add kernel stuff, idt, welcome message

asm/boot.asm

@@ -12,6 +12,13 @@ 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
@@ -42,7 +49,7 @@ cld
 ; activate a20
 mov ax, A20_LINE_ENABLE
 int BIOS_INT_MEMORY_OP
-jc error_a20_line
+jc error
 mov si, msg_a20_line
 call print
 
@@ -59,7 +66,7 @@ xor bx, bx
 ; read disk
 mov ah, 0x02
 int BIOS_INT_DISK_OP
-jc error_disk_read
+jc error
 mov si, msg_disk_read
 call print
 
@@ -143,17 +150,11 @@ lm_load:
 
   jmp 0x08:lm_start
 
-error_a20_line:
+error:
   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
+  .msg db "err ", 0x00
+  ret
 
 done:
   hlt
@@ -172,11 +173,6 @@ print:
     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
@@ -201,11 +197,89 @@ lm_start:
   ; 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 read", 0x0D, 0x0A, 0x00
+msg_disk_read db "disk", 0x0D, 0x0A, 0x00
 
 times 510-($-$$) db 0 ; 2 bytes less now
 db 0x55