doubts regarding the kernel programs

[Dhananjaya hiremath]

Hello sir,
          Here we got the kernel source code and we want to modify the code so that we can print a some debug message.If we do this change where we will see this modification if we compile this again or is there any mothod to see weather modified method is correct or not.
   
   
  Thank U and 
  Dhananjaya Hiremath

       
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