内存寻址

#include <stdio.h>
greeting()
{
printf("Hello, world!\n");
}
main()
{
greeting();
}
08048368 <greeting>:
 8048368:       55                      push   %ebp
 8048369:       89 e5                   mov    %esp,%ebp
 804836b:       83 ec 08                sub    $0x8,%esp
 804836e:       83 ec 0c                sub    $0xc,%esp
 8048371:       68 84 84 04 08          push   $0x8048484
 8048376:       e8 35 ff ff ff          call   80482b0 <printf@plt>
 804837b:       83 c4 10                add    $0x10,%esp
 804837e:       c9                      leave
37
 804837f:       c3                      ret
08048380 <main>:
 8048380:       55                      push   %ebp
 8048381:       89 e5                   mov    %esp,%ebp
 8048383:       83 ec 08                sub    $0x8,%esp
 8048386:       83 e4 f0                and    $0xfffffff0,%esp
 8048389:       b8 00 00 00 00          mov    $0x0,%eax
 804838e:       83 c0 0f                add    $0xf,%eax
 8048391:       83 c0 0f                add    $0xf,%eax
 8048394:       c1 e8 04                shr    $0x4,%eax
 8048397:       c1 e0 04                shl    $0x4,%eax
 804839a:       29 c4                   sub    %eax,%esp
 804839c:       e8 c7 ff ff ff          call   8048368 <greeting>
 80483a1:       c9                      leave
 80483a2:       c3                      ret
 80483a3:       90                      nop
0x08048368是程序入口
1、从段寄存器开始取值，即段选择符
==================== include/asm-i386/segment.h 4 8 ====================
4 #define __KERNEL_CS 0x10
5 #define __KERNEL_DS 0x18
6
7 #define __USER_CS  0x23
8 #define __USER_DS  0x2B
2、然后根据__USER_CS  0x23找全局描述符表，找到如下的东西
450  ENTRY(gdt_table)
451 .quad 0x0000000000000000 /* NULL descriptor */
452 .quad 0x0000000000000000 /* not used */
453 .quad 0x00cf9a000000ffff /* 0x10 kernel 4GB code at 0x00000000 */
454 .quad 0x00cf92000000ffff /* 0x18 kernel 4GB data at 0x00000000 */
455 .quad 0x00cffa000000ffff /* 0x23 user   4GB code at 0x00000000 */
456 .quad 0x00cff2000000ffff /* 0x2b user   4GB data at 0x00000000 */
457 .quad 0x0000000000000000 /* not used */
458 .quad 0x0000000000000000 /* not used */

3、之后进行线性地址的页式转换
Linux实际将持续入口地址映射为自身0x08048368
0000  1000  0000  0100  1000  0011  0110  1000