一，简介
本文主要介绍什么是elf文件，以及查看elf文件内部信息的常用命令。
二，ELF文件介绍
ELF（Excutable Linkable Format）。
ELF文件不仅包括可执行文件还包括动态链接库和静态链接库。
三，常用命令汇总
objdump:
| 命令 | 功能介绍 |
|---|---|
| objdump -h SimpleSection.o | 打印elf文件各段的基本信息 |
| objdump -x SimpleSection.o | 把elf文件更多的信息打印出来 |
| size SimpleSection.o | 查看代码段，数据段，bss段长度 |
| objdump -s -d SimpleSection.o | 分析代码段的内容。-s 把所有参数以16进制打印出来，-d 所有包含指令的段反汇编 |
| objdump -r SimpleSection.o | 查看elf文件中要重定位的地方，即elf文件中所有引用到外部符号的地址 |
readelf：
| 命令 | 功能介绍 |
|---|---|
| readelf -h SimpleSection.o | 查看elf文件头 |
| readelf -S SimpleSection.o | 查看elf文件段，它显示的结果才是真正的段表结构 |
| readelf -s SimpleSection.o | 查看elf文件的符号 |
| readelf -h SimpleSection.o | 查看elf文件头 |
nm：
| 命令 | 功能介绍 |
|---|---|
| nm SimpleSection.o | 查看elf符号表 |
四，命令使用示例
本章节以SimpleSection.c为例，在linux环境下执行常用命令查看效果。
SimpleSection.c：
int printf(const char *format, ...);
int global_init_var = 84;
int global_uninit_var;
void func1(int i)
{
printf("%d\n", i);
}
int main()
{
static int static_var = 85;
static int static_var2;
int a = 1;
int b;
func1(static_var + static_var2 + a + b);
return a;
}
使用gcc命令编译成.o文件：
gcc -c SimpleSection.c
4.1 objdump -h SimpleSection.o
objdump -h SimpleSection.o
SimpleSection.o: file format elf64-x86-64
Sections:
Idx Name Size VMA LMA File off Algn
0 .text 00000055 0000000000000000 0000000000000000 00000040 2**0
CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
1 .data 00000008 0000000000000000 0000000000000000 00000098 2**2
CONTENTS, ALLOC, LOAD, DATA
2 .bss 00000004 0000000000000000 0000000000000000 000000a0 2**2
ALLOC
3 .rodata 00000004 0000000000000000 0000000000000000 000000a0 2**0
CONTENTS, ALLOC, LOAD, READONLY, DATA
4 .comment 00000036 0000000000000000 0000000000000000 000000a4 2**0
CONTENTS, READONLY
5 .note.GNU-stack 00000000 0000000000000000 0000000000000000 000000da 2**0
CONTENTS, READONLY
6 .eh_frame 00000058 0000000000000000 0000000000000000 000000e0 2**3
CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
4.2 size SimpleSection.o
text data bss dec hex filename
177 8 4 189 bd SimpleSection.o
4.3 objdump -s -d SimpleSection.o
显示信息太多就不贴了。。。
4.4 objdump -r SimpleSection.o
SimpleSection.o: file format elf64-x86-64
RELOCATION RECORDS FOR [.text]:
OFFSET TYPE VALUE
0000000000000011 R_X86_64_32 .rodata
000000000000001b R_X86_64_PC32 printf-0x0000000000000004
0000000000000033 R_X86_64_PC32 .data
0000000000000039 R_X86_64_PC32 .bss-0x0000000000000004
000000000000004c R_X86_64_PC32 func1-0x0000000000000004
RELOCATION RECORDS FOR [.eh_frame]:
OFFSET TYPE VALUE
0000000000000020 R_X86_64_PC32 .text
0000000000000040 R_X86_64_PC32 .text+0x0000000000000022
4.5 readelf -h SimpleSection.o
ELF Header:
Magic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
Class: ELF64
Data: 2's complement, little endian
Version: 1 (current)
OS/ABI: UNIX - System V
ABI Version: 0
Type: REL (Relocatable file)
Machine: Advanced Micro Devices X86-64
Version: 0x1
Entry point address: 0x0
Start of program headers: 0 (bytes into file)
Start of section headers: 1072 (bytes into file)
Flags: 0x0
Size of this header: 64 (bytes)
Size of program headers: 0 (bytes)
Number of program headers: 0
Size of section headers: 64 (bytes)
Number of section headers: 13
Section header string table index: 10
4.6 readelf -S SimpleSection.o
There are 13 section headers, starting at offset 0x430:
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
0000000000000055 0000000000000000 AX 0 0 1
[ 2] .rela.text RELA 0000000000000000 00000320
0000000000000078 0000000000000018 I 11 1 8
[ 3] .data PROGBITS 0000000000000000 00000098
0000000000000008 0000000000000000 WA 0 0 4
[ 4] .bss NOBITS 0000000000000000 000000a0
0000000000000004 0000000000000000 WA 0 0 4
[ 5] .rodata PROGBITS 0000000000000000 000000a0
0000000000000004 0000000000000000 A 0 0 1
[ 6] .comment PROGBITS 0000000000000000 000000a4
0000000000000036 0000000000000001 MS 0 0 1
[ 7] .note.GNU-stack PROGBITS 0000000000000000 000000da
0000000000000000 0000000000000000 0 0 1
[ 8] .eh_frame PROGBITS 0000000000000000 000000e0
0000000000000058 0000000000000000 A 0 0 8
[ 9] .rela.eh_frame RELA 0000000000000000 00000398
0000000000000030 0000000000000018 I 11 8 8
[10] .shstrtab STRTAB 0000000000000000 000003c8
0000000000000061 0000000000000000 0 0 1
[11] .symtab SYMTAB 0000000000000000 00000138
0000000000000180 0000000000000018 12 11 8
[12] .strtab STRTAB 0000000000000000 000002b8
0000000000000066 0000000000000000 0 0 1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings), l (large)
I (info), L (link order), G (group), T (TLS), E (exclude), x (unknown)
O (extra OS processing required) o (OS specific), p (processor specific)
4.7 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.1839
7: 0000000000000000 4 OBJECT LOCAL DEFAULT 4 static_var2.1840
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 34 FUNC GLOBAL DEFAULT 1 func1
14: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND printf
15: 0000000000000022 51 FUNC GLOBAL DEFAULT 1 main
4.8 readelf -h SimpleSection.o
ELF Header:
Magic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
Class: ELF64
Data: 2's complement, little endian
Version: 1 (current)
OS/ABI: UNIX - System V
ABI Version: 0
Type: REL (Relocatable file)
Machine: Advanced Micro Devices X86-64
Version: 0x1
Entry point address: 0x0
Start of program headers: 0 (bytes into file)
Start of section headers: 1072 (bytes into file)
Flags: 0x0
Size of this header: 64 (bytes)
Size of program headers: 0 (bytes)
Number of program headers: 0
Size of section headers: 64 (bytes)
Number of section headers: 13
Section header string table index: 10
五，总结
本文主要讲了elf文件的常用命令，供参考。欢迎一起讨论交流~
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