pxe_asm.s2.asm_bios_ia32 1.4 KB raw

section .realmode
​
global pxe_call
global set_pxe_fp
​
set_pxe_fp:
    mov eax, [esp + 4]
    mov [pxe_call.pxe_fp], eax
    ret
​
pxe_call:
    ; Save GDT in case BIOS overwrites it
    sgdt [.gdt]
​
    ; Save IDT
    sidt [.idt]
​
    ; Load BIOS IVT
    lidt [.rm_idt]
​
    ; Save non-scratch GPRs
    push ebx
    push esi
    push edi
    push ebp
​
    lea ebp, [esp + 20]
​
    ; Jump to real mode
    jmp 0x08:.bits16
  .bits16:
    bits 16
    mov ax, 0x10
    mov ds, ax
    mov es, ax
    mov fs, ax
    mov gs, ax
    mov ss, ax
    mov eax, cr0
    and al, 0xfe
    mov cr0, eax
    jmp 0x00:.cszero
  .cszero:
    xor ax, ax
    mov ss, ax
    mov ds, ax
    mov es, ax
    mov fs, ax
    mov gs, ax
​
    sti
​
    push word [bp + 4]
    push word [bp + 8]
    push word [bp + 0]
    call far [.pxe_fp]
    add sp, 6
​
    cli
​
    ; Restore GDT
    o32 lgdt [cs:.gdt]
​
    ; Restore IDT
    o32 lidt [cs:.idt]
​
    ; Jump back to pmode
    mov ebx, cr0
    or bl, 1
    mov cr0, ebx
    jmp 0x18:.bits32
  .bits32:
    bits 32
    mov bx, 0x20
    mov ds, bx
    mov es, bx
    mov fs, bx
    mov gs, bx
    mov ss, bx
​
    and eax, 0xffff
​
    ; Restore non-scratch GPRs
    pop ebp
    pop edi
    pop esi
    pop ebx
​
    ; Exit
    ret
​
align 16
  .pxe_fp:   dd 0
  .gdt:      dq 0
  .idt:      dq 0
  .rm_idt:   dw 0x3ff
             dd 0
​
section .note.GNU-stack noalloc noexec nowrite progbits

tab: 2 4 8 wrap: off on

1	section .realmode
2
3	global pxe_call
4	global set_pxe_fp
5
6	set_pxe_fp:
7	mov eax, [esp + 4]
8	mov [pxe_call.pxe_fp], eax
9	ret
10
11	pxe_call:
12	; Save GDT in case BIOS overwrites it
13	sgdt [.gdt]
14
15	; Save IDT
16	sidt [.idt]
17
18	; Load BIOS IVT
19	lidt [.rm_idt]
20
21	; Save non-scratch GPRs
22	push ebx
23	push esi
24	push edi
25	push ebp
26
27	lea ebp, [esp + 20]
28
29	; Jump to real mode
30	jmp 0x08:.bits16
31	.bits16:
32	bits 16
33	mov ax, 0x10
34	mov ds, ax
35	mov es, ax
36	mov fs, ax
37	mov gs, ax
38	mov ss, ax
39	mov eax, cr0
40	and al, 0xfe
41	mov cr0, eax
42	jmp 0x00:.cszero
43	.cszero:
44	xor ax, ax
45	mov ss, ax
46	mov ds, ax
47	mov es, ax
48	mov fs, ax
49	mov gs, ax
50
51	sti
52
53	push word [bp + 4]
54	push word [bp + 8]
55	push word [bp + 0]
56	call far [.pxe_fp]
57	add sp, 6
58
59	cli
60
61	; Restore GDT
62	o32 lgdt [cs:.gdt]
63
64	; Restore IDT
65	o32 lidt [cs:.idt]
66
67	; Jump back to pmode
68	mov ebx, cr0
69	or bl, 1
70	mov cr0, ebx
71	jmp 0x18:.bits32
72	.bits32:
73	bits 32
74	mov bx, 0x20
75	mov ds, bx
76	mov es, bx
77	mov fs, bx
78	mov gs, bx
79	mov ss, bx
80
81	and eax, 0xffff
82
83	; Restore non-scratch GPRs
84	pop ebp
85	pop edi
86	pop esi
87	pop ebx
88
89	; Exit
90	ret
91
92	align 16
93	.pxe_fp: dd 0
94	.gdt: dq 0
95	.idt: dq 0
96	.rm_idt: dw 0x3ff
97	dd 0
98
99	section .note.GNU-stack noalloc noexec nowrite progbits