Kernel의 printk debug-1

1. Linux Kernel Debug 설정

linux kernel 의 config 설정과 관련된 부분

2. Linux Print 관련 Debug 

관련내용
  https://elinux.org/Debugging_by_printing

• Kernel Config 설정확인 

$ cd linux
$ vi .config   

#
# printk and dmesg options
#
CONFIG_PRINTK_TIME=y                    //  printk의 time 정보  
CONFIG_MESSAGE_LOGLEVEL_DEFAULT=4       //  Log Level 설정  
# CONFIG_BOOT_PRINTK_DELAY is not set
# CONFIG_DYNAMIC_DEBUG is not set

Name	String	Meaning	alias function
KERN_EMERG	"0"	Emergency messages, system is about to crash or is unstable	pr_emerg
KERN_ALERT	"1"	Something bad happened and action must be taken immediately	pr_alert
KERN_CRIT	"2"	A critical condition occurred like a serious hardware/software failure	pr_emerg
KERN_ERR	"3"	An error condition, often used by drivers to indicate difficulties with the hardware	pr_crit
KERN_WARNING	"4"	A warning, meaning nothing serious by itself but might indicate problems	pr_err
KERN_NOTICE	"5"	Nothing serious, but notably nevertheless. Often used to report security events.	pr_notice
KERN_INFO	"6"	Informational message e.g. startup information at driver initialization	pr_info
KERN_DEBUG	"7"	Debug messages	pr_debug
KERN_DEFAULT	"d"	The default kernel loglevel
KERN_CONT	""	"continued" line of log printout	pr_cont

아래와 같이 printk로 각각 debug 가능

printk(KERN_NOTICE "Kernel command line: %s\n", boot_command_line); 

• 초기의 디버깅 

Kernel Boot 초기에 Print가 Serial 설정 및 초기화 문제로 아래와 같이 설정을 해줘야한다.
추후 필요 없다면 삭제

CONFIG_EARLY_PRINTK=y
CONFIG_DEBUG_KERNEL=y

Kernel Hacking-> Kernel low-level debugging functions

  http://forum.falinux.com/zbxe/index.php?mid=lecture_tip&page=82&document_srl=519453

• 별도의 각각의 Device의 Debug가 필요하다면 설정 

ALSA Debug

CONFIG_SND_VERBOSE_PRINTK
CONFIG_SND_DEBUG

  https://cateee.net/lkddb/web-lkddb/SND_DEBUG.html


2.1 User에서 Kernel Message 설정 및 확인 

일반적인 Kernel Debug방법이며, printk를 이용하여 쉽게 debug가 가능하며, dmesg를 이용하여 boot time 역시 쉽게 알수 있다.

• User에서 Kernel printk 설정 

$ cat /proc/sys/kernel/printk
7 4 1 3
current default minimum boot-time-default

$ sudo -s

$ echo 3 > /proc/sys/kernel/printk

$ cat /proc/sys/kernel/printk   // current 만 변경 
3 4 1 3

$ echo "7 4 1 7" > /proc/sys/kernel/printk

$ cat /proc/sys/kernel/printk  // reboot 되면 원래 설정으로 돌아감 
7 4 1 7

$ dmesg   // kernel message 확인 

  https://www.kernel.org/doc/Documentation/
  https://www.kernel.org/doc/Documentation/kernel-parameters.txt