source: bootcd/isolinux/syslinux-6.03/efi/x86_64/linux.S

/* ----------------------------------------------------------------------- *
 *
 *   Copyright 2013 Intel Corporation; author: Matt Fleming
 *
 *   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, Inc., 51 Franklin St, Fifth Floor,
 *   Boston MA 02110-1301, USA; either version 2 of the License, or
 *   (at your option) any later version; incorporated herein by reference.
 *
 * ----------------------------------------------------------------------- */

#define CR0_PG_FLAG     0x80000000
#define MSR_EFER        0xc0000080

        .globl kernel_jump
        .type kernel_jump,@function
        .code64
kernel_jump:
        cli

        /*
         * Setup our segment selector (0x10) and return address (%rdi)
         * on the stack in preparation for the far return below.
         */
        mov     $0x1000000000, %rcx
        addq    %rcx, %rdi
        pushq   %rdi

        .code32
pm_code:

        /* Disable IA-32e mode by clearing IA32_EFER.LME */
        xorl    %eax, %eax
        xorl    %edx, %edx
        movl    $MSR_EFER, %ecx
        wrmsr

        /* Turn off paging to disable long mode */
        movl    %cr0, %eax
        andl    $~CR0_PG_FLAG, %eax
        movl    %eax, %cr0

        /* Far return */
        lret

        .code64
        .align 4
        .globl efi_handover_32
        .type  efi_handover_32,@function
efi_handover_32:
        movl    $38, errno(%rip)        /* ENOSYS */
        ret

        .globl efi_handover_64
        .globl efi_handover
        .type  efi_handover_64,@function
        .type  efi_handover,@function
efi_handover_64:
efi_handover:
        add     $512, %rcx
        cli
        jmp     *%rcx