linker load elf (2)
// SimpleSection.o 0000000: 7f45 4c46 0201 0100 0000 0000 0000 0000 .ELF............ 0000010: 0100 3e00 0100 0000 0000 0000 0000 0000 ..>............. 0000020: 0000 0000 0000 0000 9001 0000 0000 0000 ................ 0000030: 0000 0000 4000 0000 0000 4000 0d00 0a00 ....@.....@..... 0000040: 5548 89e5 4883 ec10 897d fcb8 0000 0000 UH..H....}...... 0000050: 8b55 fc89 d648 89c7 b800 0000 00e8 0000 .U...H.......... 0000060: 0000 c9c3 5548 89e5 4883 ec10 c745 f801 ....UH..H....E.. 0000070: 0000 008b 1500 0000 008b 0500 0000 0001 ................ 0000080: d003 45f8 0345 fc89 c7e8 0000 0000 8b45 ..E..E.........E 0000090: f8c9 c300 5400 0000 5500 0000 2564 0a00 ....T...U...%d.. 00000a0: 0047 4343 3a20 2855 6275 6e74 752f 4c69 .GCC: (Ubuntu/Li 00000b0: 6e61 726f 2034 2e36 2e33 2d31 7562 756e naro 4.6.3-1ubun 00000c0: 7475 3529 2034 2e36 2e33 0000 0000 0000 tu5) 4.6.3...... 00000d0: 1400 0000 0000 0000 017a 5200 0178 1001 .........zR..x.. 00000e0: 1b0c 0708 9001 0000 1c00 0000 1c00 0000 ................ 00000f0: 0000 0000 2400 0000 0041 0e10 8602 430d ....$....A....C. 0000100: 065f 0c07 0800 0000 1c00 0000 3c00 0000 ._..........<... 0000110: 0000 0000 2f00 0000 0041 0e10 8602 430d ..../....A....C. 0000120: 066a 0c07 0800 0000 002e 7379 6d74 6162 .j........symtab 0000130: 002e 7374 7274 6162 002e 7368 7374 7274 ..strtab..shstrt 0000140: 6162 002e 7265 6c61 2e74 6578 7400 2e64 ab..rela.text..d 0000150: 6174 6100 2e62 7373 002e 726f 6461 7461 ata..bss..rodata 0000160: 002e 636f 6d6d 656e 7400 2e6e 6f74 652e ..comment..note. 0000170: 474e 552d 7374 6163 6b00 2e72 656c 612e GNU-stack..rela. 0000180: 6568 5f66 7261 6d65 0000 0000 0000 0000 eh_frame........ 0000190: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 00001a0: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 00001b0: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 00001c0: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 00001d0: 2000 0000 0100 0000 0600 0000 0000 0000 ............... 00001e0: 0000 0000 0000 0000 4000 0000 0000 0000 ........@....... 00001f0: 5300 0000 0000 0000 0000 0000 0000 0000 S............... 0000200: 0400 0000 0000 0000 0000 0000 0000 0000 ................ 0000210: 1b00 0000 0400 0000 0000 0000 0000 0000 ................ 0000220: 0000 0000 0000 0000 b806 0000 0000 0000 ................ 0000230: 7800 0000 0000 0000 0b00 0000 0100 0000 x............... 0000240: 0800 0000 0000 0000 1800 0000 0000 0000 ................ 0000250: 2600 0000 0100 0000 0300 0000 0000 0000 &............... 0000260: 0000 0000 0000 0000 9400 0000 0000 0000 ................ 0000270: 0800 0000 0000 0000 0000 0000 0000 0000 ................ 0000280: 0400 0000 0000 0000 0000 0000 0000 0000 ................ 0000290: 2c00 0000 0800 0000 0300 0000 0000 0000 ,............... 00002a0: 0000 0000 0000 0000 9c00 0000 0000 0000 ................ 00002b0: 0400 0000 0000 0000 0000 0000 0000 0000 ................ 00002c0: 0400 0000 0000 0000 0000 0000 0000 0000 ................ 00002d0: 3100 0000 0100 0000 0200 0000 0000 0000 1............... 00002e0: 0000 0000 0000 0000 9c00 0000 0000 0000 ................ 00002f0: 0400 0000 0000 0000 0000 0000 0000 0000 ................ 0000300: 0100 0000 0000 0000 0000 0000 0000 0000 ................ 0000310: 3900 0000 0100 0000 3000 0000 0000 0000 9.......0....... 0000320: 0000 0000 0000 0000 a000 0000 0000 0000 ................ 0000330: 2b00 0000 0000 0000 0000 0000 0000 0000 +............... 0000340: 0100 0000 0000 0000 0100 0000 0000 0000 ................ 0000350: 4200 0000 0100 0000 0000 0000 0000 0000 B............... 0000360: 0000 0000 0000 0000 cb00 0000 0000 0000 ................ 0000370: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 0000380: 0100 0000 0000 0000 0000 0000 0000 0000 ................ 0000390: 5700 0000 0100 0000 0200 0000 0000 0000 W............... 00003a0: 0000 0000 0000 0000 d000 0000 0000 0000 ................ 00003b0: 5800 0000 0000 0000 0000 0000 0000 0000 X............... 00003c0: 0800 0000 0000 0000 0000 0000 0000 0000 ................ 00003d0: 5200 0000 0400 0000 0000 0000 0000 0000 R............... 00003e0: 0000 0000 0000 0000 3007 0000 0000 0000 ........0....... 00003f0: 3000 0000 0000 0000 0b00 0000 0800 0000 0............... 0000400: 0800 0000 0000 0000 1800 0000 0000 0000 ................ 0000410: 1100 0000 0300 0000 0000 0000 0000 0000 ................ 0000420: 0000 0000 0000 0000 2801 0000 0000 0000 ........(....... 0000430: 6100 0000 0000 0000 0000 0000 0000 0000 a............... 0000440: 0100 0000 0000 0000 0000 0000 0000 0000 ................ 0000450: 0100 0000 0200 0000 0000 0000 0000 0000 ................ 0000460: 0000 0000 0000 0000 d004 0000 0000 0000 ................ 0000470: 8001 0000 0000 0000 0c00 0000 0b00 0000 ................ 0000480: 0800 0000 0000 0000 1800 0000 0000 0000 ................ 0000490: 0900 0000 0300 0000 0000 0000 0000 0000 ................ 00004a0: 0000 0000 0000 0000 5006 0000 0000 0000 ........P....... 00004b0: 6600 0000 0000 0000 0000 0000 0000 0000 f............... 00004c0: 0100 0000 0000 0000 0000 0000 0000 0000 ................ 00004d0: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 00004e0: 0000 0000 0000 0000 0100 0000 0400 f1ff ................ 00004f0: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 0000500: 0000 0000 0300 0100 0000 0000 0000 0000 ................ 0000510: 0000 0000 0000 0000 0000 0000 0300 0300 ................ 0000520: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 0000530: 0000 0000 0300 0400 0000 0000 0000 0000 ................ 0000540: 0000 0000 0000 0000 0000 0000 0300 0500 ................ 0000550: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 0000560: 1100 0000 0100 0300 0400 0000 0000 0000 ................ 0000570: 0400 0000 0000 0000 2100 0000 0100 0400 ........!....... 0000580: 0000 0000 0000 0000 0400 0000 0000 0000 ................ 0000590: 0000 0000 0300 0700 0000 0000 0000 0000 ................ 00005a0: 0000 0000 0000 0000 0000 0000 0300 0800 ................ 00005b0: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 00005c0: 0000 0000 0300 0600 0000 0000 0000 0000 ................ 00005d0: 0000 0000 0000 0000 3200 0000 1100 0300 ........2....... 00005e0: 0000 0000 0000 0000 0400 0000 0000 0000 ................ 00005f0: 4200 0000 1100 f2ff 0400 0000 0000 0000 B............... 0000600: 0400 0000 0000 0000 5400 0000 1200 0100 ........T....... 0000610: 0000 0000 0000 0000 2400 0000 0000 0000 ........$....... 0000620: 5a00 0000 1000 0000 0000 0000 0000 0000 Z............... 0000630: 0000 0000 0000 0000 6100 0000 1200 0100 ........a....... 0000640: 2400 0000 0000 0000 2f00 0000 0000 0000 $......./....... 0000650: 0053 696d 706c 6553 6563 7469 6f6e 2e63 .SimpleSection.c 0000660: 0073 7461 7469 635f 7661 722e 3230 3439 .static_var.2049 0000670: 0073 7461 7469 635f 7661 7232 2e32 3035 .static_var2.205 0000680: 3000 676c 6f62 616c 5f69 6e69 745f 7661 0.global_init_va 0000690: 7200 676c 6f62 616c 5f75 6e69 6e69 745f r.global_uninit_ 00006a0: 7661 7200 6675 6e63 3100 7072 696e 7466 var.func1.printf 00006b0: 006d 6169 6e00 0000 0c00 0000 0000 0000 .main........... 00006c0: 0a00 0000 0500 0000 0000 0000 0000 0000 ................ 00006d0: 1e00 0000 0000 0000 0200 0000 0e00 0000 ................ 00006e0: fcff ffff ffff ffff 3500 0000 0000 0000 ........5....... 00006f0: 0200 0000 0300 0000 0000 0000 0000 0000 ................ 0000700: 3b00 0000 0000 0000 0200 0000 0400 0000 ;............... 0000710: fcff ffff ffff ffff 4a00 0000 0000 0000 ........J....... 0000720: 0200 0000 0d00 0000 fcff ffff ffff ffff ................ 0000730: 2000 0000 0000 0000 0200 0000 0200 0000 ............... 0000740: 0000 0000 0000 0000 4000 0000 0000 0000 ........@....... 0000750: 0200 0000 0200 0000 2400 0000 0000 0000 ........$....... 0000760: 0a .
Elf64_Ehdr描述elf header
typedef struct { unsigned char e_ident[EI_NIDENT]; /* 16 Magic number and other info */ Elf64_Half e_type; /* 2 Object file type */ Elf64_Half e_machine; /* 2 Architecture */ Elf64_Word e_version; /* 4 Object file version */ Elf64_Addr e_entry; /* 8 Entry point virtual address */ Elf64_Off e_phoff; /* 8 Program header table file offset */ Elf64_Off e_shoff; /* 8 Section header table file offset */ section table offset address Elf64_Word e_flags; /* 4 Processor-specific flags */ Elf64_Half e_ehsize; /* 2 ELF header size in bytes */ 段描述符的大小，也就是sizeof(Elf64_Ehdr) = 64 Elf64_Half e_phentsize; /* 2 Program header table entry size */ Elf64_Half e_phnum; /* 2 Program header table entry count */ Elf64_Half e_shentsize; /* 2 Section header table entry size */ Elf64_Half e_shnum; /* 2 Section header table entry count */ 段的个数 Elf64_Half e_shstrndx; /* 2 Section header string table index */ } Elf64_Ehdr;
0000000: 7f45 4c46 0201 0100 0000 0000 0000 0000 .ELF............
0000010: 0100 3e00 0100 0000 0000 0000 0000 0000 ..>.............
0000020: 0000 0000 0000 0000 9001 0000 0000 0000 ................
0000030: 0000 0000 4000 0000 0000 4000 0d00 0a00 ....@.....@.....
Elf64_Off e_shoff = 0x0000000000000190 = 400
也就是说section table offset = 0x190 = 400
段的个数为0x000d = 13 e_shstrndx = 0x000a = 10 表示段表字符串在第10个段中
-----------------------
| ELF Header | e_shoff----
----------------------- | 0x190 = 400
| .text | |
----------------------- |
| .data | |
----------------------- |
| .bss | |
----------------------- |
| .rodata | |
----------------------- |
| . comment | |
----------------------- |
| .other sections. | |
-----------------------<-----------
| Section table |
-----------------------
| String Tables |
-----------------------
| Symbol Tables |
-----------------------
| .............. |
-----------------------
// 段表有很多个段描述，段描述的数据结构为Elf64_Shdr
typedef struct { Elf64_Word sh_name; /* 4 Section name (string tbl index) */ Elf64_Word sh_type; /* 4 Section type */ Elf64_Xword sh_flags; /* 8 Section flags */ Elf64_Addr sh_addr; /* 8 Section virtual addr at execution */ Elf64_Off sh_offset; /* 8 Section file offset */ Elf64_Xword sh_size; /* 8 Section size in bytes */ Elf64_Word sh_link; /* 4 Link to another section */ Elf64_Word sh_info; /* 4 Additional section information */ Elf64_Xword sh_addralign; /* 8 Section alignment */ Elf64_Xword sh_entsize; /* 8 Entry size if section holds table */ } Elf64_Shdr;
mutian@mutian:~/share/test$ readelf -S SimpleSection.o There are 13 section headers, starting at offset 0x190: Section Headers: [Nr] Name Type Address Offset Size EntSize Flags Link Info Align [ 0] NULL 0000000000000000 00000000 0000000000000000 0000000000000000 0 0 0 [ 1] .text PROGBITS 0000000000000000 00000040 0000000000000053 0000000000000000 AX 0 0 4 [ 2] .rela.text RELA 0000000000000000 000006b8 0000000000000078 0000000000000018 11 1 8 [ 3] .data PROGBITS 0000000000000000 00000094 0000000000000008 0000000000000000 WA 0 0 4 [ 4] .bss NOBITS 0000000000000000 0000009c 0000000000000004 0000000000000000 WA 0 0 4 [ 5] .rodata PROGBITS 0000000000000000 0000009c 0000000000000004 0000000000000000 A 0 0 1 [ 6] .comment PROGBITS 0000000000000000 000000a0 000000000000002b 0000000000000001 MS 0 0 1 [ 7] .note.GNU-stack PROGBITS 0000000000000000 000000cb 0000000000000000 0000000000000000 0 0 1 [ 8] .eh_frame PROGBITS 0000000000000000 000000d0 0000000000000058 0000000000000000 A 0 0 8 [ 9] .rela.eh_frame RELA 0000000000000000 00000730 0000000000000030 0000000000000018 11 8 8 [10] .shstrtab STRTAB 0000000000000000 00000128 0000000000000061 0000000000000000 0 0 1 [11] .symtab SYMTAB 0000000000000000 000004d0 0000000000000180 0000000000000018 12 11 8 [12] .strtab STRTAB 0000000000000000 00000650 0000000000000066 0000000000000000 0 0 1
// 第一段是无效的段 0000190: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 00001a0: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 00001b0: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 00001c0: 0000 0000 0000 0000 0000 0000 0000 0000 ................ // 第二段 00001d0: 2000 0000 0100 0000 0600 0000 0000 0000 ............... 00001e0: 0000 0000 0000 0000 4000 0000 0000 0000 ........@....... 00001f0: 5300 0000 0000 0000 0000 0000 0000 0000 S............... 0000200: 0400 0000 0000 0000 0000 0000 0000 0000 ................ // sh_name = 0x20 sh_type = 0x1 sh_flags = 0x6 偏移地址sh_offset = 0x40
// sh_size = 0x53 sh_addralign = 0x04 按4字节对齐 // 第三段 0000210: 1b00 0000 0400 0000 0000 0000 0000 0000 ................ 0000220: 0000 0000 0000 0000 b806 0000 0000 0000 ................ 0000230: 7800 0000 0000 0000 0b00 0000 0100 0000 x............... 0000240: 0800 0000 0000 0000 1800 0000 0000 0000 ................ // 偏移地址sh_offset = 0x6b8 sh_size = 0x78 // 第四段 0000250: 2600 0000 0100 0000 0300 0000 0000 0000 &............... 0000260: 0000 0000 0000 0000 9400 0000 0000 0000 ................ 0000270: 0800 0000 0000 0000 0000 0000 0000 0000 ................ 0000280: 0400 0000 0000 0000 0000 0000 0000 0000 ................ // 偏移地址sh_offset = 0x94 sh_size = 0x8 ...........................................
/* Legal values for sh_type (section type). */ #define SHT_NULL 0 /* Section header table entry unused */ #define SHT_PROGBITS 1 /* Program data */ #define SHT_SYMTAB 2 /* Symbol table */ #define SHT_STRTAB 3 /* String table */ #define SHT_RELA 4 /* Relocation entries with addends */ #define SHT_HASH 5 /* Symbol hash table */ #define SHT_DYNAMIC 6 /* Dynamic linking information */ #define SHT_NOTE 7 /* Notes */ #define SHT_NOBITS 8 /* Program space with no data (bss) */ #define SHT_REL 9 /* Relocation entries, no addends */ #define SHT_SHLIB 10 /* Reserved */ #define SHT_DYNSYM 11 /* Dynamic linker symbol table */ #define SHT_INIT_ARRAY 14 /* Array of constructors */ #define SHT_FINI_ARRAY 15 /* Array of destructors */ #define SHT_PREINIT_ARRAY 16 /* Array of pre-constructors */ #define SHT_GROUP 17 /* Section group */ #define SHT_SYMTAB_SHNDX 18 /* Extended section indeces */ #define SHT_NUM 19 /* Number of defined types. */ #define SHT_LOOS 0x60000000 /* Start OS-specific. */ #define SHT_GNU_ATTRIBUTES 0x6ffffff5 /* Object attributes. */ #define SHT_GNU_HASH 0x6ffffff6 /* GNU-style hash table. */ #define SHT_GNU_LIBLIST 0x6ffffff7 /* Prelink library list */ #define SHT_CHECKSUM 0x6ffffff8 /* Checksum for DSO content. */ #define SHT_LOSUNW 0x6ffffffa /* Sun-specific low bound. */ #define SHT_SUNW_move 0x6ffffffa #define SHT_SUNW_COMDAT 0x6ffffffb #define SHT_SUNW_syminfo 0x6ffffffc #define SHT_GNU_verdef 0x6ffffffd /* Version definition section. */ #define SHT_GNU_verneed 0x6ffffffe /* Version needs section. */ #define SHT_GNU_versym 0x6fffffff /* Version symbol table. */ #define SHT_HISUNW 0x6fffffff /* Sun-specific high bound. */ #define SHT_HIOS 0x6fffffff /* End OS-specific type */ #define SHT_LOPROC 0x70000000 /* Start of processor-specific */ #define SHT_HIPROC 0x7fffffff /* End of processor-specific */ #define SHT_LOUSER 0x80000000 /* Start of application-specific */ #define SHT_HIUSER 0x8fffffff /* End of application-specific */ /* Legal values for sh_flags (section flags). */ #define SHF_WRITE (1 << 0) /* Writable */ #define SHF_ALLOC (1 << 1) /* Occupies memory during execution */ #define SHF_EXECINSTR (1 << 2) /* Executable */ #define SHF_MERGE (1 << 4) /* Might be merged */ #define SHF_STRINGS (1 << 5) /* Contains nul-terminated strings */ #define SHF_INFO_LINK (1 << 6) /* `sh_info' contains SHT index */ #define SHF_LINK_ORDER (1 << 7) /* Preserve order after combining */ #define SHF_OS_NONCONFORMING (1 << 8) /* Non-standard OS specific handling required */ #define SHF_GROUP (1 << 9) /* Section is member of a group. */ #define SHF_TLS (1 << 10) /* Section hold thread-local data. */ #define SHF_MASKOS 0x0ff00000 /* OS-specific. */ #define SHF_MASKPROC 0xf0000000 /* Processor-specific */ #define SHF_ORDERED (1 << 30) /* Special ordering requirement (Solaris). */ #define SHF_EXCLUDE (1 << 31) /* Section is excluded unless referenced or allocated (Solaris).*/
.shstrtab段包含的是段表需要的字符串，分析.shstrtab段的内容
0000120: 002e 7379 6d74 6162 ..symtab 0000130: 002e 7374 7274 6162 002e 7368 7374 7274 ..strtab..shstrt 0000140: 6162 002e 7265 6c61 2e74 6578 7400 2e64 ab..rela.text..d 0000150: 6174 6100 2e62 7373 002e 726f 6461 7461 ata..bss..rodata 0000160: 002e 636f 6d6d 656e 7400 2e6e 6f74 652e ..comment..note. 0000170: 474e 552d 7374 6163 6b00 2e72 656c 612e GNU-stack..rela. 0000180: 6568 5f66 7261 6d65 00 eh_frame........
以002e开始一个字符串，取字符串的时候只需要知道字符串在该表中的偏移地址即可。
mutian@mutian:~/share/test$ readelf -x .shstrtab SimpleSection.o Hex dump of section '.shstrtab': 0x00000000 002e7379 6d746162 002e7374 72746162 ..symtab..strtab 0x00000010 002e7368 73747274 6162002e 72656c61 ..shstrtab..rela 0x00000020 2e746578 74002e64 61746100 2e627373 .text..data..bss 0x00000030 002e726f 64617461 002e636f 6d6d656e ..rodata..commen 0x00000040 74002e6e 6f74652e 474e552d 73746163 t..note.GNU-stac 0x00000050 6b002e72 656c612e 65685f66 72616d65 k..rela.eh_frame 0x00000060 00
每个目标文件都会有一个符号表(Symbol Table)， 也就是.strtab段
.strtab段记录的是符号名，也就是变量名和函数名的字符串。每个定义的符号都有一个符号值(Symbol Value)，也就是变量或者函数的地址。如果这个符号在本源文件中没有找到，那么称这个符号为外部符号(External symbol)
0000650: 0053 696d 706c 6553 6563 7469 6f6e 2e63 .SimpleSection.c 0000660: 0073 7461 7469 635f 7661 722e 3230 3439 .static_var.2049 0000670: 0073 7461 7469 635f 7661 7232 2e32 3035 .static_var2.205 0000680: 3000 676c 6f62 616c 5f69 6e69 745f 7661 0.global_init_va 0000690: 7200 676c 6f62 616c 5f75 6e69 6e69 745f r.global_uninit_ 00006a0: 7661 7200 6675 6e63 3100 7072 696e 7466 var.func1.printf 00006b0: 006d 6169 6e00 .main.
.symtab
/* Type for section indices, which are 16-bit quantities. */ typedef uint16_t Elf32_Section; typedef uint16_t Elf64_Section; /* Symbol table entry. */ typedef struct { Elf32_Word st_name; /* Symbol name (string tbl index) */ Elf32_Addr st_value; /* Symbol value */ Elf32_Word st_size; /* Symbol size */ unsigned char st_info; /* Symbol type and binding */ unsigned char st_other; /* Symbol visibility */ Elf32_Section st_shndx; /* Section index */ } Elf32_Sym; typedef struct { Elf64_Word st_name; /* 4 Symbol name (string tbl index) */ unsigned char st_info; /* 1 Symbol type and binding */ unsigned char st_other; /* 1 Symbol visibility */ Elf64_Section st_shndx; /* 2 Section index */ Elf64_Addr st_value; /* 8 Symbol value */ Elf64_Xword st_size; /* 8 Symbol size */ } Elf64_Sym;
mutian@mutian:~/share/test$ readelf -s SimpleSection.o Symbol table '.symtab' contains 16 entries: Num: Value Size Type Bind Vis Ndx Name 0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND 1: 0000000000000000 0 FILE LOCAL DEFAULT ABS SimpleSection.c 2: 0000000000000000 0 SECTION LOCAL DEFAULT 1 3: 0000000000000000 0 SECTION LOCAL DEFAULT 3 4: 0000000000000000 0 SECTION LOCAL DEFAULT 4 5: 0000000000000000 0 SECTION LOCAL DEFAULT 5 6: 0000000000000004 4 OBJECT LOCAL DEFAULT 3 static_var.2049 7: 0000000000000000 4 OBJECT LOCAL DEFAULT 4 static_var2.2050 8: 0000000000000000 0 SECTION LOCAL DEFAULT 7 9: 0000000000000000 0 SECTION LOCAL DEFAULT 8 10: 0000000000000000 0 SECTION LOCAL DEFAULT 6 11: 0000000000000000 4 OBJECT GLOBAL DEFAULT 3 global_init_var 12: 0000000000000004 4 OBJECT GLOBAL DEFAULT COM global_uninit_var 13: 0000000000000000 36 FUNC GLOBAL DEFAULT 1 func1 14: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND printf 15: 0000000000000024 47 FUNC GLOBAL DEFAULT 1 main
每一个符号用24个字节表示，第一个字节是无效的字节。
00004d0: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 00004e0: 0000 0000 0000 0000 0100 0000 0400 f1ff ................ 00004f0: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 0000500: 0000 0000 0300 0100 0000 0000 0000 0000 ................ 0000510: 0000 0000 0000 0000 0000 0000 0300 0300 ................ 0000520: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 0000530: 0000 0000 0300 0400 0000 0000 0000 0000 ................ 0000540: 0000 0000 0000 0000 0000 0000 0300 0500 ................ 0000550: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 0000560: 1100 0000 0100 0300 0400 0000 0000 0000 ................ 0000570: 0400 0000 0000 0000 2100 0000 0100 0400 ........!....... 0000580: 0000 0000 0000 0000 0400 0000 0000 0000 ................ ..............
ELF是采用一个叫DWARF(Debug with Arbitrary Record Format)的标准的调试信息格式。
MicroSoft也有自己相应的调试信息格式标准，叫Code View
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