首先看一段程序:
int printf(const char* fromat,...); 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; }
gcc -c SimpleSection.o
利用objdump -h命令将SimpleSection.o这个ELF文件的各个段基本信息打印出来,如下:
Sections:
Idx Name Size VMA LMA File off Algn
0 .text 0000004f 0000000000000000 0000000000000000 00000040 2**0
CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
1 .data 00000008 0000000000000000 0000000000000000 00000090 2**2
CONTENTS, ALLOC, LOAD, DATA
2 .bss 00000004 0000000000000000 0000000000000000 00000098 2**2
ALLOC
3 .rodata 00000006 0000000000000000 0000000000000000 00000098 2**0
CONTENTS, ALLOC, LOAD, READONLY, DATA
4 .comment 0000002e 0000000000000000 0000000000000000 0000009e 2**0
CONTENTS, READONLY
5 .note.GNU-stack 00000000 0000000000000000 0000000000000000 000000cc 2**0
CONTENTS, READONLY
6 .eh_frame 00000058 0000000000000000 0000000000000000 000000d0 2**3
CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
Idx Name Size VMA LMA File off Algn
0 .text 0000004f 0000000000000000 0000000000000000 00000040 2**0
CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
1 .data 00000008 0000000000000000 0000000000000000 00000090 2**2
CONTENTS, ALLOC, LOAD, DATA
2 .bss 00000004 0000000000000000 0000000000000000 00000098 2**2
ALLOC
3 .rodata 00000006 0000000000000000 0000000000000000 00000098 2**0
CONTENTS, ALLOC, LOAD, READONLY, DATA
4 .comment 0000002e 0000000000000000 0000000000000000 0000009e 2**0
CONTENTS, READONLY
5 .note.GNU-stack 00000000 0000000000000000 0000000000000000 000000cc 2**0
CONTENTS, READONLY
6 .eh_frame 00000058 0000000000000000 0000000000000000 000000d0 2**3
CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
除了基本的代码段、数据段(初始化的全局变量与局部静态变量)、BSS段(未初始化的全局变量和未初始化的局部静态变量)之外,还有之都数据段(
.rodata),注释信息段(
.comment),堆栈提示段(
.note.GNU-stack),调试信息段(
.eh_frame)。
其中
Size表示该段的大小,
File off表示段所在位置(距离ELF Header 00000000)的偏移。
CONTENTS, ALLOC等表示各段的属性。
CONTENTS表示该段在文件中存在,BSS段
其实在ELF中不存在内容。