UNIX中的SIZE命令

以下是我的C文件
int main()
{
    return 36;
}

它只包含return语句.但是,如果我使用size命令,它会显示
输出如下:

mohanraj@ltsp63:~/Development/chap8$size a.out 
text       data     bss     dec     hex filename
1056        252       8    1316     524 a.out
mohanraj@ltsp63:~/Development/chap8$

即使我的程序不包含任何全局变量或未声明的数据.但是,输出显示数据段有252个,bss有8个字节.那么,为什么输出是这样的呢?什么是252和8指.

大小命令

首先看每列的定义:

> text – cpu要执行的实际机器指令. Linux允许共享此数据.
> data – 程序中声明的所有初始化变量(声明)(例如,浮动薪水= 123.45;).
> bss – BSS由未初始化的数据组成,例如您没有设置任何值的数组或空指针.

正如蓝月亮所说.在Linux上,执行从调用_start()函数开始.哪个环境设置.每个C程序都隐藏了“库”,这取决于您使用的编译器.有全局参数,退出调用的设置,完成配置后,它最终调用main()函数.
ASFAIK无法通过配置和_start()函数查看代码的外观.但我可以告诉你,即使你的代码包含的信息也比你认为的更接近我们的硬件.

暗示:
输入readelf -a a.out来查看你的exec真正携带了多少信息.

里面是什么?

不要将源文件中的代码与可执行文件的大小进行比较,这取决于操作系统,编译器和使用的库.

在我的示例中,使用完全相同的代码,SIZE返回:

eryk@eryk-pc:~$gcc a.c 
eryk@eryk-pc:~$size a.out 
   text    data     bss     dec     hex filename
   1033     276       4    1313     521 a.out

让我们看看里面是什么……

eryk@eryk-pc:~$gcc -S a.c

这将在a.c上运行预处理器,执行初始编译,然后在运行汇编程序之前停止.

eryk@eryk-pc:~$cat a.s
    .file   "a.c"
    .text
    .globl  main
    .type   main,@function
main:
.LFB0:
    .cfi_startproc
    pushl   %ebp
    .cfi_def_cfa_offset 8
    .cfi_offset 5,-8
    movl    %esp,%ebp
    .cfi_def_cfa_register 5
    movl    $36,%eax
    popl    %ebp
    .cfi_restore 5
    .cfi_def_cfa 4,4
    ret
    .cfi_endproc
.LFE0:
    .size   main,.-main
    .ident  "GCC: (Ubuntu 4.8.2-19ubuntu1) 4.8.2"
    .section    .note.GNU-stack,"",@progbits

然后查看汇编代码

eryk@eryk-pc:~$objdump -d -M intel -S a.out

a.out:     file format elf32-i386


Disassembly of section .init:

08048294 <_init>:
 8048294:   53                      push   ebx
 8048295:   83 ec 08                sub    esp,0x8
 8048298:   e8 83 00 00 00          call   8048320 <__x86.get_pc_thunk.bx>
 804829d:   81 c3 63 1d 00 00       add    ebx,0x1d63
 80482a3:   8b 83 fc ff ff ff       mov    eax,DWORD PTR [ebx-0x4]
 80482a9:   85 c0                   test   eax,eax
 80482ab:   74 05                   je     80482b2 <_init+0x1e>
 80482ad:   e8 1e 00 00 00          call   80482d0 <__gmon_start__@plt>
 80482b2:   83 c4 08                add    esp,0x8
 80482b5:   5b                      pop    ebx
 80482b6:   c3                      ret    

Disassembly of section .plt:

080482c0 <__gmon_start__@plt-0x10>:
 80482c0:   ff 35 04 a0 04 08       push   DWORD PTR ds:0x804a004
 80482c6:   ff 25 08 a0 04 08       jmp    DWORD PTR ds:0x804a008
 80482cc:   00 00                   add    BYTE PTR [eax],al
    ...

080482d0 <__gmon_start__@plt>:
 80482d0:   ff 25 0c a0 04 08       jmp    DWORD PTR ds:0x804a00c
 80482d6:   68 00 00 00 00          push   0x0
 80482db:   e9 e0 ff ff ff          jmp    80482c0 <_init+0x2c>

080482e0 <__libc_start_main@plt>:
 80482e0:   ff 25 10 a0 04 08       jmp    DWORD PTR ds:0x804a010
 80482e6:   68 08 00 00 00          push   0x8
 80482eb:   e9 d0 ff ff ff          jmp    80482c0 <_init+0x2c>

Disassembly of section .text:

080482f0 <_start>:
 80482f0:   31 ed                   xor    ebp,ebp
 80482f2:   5e                      pop    esi
 80482f3:   89 e1                   mov    ecx,esp
 80482f5:   83 e4 f0                and    esp,0xfffffff0
 80482f8:   50                      push   eax
 80482f9:   54                      push   esp
 80482fa:   52                      push   edx
 80482fb:   68 70 84 04 08          push   0x8048470
 8048300:   68 00 84 04 08          push   0x8048400
 8048305:   51                      push   ecx
 8048306:   56                      push   esi
 8048307:   68 ed 83 04 08          push   0x80483ed
 804830c:   e8 cf ff ff ff          call   80482e0 <__libc_start_main@plt>
 8048311:   f4                      hlt    
 8048312:   66 90                   xchg   ax,ax
 8048314:   66 90                   xchg   ax,ax
 8048316:   66 90                   xchg   ax,ax
 8048318:   66 90                   xchg   ax,ax
 804831a:   66 90                   xchg   ax,ax
 804831c:   66 90                   xchg   ax,ax
 804831e:   66 90                   xchg   ax,ax

08048320 <__x86.get_pc_thunk.bx>:
 8048320:   8b 1c 24                mov    ebx,DWORD PTR [esp]
 8048323:   c3                      ret    
 8048324:   66 90                   xchg   ax,ax
 8048326:   66 90                   xchg   ax,ax
 8048328:   66 90                   xchg   ax,ax
 804832a:   66 90                   xchg   ax,ax
 804832c:   66 90                   xchg   ax,ax
 804832e:   66 90                   xchg   ax,ax

08048330 <deregister_tm_clones>:
 8048330:   b8 1f a0 04 08          mov    eax,0x804a01f
 8048335:   2d 1c a0 04 08          sub    eax,0x804a01c
 804833a:   83 f8 06                cmp    eax,0x6
 804833d:   77 01                   ja     8048340 <deregister_tm_clones+0x10>
 804833f:   c3                      ret    
 8048340:   b8 00 00 00 00          mov    eax,0x0
 8048345:   85 c0                   test   eax,eax
 8048347:   74 f6                   je     804833f <deregister_tm_clones+0xf>
 8048349:   55                      push   ebp
 804834a:   89 e5                   mov    ebp,esp
 804834c:   83 ec 18                sub    esp,0x18
 804834f:   c7 04 24 1c a0 04 08    mov    DWORD PTR [esp],0x804a01c
 8048356:   ff d0                   call   eax
 8048358:   c9                      leave  
 8048359:   c3                      ret    
 804835a:   8d b6 00 00 00 00       lea    esi,[esi+0x0]

08048360 <register_tm_clones>:
 8048360:   b8 1c a0 04 08          mov    eax,0x804a01c
 8048365:   2d 1c a0 04 08          sub    eax,0x804a01c
 804836a:   c1 f8 02                sar    eax,0x2
 804836d:   89 c2                   mov    edx,eax
 804836f:   c1 ea 1f                shr    edx,0x1f
 8048372:   01 d0                   add    eax,edx
 8048374:   d1 f8                   sar    eax,1
 8048376:   75 01                   jne    8048379 <register_tm_clones+0x19>
 8048378:   c3                      ret    
 8048379:   ba 00 00 00 00          mov    edx,0x0
 804837e:   85 d2                   test   edx,edx
 8048380:   74 f6                   je     8048378 <register_tm_clones+0x18>
 8048382:   55                      push   ebp
 8048383:   89 e5                   mov    ebp,esp
 8048385:   83 ec 18                sub    esp,0x18
 8048388:   89 44 24 04             mov    DWORD PTR [esp+0x4],eax
 804838c:   c7 04 24 1c a0 04 08    mov    DWORD PTR [esp],0x804a01c
 8048393:   ff d2                   call   edx
 8048395:   c9                      leave  
 8048396:   c3                      ret    
 8048397:   89 f6                   mov    esi,esi
 8048399:   8d bc 27 00 00 00 00    lea    edi,[edi+eiz*1+0x0]

080483a0 <__do_global_dtors_aux>:
 80483a0:   80 3d 1c a0 04 08 00    cmp    BYTE PTR ds:0x804a01c,0x0
 80483a7:   75 13                   jne    80483bc <__do_global_dtors_aux+0x1c>
 80483a9:   55                      push   ebp
 80483aa:   89 e5                   mov    ebp,esp
 80483ac:   83 ec 08                sub    esp,0x8
 80483af:   e8 7c ff ff ff          call   8048330 <deregister_tm_clones>
 80483b4:   c6 05 1c a0 04 08 01    mov    BYTE PTR ds:0x804a01c,0x1
 80483bb:   c9                      leave  
 80483bc:   f3 c3                   repz ret 
 80483be:   66 90                   xchg   ax,ax

080483c0 <frame_dummy>:
 80483c0:   a1 10 9f 04 08          mov    eax,ds:0x8049f10
 80483c5:   85 c0                   test   eax,eax
 80483c7:   74 1f                   je     80483e8 <frame_dummy+0x28>
 80483c9:   b8 00 00 00 00          mov    eax,0x0
 80483ce:   85 c0                   test   eax,eax
 80483d0:   74 16                   je     80483e8 <frame_dummy+0x28>
 80483d2:   55                      push   ebp
 80483d3:   89 e5                   mov    ebp,esp
 80483d5:   83 ec 18                sub    esp,0x18
 80483d8:   c7 04 24 10 9f 04 08    mov    DWORD PTR [esp],0x8049f10
 80483df:   ff d0                   call   eax
 80483e1:   c9                      leave  
 80483e2:   e9 79 ff ff ff          jmp    8048360 <register_tm_clones>
 80483e7:   90                      nop
 80483e8:   e9 73 ff ff ff          jmp    8048360 <register_tm_clones>

080483ed <main>:
 80483ed:   55                      push   ebp
 80483ee:   89 e5                   mov    ebp,esp
 80483f0:   b8 24 00 00 00          mov    eax,0x24
 80483f5:   5d                      pop    ebp
 80483f6:   c3                      ret    
 80483f7:   66 90                   xchg   ax,ax
 80483f9:   66 90                   xchg   ax,ax
 80483fb:   66 90                   xchg   ax,ax
 80483fd:   66 90                   xchg   ax,ax
 80483ff:   90                      nop

08048400 <__libc_csu_init>:
 8048400:   55                      push   ebp
 8048401:   57                      push   edi
 8048402:   31 ff                   xor    edi,edi
 8048404:   56                      push   esi
 8048405:   53                      push   ebx
 8048406:   e8 15 ff ff ff          call   8048320 <__x86.get_pc_thunk.bx>
 804840b:   81 c3 f5 1b 00 00       add    ebx,0x1bf5
 8048411:   83 ec 1c                sub    esp,0x1c
 8048414:   8b 6c 24 30             mov    ebp,DWORD PTR [esp+0x30]
 8048418:   8d b3 0c ff ff ff       lea    esi,[ebx-0xf4]
 804841e:   e8 71 fe ff ff          call   8048294 <_init>
 8048423:   8d 83 08 ff ff ff       lea    eax,[ebx-0xf8]
 8048429:   29 c6                   sub    esi,eax
 804842b:   c1 fe 02                sar    esi,0x2
 804842e:   85 f6                   test   esi,esi
 8048430:   74 27                   je     8048459 <__libc_csu_init+0x59>
 8048432:   8d b6 00 00 00 00       lea    esi,[esi+0x0]
 8048438:   8b 44 24 38             mov    eax,DWORD PTR [esp+0x38]
 804843c:   89 2c 24                mov    DWORD PTR [esp],ebp
 804843f:   89 44 24 08             mov    DWORD PTR [esp+0x8],eax
 8048443:   8b 44 24 34             mov    eax,DWORD PTR [esp+0x34]
 8048447:   89 44 24 04             mov    DWORD PTR [esp+0x4],eax
 804844b:   ff 94 bb 08 ff ff ff    call   DWORD PTR [ebx+edi*4-0xf8]
 8048452:   83 c7 01                add    edi,0x1
 8048455:   39 f7                   cmp    edi,esi
 8048457:   75 df                   jne    8048438 <__libc_csu_init+0x38>
 8048459:   83 c4 1c                add    esp,0x1c
 804845c:   5b                      pop    ebx
 804845d:   5e                      pop    esi
 804845e:   5f                      pop    edi
 804845f:   5d                      pop    ebp
 8048460:   c3                      ret    
 8048461:   eb 0d                   jmp    8048470 <__libc_csu_fini>
 8048463:   90                      nop
 8048464:   90                      nop
 8048465:   90                      nop
 8048466:   90                      nop
 8048467:   90                      nop
 8048468:   90                      nop
 8048469:   90                      nop
 804846a:   90                      nop
 804846b:   90                      nop
 804846c:   90                      nop
 804846d:   90                      nop
 804846e:   90                      nop
 804846f:   90                      nop

08048470 <__libc_csu_fini>:
 8048470:   f3 c3                   repz ret 

Disassembly of section .fini:

08048474 <_fini>:
 8048474:   53                      push   ebx
 8048475:   83 ec 08                sub    esp,0x8
 8048478:   e8 a3 fe ff ff          call   8048320 <__x86.get_pc_thunk.bx>
 804847d:   81 c3 83 1b 00 00       add    ebx,0x1b83
 8048483:   83 c4 08                add    esp,0x8
 8048486:   5b                      pop    ebx
 8048487:   c3                      ret

下一步将上面的代码转换为01表示法.

如你看到的.即使是简单的c程序也包含复杂的操作,代码的硬件越接近硬件.我希望我已经向你解释了为什么可执行文件比你想象的要大.如果您有任何疑问,请随时评论我的帖子.我会马上编辑我的答案.

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