System.map file is a symbol table used by the kernel

背景

System.map文件中包含了符号以及对应的在内存中的地址表信息.  
例如  
[root@db-172-16-3-150 ~]# less /boot/System.map-$(uname -r)  
[root@db-172-16-3-150 ~]# uname -r  
2.6.32-358.el6.x86_64  
[root@db-172-16-3-150 ~]# less /boot/System.map-2.6.32-358.el6.x86_64  
0000000000000000 A VDSO32_PRELINK  
0000000000000000 D __per_cpu_start  
0000000000000000 D per_cpu__irq_stack_union  
0000000000000000 A xen_irq_disable_direct_reloc  
0000000000000000 A xen_save_fl_direct_reloc  
0000000000000040 A VDSO32_vsyscall_eh_frame_size  
... 略  
中间的字段代表符号类型信息, 第一个字段是内存地址, 第三个字段是符号名 :   
类型如下 :   
Some of these types are:  
A for absolute.  
B or b for uninitialized data section (called BSS).  
D or d for initialized data section.  
G or g for initialized data section for small objects (global).  
i for sections specific to DLLs.  
N for debugging symbol.  
p for stack unwind section.  
R or r for read only data section.  
S or s for uninitialzed data section for small objects.  
T or t for text (code) section.  
U for undefined.  
V or v for weak object.  
W or w for weak objects which have not been tagged so.  
- for stabs symbol in an a.out object file.  
? for 'symbol type unknown.'  
  
在其他机器使用stap产生的ko文件时, 如果对方的System.map文件与主文件不一致, 则可能无法使用tapset中的symname()函数通过地址得到符号名.  

http://blog.163.com/digoal@126/blog/static/163877040201391451459751/

System.map文件可以在以下两个位置找到.  
 /usr/src/kernels/`uname -r`/.config  
 /lib/modules/`uname -r`/build/System.map  
[root@db-172-16-3-150 commands]# md5sum /lib/modules/2.6.32-358.el6.x86_64/build/System.map  
ef58493777cfca95c66aab2028d771a0  /lib/modules/2.6.32-358.el6.x86_64/build/System.map  
[root@db-172-16-3-150 commands]# md5sum /boot/System.map-2.6.32-358.el6.x86_64   
ef58493777cfca95c66aab2028d771a0  /boot/System.map-2.6.32-358.el6.x86_64  
  
符号表更多的信息可参考http://en.wikipedia.org/wiki/Symbol_table  
  
[其他]  
内核自动产生的make config,   
/usr/src/kernels/2.6.32-358.el6.x86_64/.config  
#  
# Automatically generated make config: don't edit  
# Linux kernel version: 2.6.32-358.el6.x86_64  
# Fri Feb 22 00:26:01 2013  
#  
CONFIG_64BIT=y  
# CONFIG_X86_32 is not set  
CONFIG_X86_64=y  
CONFIG_X86=y  
CONFIG_OUTPUT_FORMAT="elf64-x86-64"  
CONFIG_ARCH_DEFCONFIG="arch/x86/configs/x86_64_defconfig"  
CONFIG_GENERIC_CMOS_UPDATE=y  
CONFIG_CLOCKSOURCE_WATCHDOG=y  
CONFIG_GENERIC_CLOCKEVENTS=y  
CONFIG_GENERIC_CLOCKEVENTS_BROADCAST=y  
CONFIG_LOCKDEP_SUPPORT=y  
CONFIG_STACKTRACE_SUPPORT=y  
CONFIG_HAVE_LATENCYTOP_SUPPORT=y  
CONFIG_MMU=y  
CONFIG_ZONE_DMA=y  
CONFIG_NEED_DMA_MAP_STATE=y  
...  

参考

1. http://en.wikipedia.org/wiki/System.map

2. http://en.wikipedia.org/wiki/Kernel_oops

3. http://en.wikipedia.org/wiki/Kernel_panic

4. https://sourceware.org/systemtap/SystemTap_Beginners_Guide/useful-systemtap-scripts.html

5. http://en.wikipedia.org/wiki/Symbol_table

6. https://sourceware.org/systemtap/tapsets/API-symname.html

7. /usr/src/kernels/uname -r/.config

8. /lib/modules/uname -r/build/System.map

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