use long mode, x86_64-unknown-none works now

2 files changed, 176 insertions, 122 deletions

diff --git a/asm/boot.asm b/asm/boot.asm
index bb852ef..29e807c 100644
--- a/asm/boot.asm
+++ b/asm/boot.asm
@@ -3,156 +3,210 @@
 ; 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 0x7C00] ; address where bootloader is loaded
+[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 ss, ax
-mov sp, 0x7C00
-
-mov ah, 0x0E
-mov al, 'R'
-int 0x10
-mov al, 'e'
-int 0x10
-mov al, 'a'
-int 0x10
-mov al, 'l'
-int 0x10
-mov al, 0x0D
-int 0x10
-mov al, 0x0A
-int 0x10
-mov al, 0x00 ; stops serial and bios output from overlapping in qemu -nographic
-int 0x10     ; output
+mov fs, ax
+mov gs, ax
+cld
 
 ; activate a20
-mov ax, 0x2401
-int 0x15
-jc error
+mov ax, A20_LINE_ENABLE
+int BIOS_INT_MEMORY_OP
+jc error_a20_line
+mov si, msg_a20_line
+call print
 
-; load kernel
-; 'docs' from https://www.ctyme.com/intr/rb-0607.htm
-mov ah, 0x02
-mov al, 1 ; number of sectors to read (must be nonzero)
-mov ch, 0 ; low eight bits of cylinder number
-mov cl, 2 ; sector number 1-63 (bits 0-5); high two bits of cylinder (bits 6-7,
-          ; hard disk only)
-mov dh, 0 ; head number
-; dl is already set by bios
-mov bx, 0x1000 ; data buffer
+; 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
-int 0x13 ; read disk
-jc error
 
-; load gdt
-lgdt [gdt_descriptor]
+; read disk
+mov ah, 0x02
+int BIOS_INT_DISK_OP
+jc error_disk_read
+mov si, msg_disk_read
+call print
 
-; jump to pm
-cli
-mov eax, cr0
-or eax, 1
-mov cr0, eax
-jmp 0x08:pm_start
+; zero es
+push ax
+xor ax, ax
+mov es, ax
+pop ax
 
-error:
-  mov al, 'e'
-  int 0x10
-  mov al, 'r'
-  int 0x10
-  mov al, 'r'
-  int 0x10
-  mov al, 'o'
-  int 0x10
-  mov al, 'r'
-  int 0x10
-  jmp $
+mov edi, PAGE_TABLE_LOAD_ADDR
+jmp lm_load
 
-gdt_data:
-  ; null segment
-  dq 0x0000000000000000
-  ; code segment
-  dw 0xFFFF
-  dw 0x0000
+; 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
 
-  db 0x00
-  db 10011010b ; 32-bit code segment, present, ring 0
-  db 11001111b ; limit bits 16-19
-  db 0x00
+  ; PDPT0E0
+  lea eax, [es:di + 2 * PAGE_TABLE_SIZE]
+  or eax, 11b
+  mov [es:di + PAGE_TABLE_SIZE], eax
 
-  ; data segment
-  dw 0xFFFF
-  dw 0x0000
+  ; PDT0E0
+  lea eax, [es:di + 3 * PAGE_TABLE_SIZE]
+  or eax, 11b
+  mov [es:di + 2 * PAGE_TABLE_SIZE], eax
 
-  db 0x00
-  db 10010010b ; 32-bit data segment, present, ring 0
-  db 11001111b ; limit bits 16-19
-  db 0x00
+  ; 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 32]
+[bits 64]
 
-; entry point
-pm_start:
-  ; data segment registers
+; long mode entry
+lm_start:
   mov ax, 0x10
   mov ds, ax
   mov es, ax
   mov fs, ax
   mov gs, ax
   mov ss, ax
-  mov esp, 0x80000
 
-  ; TODO actually configure COM1
-  mov dx, 0x3F8 ; COM1
-  mov al, 'P'
-  out dx, al
-  mov al, 'r'
-  out dx, al
-  mov al, 'o'
-  out dx, al
-  mov al, 't'
-  out dx, al
-  mov al, 'e'
-  out dx, al
-  mov al, 'c'
-  out dx, al
-  mov al, 't'
-  out dx, al
-  mov al, 'e'
-  out dx, al
-  mov al, 'd'
-  out dx, al
-  mov al, 0x0D
-  out dx, al
-  mov al, 0x0A
-  out dx, al
+  ; set up serial device
+  ; TODO poll and whatnot (in rust??)
+  mov dx, 0x3F8
+
+  jmp KERNEL_LOAD_ADDR_ES * 0x10
 
-  jmp 0x08:0x10000
+msg_a20_line db "a20 line", 0x0D, 0x0A, 0x00
+msg_disk_read db "disk read", 0x0D, 0x0A, 0x00
 
-pm_error:
-  mov al, 'p'
-  out dx, al
-  mov al, 'm'
-  out dx, al
-  mov al, 'e'
-  out dx, al
-  mov al, 'r'
-  out dx, al
-  mov al, 'r'
-  out dx, al
-  mov al, 'o'
-  out dx, al
-  mov al, 'r'
-  out dx, al
-  jmp $
-  
 times 510-($-$$) db 0 ; 2 bytes less now
 db 0x55
 db 0xAA
diff --git a/asm/kernel.asm b/asm/kernel.asm
index 23c0d5d..b4cbb30 100644
--- a/asm/kernel.asm
+++ b/asm/kernel.asm
@@ -1,4 +1,4 @@
-[bits 32]
+[bits 64]
 
 mov al, 'K'
 out dx, al
@@ -18,6 +18,6 @@ mov al, 0x0A
 out dx, al
 mov al, 0x00
 out dx, al
-jmp $
-
-times 512-($-$$) db 0
+.done
+  hlt
+  jmp .done