#include <linux/kernel.h>
  #include <linux/crash_dump.h>
  #include <linux/init.h>
  #include <linux/errno.h>

  #include <linux/export.h>

  
  /*
   * If we have booted due to a crash, max_pfn will be a very low value. We need
   * to know the amount of memory that the previous kernel used.
   */
  unsigned long saved_max_pfn;
  
  /*
   * stores the physical address of elf header of crash image
   *
   * Note: elfcorehdr_addr is not just limited to vmcore. It is also used by
   * is_kdump_kernel() to determine if we are booting after a panic. Hence put
   * it under CONFIG_CRASH_DUMP and not CONFIG_PROC_VMCORE.
   */
  unsigned long long elfcorehdr_addr = ELFCORE_ADDR_MAX;

  EXPORT_SYMBOL_GPL(elfcorehdr_addr);

  
  /*

   * stores the size of elf header of crash image
   */
  unsigned long long elfcorehdr_size;
  
  /*

   * elfcorehdr= specifies the location of elf core header stored by the crashed
   * kernel. This option will be passed by kexec loader to the capture kernel.

   *
   * Syntax: elfcorehdr=[size[KMG]@]offset[KMG]

   */
  static int __init setup_elfcorehdr(char *arg)
  {
  	char *end;
  	if (!arg)
  		return -EINVAL;
  	elfcorehdr_addr = memparse(arg, &end);

  	if (*end == '@') {
  		elfcorehdr_size = elfcorehdr_addr;
  		elfcorehdr_addr = memparse(end + 1, &end);
  	}

  	return end > arg ? 0 : -EINVAL;
  }
  early_param("elfcorehdr", setup_elfcorehdr);