text: #ifndef _X86_DEBUG_H
  #define _X86_DEBUG_H
  
  // void (*debug_putchar) (char ch);
  // 
  // Note: this mean you define "debug_putchar" variable in the head file;
  // When other file include this file like "#include<arch/debug.h>", it will
  // define many times,I think if your compile let it go through because the 
  // version is old, GCC-10.0.1 get an error: Multiple definitions.
  // so I put the define "debug_putchar" to "src/arch/x86/mach-i386/debug.c".
  //
  //
  // And put a "extern" in "src/kernel/debug.c" because just one func "printk" reference
  // the "debug_putchar" (i just find)
  
  void init_kernel_debug();
  void debug_putchar(char ch);
  
  #endif  /* _X86_DEBUG_H */
  