source: bootcd/isolinux/syslinux-6.03/gpxe/src/arch/i386/firmware/pcbios/fakee820.c

/* Copyright (C) 2008 Michael Brown <mbrown@fensystems.co.uk>.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

FILE_LICENCE ( GPL2_OR_LATER );

#include <realmode.h>
#include <biosint.h>

/** Assembly routine in inline asm */
extern void int15_fakee820();

/** Original INT 15 handler */
static struct segoff __text16 ( real_int15_vector );
#define real_int15_vector __use_text16 ( real_int15_vector )

/** An INT 15,e820 memory map entry */
struct e820_entry {
        /** Start of region */
        uint64_t start;
        /** Length of region */
        uint64_t len;
        /** Type of region */
        uint32_t type;
} __attribute__ (( packed ));

#define E820_TYPE_RAM           1 /**< Normal memory */
#define E820_TYPE_RSVD          2 /**< Reserved and unavailable */
#define E820_TYPE_ACPI          3 /**< ACPI reclaim memory */
#define E820_TYPE_NVS           4 /**< ACPI NVS memory */

/** Fake e820 map */
static struct e820_entry __text16_array ( e820map, [] ) __used = {
        { 0x00000000ULL, ( 0x000a0000ULL - 0x00000000ULL ), E820_TYPE_RAM },
        { 0x00100000ULL, ( 0xcfb50000ULL - 0x00100000ULL ), E820_TYPE_RAM },
        { 0xcfb50000ULL, ( 0xcfb64000ULL - 0xcfb50000ULL ), E820_TYPE_RSVD },
        { 0xcfb64000ULL, ( 0xcfb66000ULL - 0xcfb64000ULL ), E820_TYPE_RSVD },
        { 0xcfb66000ULL, ( 0xcfb85c00ULL - 0xcfb66000ULL ), E820_TYPE_ACPI },
        { 0xcfb85c00ULL, ( 0xd0000000ULL - 0xcfb85c00ULL ), E820_TYPE_RSVD },
        { 0xe0000000ULL, ( 0xf0000000ULL - 0xe0000000ULL ), E820_TYPE_RSVD },
        { 0xfe000000ULL, (0x100000000ULL - 0xfe000000ULL ), E820_TYPE_RSVD },
        {0x100000000ULL, (0x230000000ULL -0x100000000ULL ), E820_TYPE_RAM },
};
#define e820map __use_text16 ( e820map )

void fake_e820 ( void ) {
        __asm__ __volatile__ (
                TEXT16_CODE ( "\nint15_fakee820:\n\t"
                              "pushfw\n\t"
                              "cmpl $0xe820, %%eax\n\t"
                              "jne 99f\n\t"
                              "cmpl $0x534d4150, %%edx\n\t"
                              "jne 99f\n\t"
                              "pushaw\n\t"
                              "movw %%sp, %%bp\n\t"
                              "andb $~0x01, 22(%%bp)\n\t" /* Clear return CF */
                              "leaw e820map(%%bx), %%si\n\t"
                              "cs rep movsb\n\t"
                              "popaw\n\t"
                              "movl %%edx, %%eax\n\t"
                              "addl $20, %%ebx\n\t"
                              "cmpl %0, %%ebx\n\t"
                              "jne 1f\n\t"
                              "xorl %%ebx,%%ebx\n\t"
                              "\n1:\n\t"
                              "popfw\n\t"
                              "iret\n\t"
                              "\n99:\n\t"
                              "popfw\n\t"
                              "ljmp *%%cs:real_int15_vector\n\t" )
                : : "i" ( sizeof ( e820map ) ) );

        hook_bios_interrupt ( 0x15, ( unsigned int ) int15_fakee820,
                              &real_int15_vector );
}

void unfake_e820 ( void ) {
        unhook_bios_interrupt ( 0x15, ( unsigned int ) int15_fakee820,
                                &real_int15_vector );
}