linux内核模块编程2

1. /proc/kallsyms列出了linux内核导出的所有符号及对应的地址。

基本格式是： 逻辑地址   标识  符号（内核导出的符号），如00100000 A phys_startup_32

标识分为A、T、t、W、R、D等，分别意义如下：

c0100000 A _text              注:表示内核代码第一个字节的地址

c02fa1af A _etext      注:内核代码结束的位置，之后为内核初始化的数据

c03e1b40 A _edata       注:内核初始化数据结束，之后为未初始化数据

c043a068 A _end                         注:内核未初始化数据结束

标识说明：

小写字母表示局部; 大写字母表示全局(外部).
A
The symbol's value is absolute, and will not be changed by further linking.

B
The symbol is in the uninitialized data section (known as BSS).

C
The symbol is common. Common symbols are uninitialized data. When linking, multiple common symbols may appear with the same name. If the symbol is defined anywhere, the common symbols are treated as undefined references. For more details on common symbols, see the discussion of -warn-common in Linker options.

D
The symbol is in the initialized data section.

G
The symbol is in an initialized data section for small objects. Some object file formats permit more efficient access to small data objects, such as a global int variable as opposed to a large global array.

I
The symbol is an indirect reference to another symbol. This is a GNU extension to the a.out object file format which is rarely used.

N
The symbol is a debugging symbol.

R
The symbol is in a read only data section.

S
The symbol is in an uninitialized data section for small objects.

T
The symbol is in the text (code) section.

U
The symbol is undefined.

V
The symbol is a weak object. When a weak defined symbol is linked with a normal defined symbol, the normal defined symbol is used with no error. When a weak undefined symbol is linked and the symbol is not defined, the value of the weak symbol becomes zero with no error.

W
The symbol is a weak symbol that has not been specifically tagged as a weak object symbol. When a weak defined symbol is linked with a normal defined symbol, the normal defined symbol is used with no error. When a weak undefined symbol is linked and the symbol is not defined, the value of the weak symbol becomes zero with no error.

-
The symbol is a stabs symbol in an a.out object file. In this case, the next values printed are the stabs other field, the stabs desc field, and the stab type. Stabs symbols are used to hold debugging information. For more information, see Stabs.

?
The symbol type is unknown, or object file format specific. 
  

2. 如果没有/proc/kallsyms，可以借助编译内核是生成的system.map（在/usr/src/linux中，使用nm /boot/vmlinux-2.4.7-10 > System.map）中的符号，然后使用unsigned long kallsyms_lookup_name(const char *)寻找指定符号的逻辑地址。头文件好像是