System.map详解

system.map内容格式为：线性地址类型符号

具体内容如下：
00100000 A phys_startup_32
c0100000 T startup_32
c0100000 A _text                             注:表示内核代码第一个字节的地址
c01000c6 t checkCPUtype
c0100147 t is486

...

c02f97b0 T __kprobes_text_end
c02f9abe t iret_exc
c02fa1af A _etext                              注:内核代码结束的位置，之后为内核初始化的数据
c02fa1b0 A __start___ex_table
c02facc0 A __stop___ex_table
c02fb000 r __func__.12
c02fb000 A __start_rodata
c02fb00c r __func__.13
c02fb020 r __func__.2
c02fb02c r __func__.3
c02fb040 R linux_banner
...

c03e1b28 D net_statistics
c03e1b30 d fn_hash_kmem
c03e1b34 d fn_alias_kmem
c03e1b38 d xfrm_dst_cache
c03e1b3c d secpath_cachep
c03e1b40 A _edata                       注:内核初始化数据结束，之后为未初始化数据
c03e2000 D init_thread_union
c03e4000 A __init_begin
c03e4000 t no_halt
c03e4000 T _sinittext
...

c043a068 b acqseq_lock.5
c043a068 A __bss_stop
c043a068 A _end                         注:内核未初始化数据结束
c043b000 A pg0
ffffe400 A __kernel_vsyscall
ffffe410 A SYSENTER_RETURN
ffffe420 A __kernel_sigreturn
ffffe440 A __kernel_rt_sigreturn

符号类型解析

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.