/*      $OpenBSD: run_i386.S,v 1.3 2022/12/08 01:25:44 guenther Exp $   */

/*
 * Copyright (c) 2015 YASUOKA Masahiko <yasuoka@yasuoka.net>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <machine/asm.h>
#include <machine/specialreg.h>

#define CODE_SEGMENT    0x10
#define DATA_SEGMENT    0x18

        .globl run_i386_size
run_i386_size:
        .long run_i386_end - run_i386_start

        .align  4
        .text
        .globl  run_i386_start
run_i386_start:
start:
        /*
         * run_i386(_start) is to call the loaded kernel's start() with
         * 32bit segment mode from x64 mode.
         * %rdi == loaded start address, %rsi == kernel start address
         */

        /* re-arrange the parameters for the x86 calling convention */
        mov     %edx, (run_i386_end - start - 0x20)(%rdi)
        mov     %ecx, (run_i386_end - start - 0x1c)(%rdi)
        mov     %r8d, (run_i386_end - start - 0x18)(%rdi)
        mov     %r9d, (run_i386_end - start - 0x14)(%rdi)
        mov     0x8(%rsp), %edx
        mov     %edx, (run_i386_end - start - 0x10)(%rdi)
        mov     0x10(%rsp), %edx
        mov     %edx, (run_i386_end - start - 0xc)(%rdi)
        mov     0x18(%rsp), %edx
        mov     %edx, (run_i386_end - start - 0x8)(%rdi)
        mov     0x20(%rsp), %edx
        mov     %edx, (run_i386_end - start - 0x4)(%rdi)

        /* Prepare jump address */
        lea     (start32a - start)(%rdi), %rax
        movl    %eax, (start32r - start)(%rdi)

        cli

        /* Setup GDT */
        lea     (gdt - start)(%rdi), %rax
        mov     %rax, (gdtrr - start)(%rdi)
        lgdt    (gdtr - start)(%rdi)

        /* Jump to set %cs */
        ljmp    *(start32r - start)(%rdi)

        .align  4
start32a:
        .code32
        movl    $DATA_SEGMENT, %eax
        movl    %eax, %ds
        movl    %eax, %es
        movl    %eax, %fs
        movl    %eax, %gs
        movl    %eax, %ss

        lea     (run_i386_end - start - 0x20)(%edi), %eax
        mov     %eax, %esp

        /* Disable Paging in CR0 */
        movl    %cr0, %eax
        andl    $(~CR0_PG), %eax
        movl    %eax, %cr0

        /* Disable PAE in CR4 */
        movl    %cr4, %eax
        andl    $(~CR4_PAE), %eax
        movl    %eax, %cr4

        jmp     start32b
start32b:
        .code32

        call    *%esi

        .align  4
start32r:
        .long   0
        .long   CODE_SEGMENT
        .align  4
gdt:
        .long   0, 0
        .long   0, 0
        .byte   0xff, 0xff, 0x00, 0x00, 0x00, 0x9f, 0xcf, 0x00
        .byte   0xff, 0xff, 0x00, 0x00, 0x00, 0x93, 0xcf, 0x00
gdtr:
        .word   gdtr - gdt
gdtrr:
        .quad
start32end:
        /* Space for the stack */
        .align  4
        .space  8192
run_i386_end: