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

DEFINITIONS

1. get_bios_ebda
2. get_bios_ebda_length
3. check_for_bios_corruption
4. start_periodic_check_for_corruption

#ifndef _ASM_X86_BIOS_EBDA_H
#define _ASM_X86_BIOS_EBDA_H

#include <asm/io.h>

/*
 * Returns physical address of EBDA.  Returns 0 if there is no EBDA.
 */
static inline unsigned int get_bios_ebda(void)
{
        /*
         * There is a real-mode segmented pointer pointing to the
         * 4K EBDA area at 0x40E.
         */
        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 */