2007-06-12 14:32:06     how to see kernel debug message

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2007-06-12 14:32:06     how to see kernel debug message

James Pruett (UNITED STATES)

Message: 36247    Hi,

 

I want to see detailed debug messages, eg  pr_debug("hi");

Q: How do I turn that on?

 

Here are my settings

 

In u-boot:

bf537> printenv bootargs

bootargs=root=/dev/mtdblock0 rw console=ttyBF0,57600 debug loglevel=7

 

During boot I see:

Kernel command line: root=/dev/mtdblock0 rw console=ttyBF0,57600 debug loglevel=7

 

But I never see output from for example:

pr_debug("restoring spi ctl \n" )

 

thanks for any leads.

jp

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2007-06-12 14:46:25     Re: how to see kernel debug message

Mike Frysinger (UNITED STATES)

Message: 36248    pr_debug() isnt actually compiled into the kernel unless you have #define DEBUG at the top of your file

 

once you've booted, just run `dmesg` to see the full buffer

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2007-06-12 14:53:54     Re: how to see kernel debug message

James Pruett (UNITED STATES)

Message: 36249    thanks

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2008-03-13 10:06:34     Re: how to see kernel debug message

murti iki (GERMANY)

Message: 52457    Hello I am wondering if there is an overhead size difference between printk and pr_debug or are they actually the same thing.

One more question would be about displaying these messages. Below I wrote a short hello module but after compiling it and loading it, I can not see the "does it write" message in the output of dmesg command.

 

What am I doing wrong?

thanks alot

murti

 

#include <linux/init.h>

#include <linux/module.h>

#include <linux/kernel.h>

 

#define DEBUG

 

static int __init mymod_init(void) {

  printk(KERN_INFO "Hello, my module\n");

  pr_debug("does it write");

  return 0;

                   }

 

static void __exit mymod_exit(void) {

  printk(KERN_INFO "goodbye my module\n");

                                    }

 

 

module_init(mymod_init);

module_exit(mymod_exit);

 

MODULE_LICENSE("GPL");

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2008-03-13 13:08:20     Re: how to see kernel debug message

Mike Frysinger (UNITED STATES)

Message: 52462    you didnt put DEBUG at the top of the file, so it wasnt used by any of the headers

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2008-03-14 03:37:34     Re: how to see kernel debug message

murti iki (GERMANY)

Message: 52504    Thanks a lot for your help, it seems that I need to review how the C preprocessor  works before going further

About the other question, can you also tell me if  pr_debug is actually a printk or

does it use another mechanism with less overhead?

 

cheers

murti

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2008-03-14 04:58:54     Re: how to see kernel debug message

Yi Li (CHINA)

Message: 52524    if looking at include/linux/kernel.h for pr_debug() definition, things would be clear.

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2008-03-14 06:17:02     Re: how to see kernel debug message

murti iki (GERMANY)

Message: 52530    thanks Yi,

It's clear now.

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