MachOAndSymbol012LGSwiftClassC0CMF
0000000100008020 l     O __DATA,__objc_const __METACLASS_DATA__TtC14MachOAndSymbol18LGSwiftClassSymbol
0000000100008068 l     O __DATA,__objc_const __DATA__TtC14MachOAndSymbol18LGSwiftClassSymbol
00000001000080e8 l     O __DATA,__data _$s14MachOAndSymbol012LGSwiftClassC0CMf
0000000100003d90 g     F __TEXT,__text _$s14MachOAndSymbol012LGSwiftClassC0C09testSwiftC0yyF
0000000100003f78 g     O __TEXT,__const _$s14MachOAndSymbol012LGSwiftClassC0C09testSwiftC0yyFTq
0000000100003e10 g     F __TEXT,__text _$s14MachOAndSymbol012LGSwiftClassC0CACycfC
0000000100003f80 g     O __TEXT,__const _$s14MachOAndSymbol012LGSwiftClassC0CACycfCTq
0000000100003e40 g     F __TEXT,__text _$s14MachOAndSymbol012LGSwiftClassC0CACycfc
0000000100003e60 g     F __TEXT,__text _$s14MachOAndSymbol012LGSwiftClassC0CMa
00000001000080c0 g     O __DATA,__data _$s14MachOAndSymbol012LGSwiftClassC0CMm
0000000100003f44 g     O __TEXT,__const _$s14MachOAndSymbol012LGSwiftClassC0CMn
00000001000080f8 g     O __DATA,__data _$s14MachOAndSymbol012LGSwiftClassC0CN
0000000100003dd0 g     F __TEXT,__text _$s14MachOAndSymbol012LGSwiftClassC0CfD
0000000100003db0 g     F __TEXT,__text _$s14MachOAndSymbol012LGSwiftClassC0Cfd
0000000000000000         *UND* _OBJC_CLASS_$__TtCs12_SwiftObject
0000000000000000         *UND* _OBJC_METACLASS_$__TtCs12_SwiftObject

0000000100003d10 l     F __TEXT,__text _$s14MachOAndSymbol012LGSwiftClassC033_66093EBE10D00815F1A5CBD65FFF4661LLC09testSwiftC0yyF
0000000100003d30 l     F __TEXT,__text _$s14MachOAndSymbol012LGSwiftClassC033_66093EBE10D00815F1A5CBD65FFF4661LLCfd
0000000100003d50 l     F __TEXT,__text _$s14MachOAndSymbol012LGSwiftClassC033_66093EBE10D00815F1A5CBD65FFF4661LLCfD
0000000100003d90 l     F __TEXT,__text _$s14MachOAndSymbol012LGSwiftClassC033_66093EBE10D00815F1A5CBD65FFF4661LLCMa
0000000100003db0 l     F __TEXT,__text _$s14MachOAndSymbol012LGSwiftClassC033_66093EBE10D00815F1A5CBD65FFF4661LLCADycfC
0000000100003de0 l     F __TEXT,__text _$s14MachOAndSymbol012LGSwiftClassC033_66093EBE10D00815F1A5CBD65FFF4661LLCADycfc
0000000100003f1c lw    O __TEXT,__const _$s14MachOAndSymbol012LGSwiftClassC033_66093EBE10D00815F1A5CBD65FFF4661LLCMXX
0000000100003f44 l     O __TEXT,__const _$s14MachOAndSymbol012LGSwiftClassC033_66093EBE10D00815F1A5CBD65FFF4661LLCMn
0000000100003f78 l     O __TEXT,__const _$s14MachOAndSymbol012LGSwiftClassC033_66093EBE10D00815F1A5CBD65FFF4661LLC09testSwiftC0yyFTq
0000000100003f80 l     O __TEXT,__const _$s14MachOAndSymbol012LGSwiftClassC033_66093EBE10D00815F1A5CBD65FFF4661LLCADycfCTq
0000000100003f8a lw    O __TEXT,__swift5_typeref _symbolic _____ 14MachOAndSymbol012LGSwiftClassC033_66093EBE10D00815F1A5CBD65FFF4661LLC
0000000100003f90 l     O __TEXT,__swift5_fieldmd _$s14MachOAndSymbol012LGSwiftClassC033_66093EBE10D00815F1A5CBD65FFF4661LLCMF
0000000100008020 l     O __DATA,__objc_const __METACLASS_DATA__TtC14MachOAndSymbolP33_66093EBE10D00815F1A5CBD65FFF466118LGSwiftClassSymbol
0000000100008068 l     O __DATA,__objc_const __DATA__TtC14MachOAndSymbolP33_66093EBE10D00815F1A5CBD65FFF466118LGSwiftClassSymbol
00000001000080c0 l     O __DATA,__data _$s14MachOAndSymbol012LGSwiftClassC033_66093EBE10D00815F1A5CBD65FFF4661LLCMm
00000001000080e8 l     O __DATA,__data _$s14MachOAndSymbol012LGSwiftClassC033_66093EBE10D00815F1A5CBD65FFF4661LLCMf
00000001000080f8 l     O __DATA,__data _$s14MachOAndSymbol012LGSwiftClassC033_66093EBE10D00815F1A5CBD65FFF4661LLCN
0000000000000000         *UND* _OBJC_CLASS_$__TtCs12_SwiftObject
0000000000000000         *UND* _OBJC_METACLASS_$__TtCs12_SwiftObject
$(SRCROOT)和$(PROJECT_DIR)的区别
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