linux汇编语言的call指令

学习系统调用，编了一个程序
void main()
{
    write(1, "hello\n", 6);
    exit(0);
}
下面是生成的汇编代码
    .file   "syscall.c"
    .section    .rodata
.LC0:
    .string "hello\n"
    .text
.globl main
    .type   main, @function
main:
.LFB0:
    .cfi_startproc
    pushq   %rbp
    .cfi_def_cfa_offset 16
    movq    %rsp, %rbp
    .cfi_offset 6, -16
    .cfi_def_cfa_register 6
    movl    $6, %edx
    movl    $.LC0, %esi
    movl    $1, %edi
    movl    $0, %eax
    call    write          //请问这句调用的write，具体是怎么实现的？书里面介绍的，是用int $0x80这个陷阱来实现的系统调用，这个write对int $0x80封装了么？去哪里找？
    movl    $0, %edi
    call    exit       / /这句也一样
    .cfi_endproc
.LFE0:
    .size   main, .-main
    .ident  "GCC: (Ubuntu/Linaro 4.4.4-14ubuntu5) 4.4.5"
    .section    .note.GNU-stack,"",@progbits

希望会的朋友指点！谢谢了！

7 个解决方案

#1

lz用什么方式得到汇编的呢，偶使用 objdump -d 得到的东西和lz不太一样呢

#2

首先write的函数肯定是具有默认连接的，就是说：比如一个printf（）函数，有的IDE环境需要加头文件#include<stdio.h>但是有的环境不需要加头文件也能编译连接！这个write函数是一个库函数！要想找这个函数只能找你的默认目录下找到（每个系统不一样）。

#3

引用 1 楼 ytmayer 的回复:

lz用什么方式得到汇编的呢，偶使用 objdump -d 得到的东西和lz不太一样呢

我是用GCC直接-S生成的，可能像2楼的兄弟说的，还未链接。我用objdump反汇编出来的，看不懂，还是没有找到int 0x80这个软中断指令啊

#4

引用 2 楼 wanghb1989 的回复:

首先write的函数肯定是具有默认连接的，就是说：比如一个printf（）函数，有的IDE环境需要加头文件#include<stdio.h>但是有的环境不需要加头文件也能编译连接！这个write函数是一个库函数！要想找这个函数只能找你的默认目录下找到（每个系统不一样）。

那么生成可执行文件再反汇编是链接以后的代码吗？这是用objdump生成的，麻烦看看
./syscall:     file format elf64-x86-64


Disassembly of section .init:

0000000000400400 <_init>:
  400400:       48 83 ec 08             sub    $0x8,%rsp
  400404:       e8 83 00 00 00          callq  40048c <call_gmon_start>
  400409:       e8 12 01 00 00          callq  400520 <frame_dummy>
  40040e:       e8 fd 01 00 00          callq  400610 <__do_global_ctors_aux>
  400413:       48 83 c4 08             add    $0x8,%rsp
  400417:       c3                      retq

Disassembly of section .plt:

0000000000400418 <exit@plt-0x10>:
  400418:       ff 35 d2 0b 20 00       pushq  0x200bd2(%rip)        # 600ff0 <_GLOBAL_OFFSET_TABLE_+0x8>
  40041e:       ff 25 d4 0b 20 00       jmpq   *0x200bd4(%rip)        # 600ff8 <_GLOBAL_OFFSET_TABLE_+0x10>
  400424:       0f 1f 40 00             nopl   0x0(%rax)

0000000000400428 <exit@plt>:
  400428:       ff 25 d2 0b 20 00       jmpq   *0x200bd2(%rip)        # 601000 <_GLOBAL_OFFSET_TABLE_+0x18>
  40042e:       68 00 00 00 00          pushq  $0x0
  400433:       e9 e0 ff ff ff          jmpq   400418 <_init+0x18>

0000000000400438 <__libc_start_main@plt>:
  400438:       ff 25 ca 0b 20 00       jmpq   *0x200bca(%rip)        # 601008 <_GLOBAL_OFFSET_TABLE_+0x20>
  40043e:       68 01 00 00 00          pushq  $0x1
  400443:       e9 d0 ff ff ff          jmpq   400418 <_init+0x18>

0000000000400448 <write@plt>:               //这里就是调用write的地方吧？怎么解释这段代码呢？看不懂唉
  400448:       ff 25 c2 0b 20 00       jmpq   *0x200bc2(%rip)        # 601010 <_GLOBAL_OFFSET_TABLE_+0x28>
  40044e:       68 02 00 00 00          pushq  $0x2
  400453:       e9 c0 ff ff ff          jmpq   400418 <_init+0x18>

Disassembly of section .text:

0000000000400460 <_start>:
  400460:       31 ed                   xor    %ebp,%ebp
  400462:       49 89 d1                mov    %rdx,%r9
  400465:       5e                      pop    %rsi
  400466:       48 89 e2                mov    %rsp,%rdx
  400469:       48 83 e4 f0             and    $0xfffffffffffffff0,%rsp
  40046d:       50                      push   %rax
  40046e:       54                      push   %rsp
  40046f:       49 c7 c0 70 05 40 00    mov    $0x400570,%r8
  400476:       48 c7 c1 80 05 40 00    mov    $0x400580,%rcx
  40047d:       48 c7 c7 44 05 40 00    mov    $0x400544,%rdi
  400484:       e8 af ff ff ff          callq  400438 <__libc_start_main@plt>
  400489:       f4                      hlt
  40048a:       90                      nop
  40048b:       90                      nop

000000000040048c <call_gmon_start>:
  40048c:       48 83 ec 08             sub    $0x8,%rsp
  400490:       48 8b 05 49 0b 20 00    mov    0x200b49(%rip),%rax        # 600fe0 <_DYNAMIC+0x190>
  400497:       48 85 c0                test   %rax,%rax
  40049a:       74 02                   je     40049e <call_gmon_start+0x12>
  40049c:       ff d0                   callq  *%rax
  40049e:       48 83 c4 08             add    $0x8,%rsp
  4004a2:       c3                      retq
  4004a3:       90                      nop
  4004a4:       90                      nop
  4004a5:       90                      nop
  4004a6:       90                      nop
  4004a7:       90                      nop
  4004a8:       90                      nop
  4004a9:       90                      nop
  4004aa:       90                      nop
  4004ab:       90                      nop
  4004ac:       90                      nop
  4004ad:       90                      nop
  4004ae:       90                      nop
  4004af:       90                      nop

00000000004004b0 <__do_global_dtors_aux>:
  4004b0:       55                      push   %rbp
  4004b1:       48 89 e5                mov    %rsp,%rbp
  4004b4:       53                      push   %rbx
  4004b5:       48 83 ec 08             sub    $0x8,%rsp
  4004b9:       80 3d 68 0b 20 00 00    cmpb   $0x0,0x200b68(%rip)        # 601028 <__bss_start>
  4004c0:       75 4b                   jne    40050d <__do_global_dtors_aux+0x5d>
  4004c2:       bb 40 0e 60 00          mov    $0x600e40,%ebx
  4004c7:       48 8b 05 62 0b 20 00    mov    0x200b62(%rip),%rax        # 601030 <dtor_idx.7426>
  4004ce:       48 81 eb 38 0e 60 00    sub    $0x600e38,%rbx
  4004d5:       48 c1 fb 03             sar    $0x3,%rbx
  4004d9:       48 83 eb 01             sub    $0x1,%rbx
  4004dd:       48 39 d8                cmp    %rbx,%rax
  4004e0:       73 24                   jae    400506 <__do_global_dtors_aux+0x56>
  4004e2:       eb 04                   jmp    4004e8 <__do_global_dtors_aux+0x38>
  4004e4:       90                      nop
  4004e5:       90                      nop
  4004e6:       90                      nop
  4004e7:       90                      nop
  4004e8:       48 83 c0 01             add    $0x1,%rax
  4004ec:       48 89 05 3d 0b 20 00    mov    %rax,0x200b3d(%rip)        # 601030 <dtor_idx.7426>
  4004f3:       ff 14 c5 38 0e 60 00    callq  *0x600e38(,%rax,8)
  4004fa:       48 8b 05 2f 0b 20 00    mov    0x200b2f(%rip),%rax        # 601030 <dtor_idx.7426>
  400501:       48 39 d8                cmp    %rbx,%rax
  400504:       72 e2                   jb     4004e8 <__do_global_dtors_aux+0x38>
  400506:       c6 05 1b 0b 20 00 01    movb   $0x1,0x200b1b(%rip)        # 601028 

#5

接楼上代码
<__bss_start>
  40050d:       48 83 c4 08             add    $0x8,%rsp
  400511:       5b                      pop    %rbx
  400512:       c9                      leaveq
  400513:       c3                      retq
  400514:       eb 0a                   jmp    400520 <frame_dummy>
  400516:       90                      nop
  400517:       90                      nop
  400518:       90                      nop
  400519:       90                      nop
  40051a:       90                      nop
  40051b:       90                      nop
  40051c:       90                      nop
  40051d:       90                      nop
  40051e:       90                      nop
  40051f:       90                      nop

0000000000400520 <frame_dummy>:
  400520:       55                      push   %rbp
  400521:       48 83 3d 1f 09 20 00    cmpq   $0x0,0x20091f(%rip)        # 600e48 <__JCR_END__>
  400528:       00
  400529:       48 89 e5                mov    %rsp,%rbp
  40052c:       74 12                   je     400540 <frame_dummy+0x20>
  40052e:       b8 00 00 00 00          mov    $0x0,%eax
  400533:       48 85 c0                test   %rax,%rax
  400536:       74 08                   je     400540 <frame_dummy+0x20>
  400538:       bf 48 0e 60 00          mov    $0x600e48,%edi
  40053d:       c9                      leaveq
  40053e:       ff e0                   jmpq   *%rax
  400540:       c9                      leaveq
  400541:       c3                      retq
  400542:       90                      nop
  400543:       90                      nop

0000000000400544 <main>:
  400544:       55                      push   %rbp
  400545:       48 89 e5                mov    %rsp,%rbp
  400548:       ba 06 00 00 00          mov    $0x6,%edx
  40054d:       be 5c 06 40 00          mov    $0x40065c,%esi
  400552:       bf 01 00 00 00          mov    $0x1,%edi
  400557:       b8 00 00 00 00          mov    $0x0,%eax
  40055c:       e8 e7 fe ff ff          callq  400448 <write@plt>
  400561:       bf 00 00 00 00          mov    $0x0,%edi
  400566:       e8 bd fe ff ff          callq  400428 <exit@plt>
  40056b:       90                      nop
  40056c:       90                      nop
  40056d:       90                      nop
  40056e:       90                      nop
  40056f:       90                      nop

0000000000400570 <__libc_csu_fini>:
  400570:       f3 c3                   repz retq
  400572:       eb 0c                   jmp    400580 <__libc_csu_init>
  400574:       90                      nop
  400575:       90                      nop
  400576:       90                      nop
  400577:       90                      nop
  400578:       90                      nop
  400579:       90                      nop
  40057a:       90                      nop
  40057b:       90                      nop
  40057c:       90                      nop
  40057d:       90                      nop
  40057e:       90                      nop
  40057f:       90                      nop

0000000000400580 <__libc_csu_init>:
  400580:       48 89 6c 24 d8          mov    %rbp,-0x28(%rsp)
  400585:       4c 89 64 24 e0          mov    %r12,-0x20(%rsp)
  40058a:       48 8d 2d 93 08 20 00    lea    0x200893(%rip),%rbp        # 600e24 <__init_array_end>
  400591:       4c 8d 25 8c 08 20 00    lea    0x20088c(%rip),%r12        # 600e24 <__init_array_end>
  400598:       4c 89 6c 24 e8          mov    %r13,-0x18(%rsp)
  40059d:       4c 89 74 24 f0          mov    %r14,-0x10(%rsp)
  4005a2:       4c 89 7c 24 f8          mov    %r15,-0x8(%rsp)
  4005a7:       48 89 5c 24 d0          mov    %rbx,-0x30(%rsp)
  4005ac:       48 83 ec 38             sub    $0x38,%rsp
  4005b0:       4c 29 e5                sub    %r12,%rbp
  4005b3:       41 89 fd                mov    %edi,%r13d
  4005b6:       49 89 f6                mov    %rsi,%r14
  4005b9:       48 c1 fd 03             sar    $0x3,%rbp
  4005bd:       49 89 d7                mov    %rdx,%r15
  4005c0:       e8 3b fe ff ff          callq  400400 <_init>
  4005c5:       48 85 ed                test   %rbp,%rbp
  4005c8:       74 1c                   je     4005e6 <__libc_csu_init+0x66>
  4005ca:       31 db                   xor    %ebx,%ebx
  4005cc:       eb 02                   jmp    4005d0 <__libc_csu_init+0x50>
  4005ce:       90                      nop
  4005cf:       90                      nop
  4005d0:       4c 89 fa                mov    %r15,%rdx
  4005d3:       4c 89 f6                mov    %r14,%rsi
  4005d6:       44 89 ef                mov    %r13d,%edi
  4005d9:       41 ff 14 dc             callq  *(%r12,%rbx,8)
  4005dd:       48 83 c3 01             add    $0x1,%rbx
  4005e1:       48 39 eb                cmp    %rbp,%rbx
  4005e4:       72 ea                   jb     4005d0 <__libc_csu_init+0x50>
  4005e6:       48 8b 5c 24 08          mov    0x8(%rsp),%rbx
  4005eb:       48 8b 6c 24 10          mov    0x10(%rsp),%rbp
  4005f0:       4c 8b 64 24 18          mov    0x18(%rsp),%r12
  4005f5:       4c 8b 6c 24 20          mov    0x20(%rsp),%r13
  4005fa:       4c 8b 74 24 28          mov    0x28(%rsp),%r14
  4005ff:       4c 8b 7c 24 30          mov    0x30(%rsp),%r15
  400604:       48 83 c4 38             add    $0x38,%rsp
  400608:       c3                      retq
  400609:       90                      nop
  40060a:       90                      nop
  40060b:       90                      nop
  40060c:       90                      nop
  40060d:       90                      nop
  40060e:       90                      nop
  40060f:       90                      nop

0000000000400610 <__do_global_ctors_aux>:
  400610:       55                      push   %rbp
  400611:       48 89 e5                mov    %rsp,%rbp
  400614:       53                      push   %rbx
  400615:       48 83 ec 08             sub    $0x8,%rsp
  400619:       48 8b 05 08 08 20 00    mov    0x200808(%rip),%rax        # 600e28 <__CTOR_LIST__>
  400620:       48 83 f8 ff             cmp    $0xffffffffffffffff,%rax
  400624:       74 19                   je     40063f <__do_global_ctors_aux+0x2f>
  400626:       bb 28 0e 60 00          mov    $0x600e28,%ebx
  40062b:       eb 03                   jmp    400630 <__do_global_ctors_aux+0x20>
  40062d:       90                      nop
  40062e:       90                      nop
  40062f:       90                      nop
  400630:       48 83 eb 08             sub    $0x8,%rbx
  400634:       ff d0                   callq  *%rax
  400636:       48 8b 03                mov    (%rbx),%rax
  400639:       48 83 f8 ff             cmp    $0xffffffffffffffff,%rax
  40063d:       75 f1                   jne    400630 <__do_global_ctors_aux+0x20>
  40063f:       48 83 c4 08             add    $0x8,%rsp
  400643:       5b                      pop    %rbx
  400644:       c9                      leaveq
  400645:       c3                      retq
  400646:       90                      nop
  400647:       90                      nop

Disassembly of section .fini:

0000000000400648 <_fini>:
  400648:       48 83 ec 08             sub    $0x8,%rsp
  40064c:       e8 5f fe ff ff          callq  4004b0 <__do_global_dtors_aux>
  400651:       48 83 c4 08             add    $0x8,%rsp
  400655:       c3                      retq

#6

这个和动态链接有关，如果加-static选项编译出来就能看到不同的结果，我这边看到的是直接用syscall指令实现的

#7

引用 6 楼 ytmayer 的回复:

这个和动态链接有关，如果加-static选项编译出来就能看到不同的结果，我这边看到的是直接用syscall指令实现的

非常感谢！
但是syscall又是什么呢？是一条汇编指令？它和int 0x80一样吗？