linux中的nm命令简介

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linux中的nm命令简介
转：http://blog.csdn.net/stpeace/article/details/47089585

一般来说，搞linux开发的人，才会用到nm命令，非开发的人，应该用不到。虽然nm很简单，但是还是有必要写几句，聊表心意。

nm不是ni ma的缩写，当然，也不是ni mei的缩写，而是names的缩写， nm命令主要是用来列出某些文件中的符号（说白了就是一些函数和全局变量等）。下面，我们一起来看看。

test.h为：
[cpp] view plain copy print ?

void print();
```
void print();
```
test.c为：
[cpp] view plain copy print ?

#include <stdio.h>

#include "test.h"



void print()

{

    printf("rainy days ");

}
```
#include <stdio.h>
#include "test.h"

void print()
{
	printf("rainy days
");
}
```
main.c为：
[cpp] view plain copy print ?

#include "test.h"



int main()

{

    print();

    return 0;

}
```
#include "test.h"

int main()
{
	print();
	return 0;
}
```
好，我们看看nm命令的作用效果，如下：
[plain] view plain copy print ?

[taoge@localhost learn_nm]$ nm *

nm: main.c: File format not recognized

nm: test.c: File format not recognized

nm: test.h: File format not recognized

[taoge@localhost learn_nm]$
```
[taoge@localhost learn_nm]$ nm *
nm: main.c: File format not recognized
nm: test.c: File format not recognized
nm: test.h: File format not recognized
[taoge@localhost learn_nm]$ 
```
ni ma, 啥都没有，这说明nm对这类文件无用。

继续看nm能否读取目标文件和可执行文件：
[plain] view plain copy print ?

[taoge@localhost learn_nm]$ ls

main.c  test.c  test.h

[taoge@localhost learn_nm]$ gcc -c test.c main.c

[taoge@localhost learn_nm]$ gcc test.o main.o

[taoge@localhost learn_nm]$ ./a.out

rainy days

[taoge@localhost learn_nm]$ nm *



a.out:

08049564 d _DYNAMIC

08049630 d _GLOBAL_OFFSET_TABLE_

0804849c R _IO_stdin_used

         w _Jv_RegisterClasses

08049554 d __CTOR_END__

08049550 d __CTOR_LIST__

0804955c D __DTOR_END__

08049558 d __DTOR_LIST__

0804854c r __FRAME_END__

08049560 d __JCR_END__

08049560 d __JCR_LIST__

0804964c A __bss_start

08049648 D __data_start

08048450 t __do_global_ctors_aux

08048330 t __do_global_dtors_aux

080484a0 R __dso_handle

         w __gmon_start__

0804844a T __i686.get_pc_thunk.bx

08049550 d __init_array_end

08049550 d __init_array_start

080483e0 T __libc_csu_fini

080483f0 T __libc_csu_init

         U __libc_start_main@@GLIBC_2.0

0804964c A _edata

08049654 A _end

0804847c T _fini

08048498 R _fp_hw

08048290 T _init

08048300 T _start

0804964c b completed.5963

08049648 W data_start

08049650 b dtor_idx.5965

08048390 t frame_dummy

080483c8 T main

080483b4 T print

         U puts@@GLIBC_2.0

nm: main.c: File format not recognized



main.o:

00000000 T main

         U print

nm: test.c: File format not recognized

nm: test.h: File format not recognized



test.o:

00000000 T print

         U puts

[taoge@localhost learn_nm]$
```
[taoge@localhost learn_nm]$ ls
main.c  test.c  test.h
[taoge@localhost learn_nm]$ gcc -c test.c main.c 
[taoge@localhost learn_nm]$ gcc test.o main.o
[taoge@localhost learn_nm]$ ./a.out 
rainy days
[taoge@localhost learn_nm]$ nm *

a.out:
08049564 d _DYNAMIC
08049630 d _GLOBAL_OFFSET_TABLE_
0804849c R _IO_stdin_used
         w _Jv_RegisterClasses
08049554 d __CTOR_END__
08049550 d __CTOR_LIST__
0804955c D __DTOR_END__
08049558 d __DTOR_LIST__
0804854c r __FRAME_END__
08049560 d __JCR_END__
08049560 d __JCR_LIST__
0804964c A __bss_start
08049648 D __data_start
08048450 t __do_global_ctors_aux
08048330 t __do_global_dtors_aux
080484a0 R __dso_handle
         w __gmon_start__
0804844a T __i686.get_pc_thunk.bx
08049550 d __init_array_end
08049550 d __init_array_start
080483e0 T __libc_csu_fini
080483f0 T __libc_csu_init
         U __libc_start_main@@GLIBC_2.0
0804964c A _edata
08049654 A _end
0804847c T _fini
08048498 R _fp_hw
08048290 T _init
08048300 T _start
0804964c b completed.5963
08049648 W data_start
08049650 b dtor_idx.5965
08048390 t frame_dummy
080483c8 T main
080483b4 T print
         U puts@@GLIBC_2.0
nm: main.c: File format not recognized

main.o:
00000000 T main
         U print
nm: test.c: File format not recognized
nm: test.h: File format not recognized

test.o:
00000000 T print
         U puts
[taoge@localhost learn_nm]$ 
```
可以看到，对于目标文件和可执行文件而言，均可以获得其中的函数，如print函数。

我们继续看静态库和动态库，如下：
[plain] view plain copy print ?

[taoge@localhost learn_nm]$ ls

main.c  test.c  test.h

[taoge@localhost learn_nm]$ gcc -c test.c

[taoge@localhost learn_nm]$ ar rcs libtest.a test.o

[taoge@localhost learn_nm]$ gcc -shared -fPIC -o libtest.so test.o

[taoge@localhost learn_nm]$ ls

libtest.a  libtest.so  main.c  test.c  test.h  test.o

[taoge@localhost learn_nm]$ nm lib*



libtest.a:



test.o:

00000000 T print

         U puts



libtest.so:

000014bc a _DYNAMIC

00001590 a _GLOBAL_OFFSET_TABLE_

         w _Jv_RegisterClasses

000014a8 d __CTOR_END__

000014a4 d __CTOR_LIST__

000014b0 d __DTOR_END__

000014ac d __DTOR_LIST__

000004a0 r __FRAME_END__

000014b4 d __JCR_END__

000014b4 d __JCR_LIST__

000015a4 A __bss_start

         w __cxa_finalize@@GLIBC_2.1.3

00000440 t __do_global_ctors_aux

00000350 t __do_global_dtors_aux

000014b8 d __dso_handle

         w __gmon_start__

00000419 t __i686.get_pc_thunk.bx

000015a4 A _edata

000015ac A _end

00000478 T _fini

000002ec T _init

000015a4 b completed.5963

000015a8 b dtor_idx.5965

000003e0 t frame_dummy

00000420 T print

         U puts@@GLIBC_2.0

[taoge@localhost learn_nm]$
```
[taoge@localhost learn_nm]$ ls
main.c  test.c  test.h
[taoge@localhost learn_nm]$ gcc -c test.c
[taoge@localhost learn_nm]$ ar rcs libtest.a test.o
[taoge@localhost learn_nm]$ gcc -shared -fPIC -o libtest.so test.o
[taoge@localhost learn_nm]$ ls
libtest.a  libtest.so  main.c  test.c  test.h  test.o
[taoge@localhost learn_nm]$ nm lib*

libtest.a:

test.o:
00000000 T print
         U puts

libtest.so:
000014bc a _DYNAMIC
00001590 a _GLOBAL_OFFSET_TABLE_
         w _Jv_RegisterClasses
000014a8 d __CTOR_END__
000014a4 d __CTOR_LIST__
000014b0 d __DTOR_END__
000014ac d __DTOR_LIST__
000004a0 r __FRAME_END__
000014b4 d __JCR_END__
000014b4 d __JCR_LIST__
000015a4 A __bss_start
         w __cxa_finalize@@GLIBC_2.1.3
00000440 t __do_global_ctors_aux
00000350 t __do_global_dtors_aux
000014b8 d __dso_handle
         w __gmon_start__
00000419 t __i686.get_pc_thunk.bx
000015a4 A _edata
000015ac A _end
00000478 T _fini
000002ec T _init
000015a4 b completed.5963
000015a8 b dtor_idx.5965
000003e0 t frame_dummy
00000420 T print
         U puts@@GLIBC_2.0
[taoge@localhost learn_nm]$ 
```
可以看到，我们可以从静态库和动态库中获取到函数名称，如print函数。

好，我们再来看看全局变量的情形，我们把main.c改为：
[cpp] view plain copy print ?

#include <stdio.h>



int add(int x, int y)

{

    return x + y;

}



int aaa;

int bbb = 1;

char szTest[] = "good";



int main()

{

    int ccc = 2;

    return 0;

}
```
#include <stdio.h>

int add(int x, int y)
{
	return x + y;
}

int aaa;
int bbb = 1;
char szTest[] = "good";

int main()
{
	int ccc = 2;
	return 0;
}
```
然后用nm分析a.out(注意，如果只有nm命令，则默认a.out为其要处理的文件):
[plain] view plain copy print ?

[taoge@localhost learn_nm]$ ls

main.c

[taoge@localhost learn_nm]$ gcc main.c

[taoge@localhost learn_nm]$ ./a.out

[taoge@localhost learn_nm]$ nm a.out

08049538 d _DYNAMIC

08049604 d _GLOBAL_OFFSET_TABLE_

0804847c R _IO_stdin_used

         w _Jv_RegisterClasses

08049528 d __CTOR_END__

08049524 d __CTOR_LIST__

08049530 D __DTOR_END__

0804952c d __DTOR_LIST__

08048520 r __FRAME_END__

08049534 d __JCR_END__

08049534 d __JCR_LIST__

08049628 A __bss_start

08049618 D __data_start

08048430 t __do_global_ctors_aux

08048310 t __do_global_dtors_aux

08048480 R __dso_handle

         w __gmon_start__

0804842a T __i686.get_pc_thunk.bx

08049524 d __init_array_end

08049524 d __init_array_start

080483c0 T __libc_csu_fini

080483d0 T __libc_csu_init

         U __libc_start_main@@GLIBC_2.0

08049628 A _edata

08049634 A _end

0804845c T _fini

08048478 R _fp_hw

08048274 T _init

080482e0 T _start

08049630 B aaa

08048394 T add

0804961c D bbb

08049628 b completed.5963

08049618 W data_start

0804962c b dtor_idx.5965

08048370 t frame_dummy

080483a2 T main

08049620 D szTest

[taoge@localhost learn_nm]$
```
[taoge@localhost learn_nm]$ ls
main.c
[taoge@localhost learn_nm]$ gcc main.c 
[taoge@localhost learn_nm]$ ./a.out 
[taoge@localhost learn_nm]$ nm a.out 
08049538 d _DYNAMIC
08049604 d _GLOBAL_OFFSET_TABLE_
0804847c R _IO_stdin_used
         w _Jv_RegisterClasses
08049528 d __CTOR_END__
08049524 d __CTOR_LIST__
08049530 D __DTOR_END__
0804952c d __DTOR_LIST__
08048520 r __FRAME_END__
08049534 d __JCR_END__
08049534 d __JCR_LIST__
08049628 A __bss_start
08049618 D __data_start
08048430 t __do_global_ctors_aux
08048310 t __do_global_dtors_aux
08048480 R __dso_handle
         w __gmon_start__
0804842a T __i686.get_pc_thunk.bx
08049524 d __init_array_end
08049524 d __init_array_start
080483c0 T __libc_csu_fini
080483d0 T __libc_csu_init
         U __libc_start_main@@GLIBC_2.0
08049628 A _edata
08049634 A _end
0804845c T _fini
08048478 R _fp_hw
08048274 T _init
080482e0 T _start
08049630 B aaa
08048394 T add
0804961c D bbb
08049628 b completed.5963
08049618 W data_start
0804962c b dtor_idx.5965
08048370 t frame_dummy
080483a2 T main
08049620 D szTest
[taoge@localhost learn_nm]$ 
```
可以看到，不仅有add函数，还有全局变量aaa, bbb和szTest, 要注意， aaa是未初始化的，所以在Bss段，而bbb、szTest是初始化了的，所以在Data段。值得注意的是，并没有ccc, 因为ccc是局部变量， nm看不到的。

我们还应该注意到，在上面看不到"good", 为啥呢？因为nm是用来看szTest而非"good"的。别忘了，我们之前介绍过的strings命令可干这事，如下：
[plain] view plain copy print ?

[taoge@localhost learn_nm]$ ls

a.out  main.c

[taoge@localhost learn_nm]$ strings a.out

/lib/ld-linux.so.2

__gmon_start__

libc.so.6

_IO_stdin_used

__libc_start_main

GLIBC_2.0

PTRh

[^_]

good

[taoge@localhost learn_nm]$
```
[taoge@localhost learn_nm]$ ls
a.out  main.c
[taoge@localhost learn_nm]$ strings a.out 
/lib/ld-linux.so.2
__gmon_start__
libc.so.6
_IO_stdin_used
__libc_start_main
GLIBC_2.0
PTRh
[^_]
good
[taoge@localhost learn_nm]$ 
```
nm命令主要列出特性文件中的符号信息，具体更加详细的用法，请问man, 我就不再过多介绍了。
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原文地址：https://www.cnblogs.com/baiduboy/p/6048113.html