1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
|
; bootler
; legacy bootloader in nasm-flavoured asm
; 2026 Andromeda
; GPL licensed
LOAD_ADDR equ 0x7C00
KERNEL_START equ 2 ; first sector on disk to load kernel from; 1 indexed
KERNEL_SIZE equ 1 ; length of kernel in sectors
KERNEL_LOAD_ADDR_ES equ 0x1000 ; kernel to be loaded at es * 0x10 + 0x0000
PAGE_TABLE_LOAD_ADDR equ 0x1000 ; start of page table; 4 * pt size
PAGE_TABLE_SIZE equ 0x1000 ; size of page table in bytes
A20_LINE_ENABLE equ 0x2401 ; magic number in ax to enable a20 line with 0x15
BIOS_INT_DISK_OP equ 0x13
BIOS_INT_MEMORY_OP equ 0x15
CR0_PE equ 1 << 0 ; Protected Mode Enabled
CR0_PG equ 1 << 31 ; Paging
CR4_PAE equ 1 << 5 ; Physical Address Extension
CR4_PGE equ 1 << 7 ; Page Global Enabled
MSR_IA32_EFER equ 0xC0000080 ; Extended Feature Enable model-specific Register
[bits 16]
[org LOAD_ADDR]
jmp 0x0000:.cs_reset ; in case it loads us at 0x7C00:0x0000
.cs_reset:
xor ax, ax
mov ss, ax
mov sp, LOAD_ADDR ; stack builds down, loader faces up
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
cld
; activate a20
mov ax, A20_LINE_ENABLE
int BIOS_INT_MEMORY_OP
jc error_a20_line
mov si, msg_a20_line
call print
; prep to read disk
mov al, KERNEL_SIZE ; size in sectors, min. 1
mov ch, 0 ; cylinder
mov cl, KERNEL_START ; start sector, 1-indexed
mov dh, 0 ; head
; dl set by bios
mov bx, KERNEL_LOAD_ADDR_ES ; load addr es:bx
mov es, bx
xor bx, bx
; read disk
mov ah, 0x02
int BIOS_INT_DISK_OP
jc error_disk_read
mov si, msg_disk_read
call print
; zero es
push ax
xor ax, ax
mov es, ax
pop ax
mov edi, PAGE_TABLE_LOAD_ADDR
jmp lm_load
; expects:
; es:edi -> 16kb for page table
; ss:esp -> stack
; heavily based on https://wiki.osdev.org/Entering_Long_Mode_Directly
lm_load:
; clear page table
push di
mov ecx, PAGE_TABLE_SIZE
xor eax, eax
cld
rep stosd ; clear space for all 4 tables
pop di
; PML4TE0
lea eax, [es:di + PAGE_TABLE_SIZE]
or eax, 11b
mov [es:di], eax
; PDPT0E0
lea eax, [es:di + 2 * PAGE_TABLE_SIZE]
or eax, 11b
mov [es:di + PAGE_TABLE_SIZE], eax
; PDT0E0
lea eax, [es:di + 3 * PAGE_TABLE_SIZE]
or eax, 11b
mov [es:di + 2 * PAGE_TABLE_SIZE], eax
; PT0
push di
lea di, [di + 3 * PAGE_TABLE_SIZE]
mov eax, 0x11
.set_pt_entry
mov [es:di], eax
add eax, 0x1000
add di, 8
cmp eax, 0x200000 ; size of page
jb .set_pt_entry
pop di
; disable interrupts from PIC by masking all interrupts
mov al, 0xFF ; mask
out 0xA1, al
out 0x21, al
; PAE, PGE
mov eax, CR4_PAE | CR4_PGE
mov cr4, eax
; cr3 -> PML4TE0
mov edx, edi
mov cr3, edx
; highs LME bit in EFER
mov ecx, MSR_IA32_EFER
rdmsr
or eax, 0x00000100
wrmsr
; activate long mode
mov ebx, cr0
or ebx, CR0_PG | CR0_PE
mov cr0, ebx
cli
lgdt [gdt_descriptor]
jmp 0x08:lm_start
error_a20_line:
mov si, .msg
call print
jmp done
.msg db "err a20 line", 0x00
error_disk_read:
mov si, .msg
call print
jmp done
.msg db "err disk read", 0x00
done:
hlt
jmp done
print:
pushad
.loop
lodsb
test al, al
je .done
mov ah, 0x0E
int 0x10
jmp .loop
.done
popad
ret
; TODO make real idt
empty_idt:
dw 0 ; length
dd 0 ; base
; TODO make readable (yoinked from https://wiki.osdev.org/Entering_Long_Mode_Directly)
gdt_data:
dq 0x0000000000000000
dq 0x00209A0000000000
dq 0x0000920000000000
gdt_descriptor:
dw $ - gdt_data - 1 ; size
dd gdt_data ; start
[bits 64]
; long mode entry
lm_start:
mov ax, 0x10
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
mov ss, ax
; set up serial device
; TODO poll and whatnot (in rust??)
mov dx, 0x3F8
jmp KERNEL_LOAD_ADDR_ES * 0x10
msg_a20_line db "a20 line", 0x0D, 0x0A, 0x00
msg_disk_read db "disk read", 0x0D, 0x0A, 0x00
times 510-($-$$) db 0 ; 2 bytes less now
db 0x55
db 0xAA
|
