linux/arch/x86/include/asm/bios_ebda.h

#ifndef _ASM_X86_BIOS_EBDA_H
#define _ASM_X86_BIOS_EBDA_H

#include <asm/io.h>

/*
 * there is a real-mode segmented pointer pointing to the
 * 4K EBDA area at 0x40E.
 */
static inline unsigned int get_bios_ebda(void)
{
	unsigned int address = *(unsigned short *)phys_to_virt(0x40E);
	address <<= 4;
	return address;	/* 0 means none */
}

/*
 * Return the sanitized length of the EBDA in bytes, if it exists.
 */
static inline unsigned int get_bios_ebda_length(void)
{
	unsigned int address;
	unsigned int length;

	address = get_bios_ebda();
	if (!address)
		return 0;

	/* EBDA length is byte 0 of the EBDA (stored in KiB) */
	length = *(unsigned char *)phys_to_virt(address);
	length <<= 10;

	/* Trim the length if it extends beyond 640KiB */
	length = min_t(unsigned int, (640 * 1024) - address, length);
	return length;
}

void reserve_ebda_region(void);

#ifdef CONFIG_X86_CHECK_BIOS_CORRUPTION
/*
 * This is obviously not a great place for this, but we want to be
 * able to scatter it around anywhere in the kernel.
 */
void check_for_bios_corruption(void);
void start_periodic_check_for_corruption(void);
#else
static inline void check_for_bios_corruption(void)
{
}

static inline void start_periodic_check_for_corruption(void)
{
}
#endif

#endif /* _ASM_X86_BIOS_EBDA_H */