在UNIX SIZE命令 [英] SIZE command in UNIX
问题描述
以下是我的C文件：
int main()
{
return 36;
}
它仅包含return语句。但是，如果使用大小命令，它显示了
这样的输出：
It contains only return statement. But if I use the size command, it shows the output like this:
mohanraj@ltsp63:~/Development/chap8$ size a.out
text data bss dec hex filename
1056 252 8 1316 524 a.out
mohanraj@ltsp63:~/Development/chap8$
虽然我的程序不包含任何全局变量，或者未申报的数据。但是，输出显示数据段有252和BSS有8个字节。那么，为什么输出是这个样子？什么是252和8指。
Even though my program does not contain any global variable, or undeclared data. But, the output shows data segment have 252 and the bss have 8 bytes. So, why the output is like this? what is 252 and 8 refers.
推荐答案
size命令
首先看到每个列的定义：
First see the definition of each column:
- 的文本的 - 你的CPU将执行实际的机器指令。 Linux允许共享这些数据。
- 的数据的 - 所有初始化的变量（声明）在程序中声明（例如，浮动工资= 123.45）。
- 的 BSS 的 - 该BSS包括未初始化的数据，如您没有设置任何值或空指针数组
- text - Actual machine instructions that your CPU going to execute. Linux allows to share this data.
- data - All initialized variables (declarations) declared in a program (e.g., float salary=123.45;).
- bss - The BSS consists of uninitialized data such as arrays that you have not set any values to or null pointers.
由于蓝月亮说。在Linux上，执行通过调用_start（）函数开始。这确实环境设置。每一个C程序都有隐藏的取决于你使用compilator库。有全局参数，退出通话设置并完成配置后，它终于调用您的main（）函数。
ASFAIK没有办法看到你的code相如何封装配置和_start（）函数。但我可以告诉你，甚至你的code含有比你想象的硬件，我们是接近的更多信息。
As Blue Moon said. On Linux, the execution starts by calling _start() function. Which does environment setup. Every C program has hidden "libraries" that depends on compilator you using. There are settings for global parameters, exit calls and after complete configuration it finally calls your main() function. ASFAIK there's no way to see how your code looks encapsulated with configuration and _start() function. But I can show you that even your code contains more information than you thought the closer to hardware we are.
的提示：的
键入 readelf -a的a.out 来看看你的真正的exec多少信息携带。
Hint:
Type readelf -a a.out to see how much information your exec really carrying.
里面是什么？
不要在您的源文件的可执行文件的大小比较code，这取决于操作系统，compilator和使用的库。
Do not compare code in your source file to the size of executable file, it depends on the OS, compilator, and used libraries.
在我的例子中，具有完全相同的code，大小，则返回：
In my example, with exactly the same code, SIZE returns:
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
让我们来看看里面是什么...
Let's see what is inside...
eryk@eryk-pc:~$ gcc -S a.c
这将运行在交流转换器的preprocessor，执行初始编译，然后停止汇编程序运行之前。
This will run the preprocessor over a.c, perform the initial compilation and then stop before the assembler is run.
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 $36, %eax
popl %ebp
.cfi_restore 5
.cfi_def_cfa 4, 4
ret
.cfi_endproc
.LFE0:
.size main, .-main
.ident "GCC: (Ubuntu 4.8.2-19ubuntu1) 4.8.2"
.section .note.GNU-stack,"",@progbits
然后再看看对装配code
Then look on the assembly code
eryk@eryk-pc:~$ 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
下一步将转换高于code至01记号。
Next step would converting above code to 01 notation.
正如你所看到的。即使是简单的C程序中包含复杂的操作硬件的code是密切。我希望，为什么可执行文件是比你想象的大我已经向你解释。如果您有任何疑问，请随时发表评论我的职务。我会立即编辑我的答案。
As you can see. Even simple c program contains complicated operation the closer to hardware your code is. I hope I have explained to you why the executable file is bigger than you thought. If you have any doubts, feel free to comment my post. I will edit my answer immediately.
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