real.s2.asm_bios_ia32 2.4 KB raw

section .realmode
​
global rm_hcf
rm_hcf:
    ; Load BIOS IVT
    lidt [.rm_idt]
​
    ; 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
    btr ax, 0
    mov cr0, eax
    jmp 0x00:.cszero
  .cszero:
    xor ax, ax
    mov ds, ax
    mov es, ax
    mov fs, ax
    mov gs, ax
    mov ss, ax
​
    sti
  .hang:
    hlt
    jmp .hang
    bits 32
​
  .rm_idt:   dw 0x3ff
             dd 0
​
global rm_int
rm_int:
    ; Self-modifying code: int $int_no
    mov al, byte [esp+4]
    mov byte [.int_no], al
​
    ; Save out_regs
    mov eax, dword [esp+8]
    mov dword [.out_regs], eax
​
    ; Save in_regs
    mov eax, dword [esp+12]
    mov dword [.in_regs], eax
​
    ; 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
​
    ; 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
​
    ; Load in_regs
    mov dword [ss:.esp], esp
    mov esp, dword [ss:.in_regs]
    pop gs
    pop fs
    pop es
    pop ds
    popfd
    pop ebp
    pop edi
    pop esi
    pop edx
    pop ecx
    pop ebx
    pop eax
    mov esp, dword [ss:.esp]
​
    sti
​
    ; Indirect interrupt call
    db 0xcd
  .int_no:
    db 0
​
    cli
​
    ; Load out_regs
    mov dword [ss:.esp], esp
    mov esp, dword [ss:.out_regs]
    lea esp, [esp + 10*4]
    push eax
    push ebx
    push ecx
    push edx
    push esi
    push edi
    push ebp
    pushfd
    push ds
    push es
    push fs
    push gs
    mov esp, dword [ss:.esp]
​
    ; Restore GDT
    o32 lgdt [ss:.gdt]
​
    ; Restore IDT
    o32 lidt [ss:.idt]
​
    ; Jump back to pmode
    mov eax, cr0
    or al, 1
    mov cr0, eax
    jmp 0x18:.bits32
  .bits32:
    bits 32
    mov ax, 0x20
    mov ds, ax
    mov es, ax
    mov fs, ax
    mov gs, ax
    mov ss, ax
​
    ; Restore non-scratch GPRs
    pop ebp
    pop edi
    pop esi
    pop ebx
​
    ; Exit
    ret
​
align 16
  .esp:      dd 0
  .out_regs: dd 0
  .in_regs:  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 rm_hcf
4	rm_hcf:
5	; Load BIOS IVT
6	lidt [.rm_idt]
7
8	; Jump to real mode
9	jmp 0x08:.bits16
10	.bits16:
11	bits 16
12	mov ax, 0x10
13	mov ds, ax
14	mov es, ax
15	mov fs, ax
16	mov gs, ax
17	mov ss, ax
18	mov eax, cr0
19	btr ax, 0
20	mov cr0, eax
21	jmp 0x00:.cszero
22	.cszero:
23	xor ax, ax
24	mov ds, ax
25	mov es, ax
26	mov fs, ax
27	mov gs, ax
28	mov ss, ax
29
30	sti
31	.hang:
32	hlt
33	jmp .hang
34	bits 32
35
36	.rm_idt: dw 0x3ff
37	dd 0
38
39	global rm_int
40	rm_int:
41	; Self-modifying code: int $int_no
42	mov al, byte [esp+4]
43	mov byte [.int_no], al
44
45	; Save out_regs
46	mov eax, dword [esp+8]
47	mov dword [.out_regs], eax
48
49	; Save in_regs
50	mov eax, dword [esp+12]
51	mov dword [.in_regs], eax
52
53	; Save GDT in case BIOS overwrites it
54	sgdt [.gdt]
55
56	; Save IDT
57	sidt [.idt]
58
59	; Load BIOS IVT
60	lidt [.rm_idt]
61
62	; Save non-scratch GPRs
63	push ebx
64	push esi
65	push edi
66	push ebp
67
68	; Jump to real mode
69	jmp 0x08:.bits16
70	.bits16:
71	bits 16
72	mov ax, 0x10
73	mov ds, ax
74	mov es, ax
75	mov fs, ax
76	mov gs, ax
77	mov ss, ax
78	mov eax, cr0
79	and al, 0xfe
80	mov cr0, eax
81	jmp 0x00:.cszero
82	.cszero:
83	xor ax, ax
84	mov ss, ax
85
86	; Load in_regs
87	mov dword [ss:.esp], esp
88	mov esp, dword [ss:.in_regs]
89	pop gs
90	pop fs
91	pop es
92	pop ds
93	popfd
94	pop ebp
95	pop edi
96	pop esi
97	pop edx
98	pop ecx
99	pop ebx
100	pop eax
101	mov esp, dword [ss:.esp]
102
103	sti
104
105	; Indirect interrupt call
106	db 0xcd
107	.int_no:
108	db 0
109
110	cli
111
112	; Load out_regs
113	mov dword [ss:.esp], esp
114	mov esp, dword [ss:.out_regs]
115	lea esp, [esp + 10*4]
116	push eax
117	push ebx
118	push ecx
119	push edx
120	push esi
121	push edi
122	push ebp
123	pushfd
124	push ds
125	push es
126	push fs
127	push gs
128	mov esp, dword [ss:.esp]
129
130	; Restore GDT
131	o32 lgdt [ss:.gdt]
132
133	; Restore IDT
134	o32 lidt [ss:.idt]
135
136	; Jump back to pmode
137	mov eax, cr0
138	or al, 1
139	mov cr0, eax
140	jmp 0x18:.bits32
141	.bits32:
142	bits 32
143	mov ax, 0x20
144	mov ds, ax
145	mov es, ax
146	mov fs, ax
147	mov gs, ax
148	mov ss, ax
149
150	; Restore non-scratch GPRs
151	pop ebp
152	pop edi
153	pop esi
154	pop ebx
155
156	; Exit
157	ret
158
159	align 16
160	.esp: dd 0
161	.out_regs: dd 0
162	.in_regs: dd 0
163	.gdt: dq 0
164	.idt: dq 0
165	.rm_idt: dw 0x3ff
166	dd 0
167
168	section .note.GNU-stack noalloc noexec nowrite progbits