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ELF header(ELF 头部)
Program header table( 程序头表)
Segment1 （段1 ）
Segment2 （段2 ）
………
Sengmentn （段n ）
Setion header table( 节头表，可选)// 描述了映射加载关系，可由OBJDUMP 查看objdump -h 我的程序
Unix 系统在可执行文件的加载过程中，除了读取必要的头部信息，并没有任何从磁盘到存储器的数据拷贝，只是简单进行映射，知道 CPU 访问一个被映射的虚拟页产生缺页异常后，才进行拷贝。
| 地址 | 作用 | 说明 |
| >=0xc000 0000 | 内核虚拟存储器 | 系统保留区 |
| <0xc000 0000 | Stack （用户栈） | %EBP,%ESP |
|
| ↓
↑ |
空闲/ 动态库也放在此 |
| >=0x4000 0000 | 文件映射区 | 只映射，page fault 后加载 |
| <0x4000 0000 |
↑ |
空闲
|
|
| Heap( 运行时堆) | 通过brk/sbrk 系统调用扩大堆，向上增长(malloc) 。 |
|
| .data 、.bss( 读写段) | 可执行文件中获取，重定位 |
| >=0x0804 8000 | .init 、.text 、.rodata( 只读段) | 可执行文件中获取，重定位 |
| <0x0804 8000 | 保留区域 |
|
C 程序的入口点是 _start ，这段启动代码是在目标文件 ctrl.o 中定义的。启动代码中首先调用初始化函数，然后调用 atexit 函数，用于注册在 exit 函数被调用 ( 程序退出 ) 时应该被调用的函数。最后，启动代码调用 main 函数，在 main 函数返回后，调用系统调用 _exit() ，将控制返回给操作系统。
