bunch of stuff idek

1 files changed, 286 insertions, 0 deletions

diff --git a/bootler/asm/boot.asm b/bootler/asm/boot.asm
new file mode 100644
index 0000000..5291d58
--- /dev/null
+++ b/bootler/asm/boot.asm
@@ -0,0 +1,286 @@
+; 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
+
+; 64 bit IDT stuff
+IDT_ADDR equ 0x8000 ; bottom of IDT
+IDT_SIZE equ 0x1000 ; size of IDT
+
+IDT_SEGMENT equ 0x0008       ; gdt code segment to jump to for idt calls
+
+; magic numbers and things
+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
+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
+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:
+  mov si, .msg
+  call print
+  .msg db "err ", 0x00
+  ret
+
+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 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
+  
+  ; qemu -no-graphic overlaps serial and bios output without this
+  mov al, 0x0D
+  out dx, al
+  mov al, 0x0A
+  out dx, al
+
+  ; initialize IDT at IDT_ADDR
+  call idt_init
+
+  int3 ; silly test
+
+  jmp KERNEL_LOAD_ADDR_ES * 0x10
+
+idt_init:
+  ; clear space for idt
+  mov rdi, IDT_ADDR
+  push di
+  mov rcx, IDT_SIZE / 4
+  xor rax, rax
+  cld
+  rep stosd ; clear double word for each rcx
+  pop di
+
+  push rdx ; dx contains the output device
+           ; nothing between here and the `pop rdx` will be able to print
+
+  ; breakpoint
+  mov rdi, 0x8E ; present, no dpl, interrupt
+  mov rsi, 0x03 ; breakpoint interrupt
+  lea rdx, [int_hdl_dummy]
+  call mk_idt_entry
+
+  pop rdx ; get back dx output device
+
+  lidt [idt_descriptor]
+
+  ret
+
+int_hdl_dummy:
+  mov rsi, .msg
+  call lm_print
+  iretq
+  .msg db "INTdummy", 0x0D, 0x0A, 0x00
+
+; rdi =  flags
+; rsi =  entry number
+; rdx -> handler
+mk_idt_entry:
+  mov rax, rdx
+  mov rcx, rsi
+
+  shl rcx, 4 ; offset = entry number * 16
+  add rcx, IDT_ADDR
+
+  mov word [rcx + 0], ax          ; offset
+  mov word [rcx + 2], IDT_SEGMENT ; code segment
+  mov word [rcx + 5], di
+  mov byte [rcx + 4], 0           ; IST (0 = none)
+  shr rax, 16
+  mov word [rcx + 6], ax          ; offset
+  shr rax, 16
+  mov dword [rcx + 8], eax        ; offset
+  mov dword [rcx + 12], 0         ; reserved
+  ret
+
+lm_print:
+  .loop
+    mov al, [rsi]
+    test al, al
+    jz .done
+    out dx, al
+    inc si
+    jmp .loop
+  .done:
+    ret
+
+idt_descriptor:
+  dw IDT_SIZE - 1 ; size
+  dq IDT_ADDR     ; start
+
+msg_a20_line db "a20 line", 0x0D, 0x0A, 0x00
+msg_disk_read db "disk", 0x0D, 0x0A, 0x00
+
+times 510-($-$$) db 0 ; 2 bytes less now
+db 0x55
+db 0xAA