more of bootloader, tiny kernel stub

1 files changed, 165 insertions, 48 deletions

diff --git a/src/bootloader.asm b/src/bootloader.asm
index e8ab91b..08d1daf 100644
--- a/src/bootloader.asm
+++ b/src/bootloader.asm
@@ -17,20 +17,22 @@
 
 pointers:
 .fat equ 0x0500
+.root_dir equ 0x0504
+.kernel equ 0x0508
 
 fat_header:
 .oem_name            equ 0x7c03;mkfs.fat    - ignored
 .bytes_per_sector    equ 0x7c0b;0x0200      - assumed
 .sectors_per_cluster equ 0x7c0d;0x01        - assumed
-.reserved_sectors    equ 0x7c0e;0x0002      - other values handled
+.reserved_sectors    equ 0x7c0e;0x0004      - other values handled
 .n_fats              equ 0x7c10;0x01        - assumed
-.directory_entries   equ 0x7c11;            -
+.root_dir_entries    equ 0x7c11;            -
 .n_sectors           equ 0x7c13;0x0b40      -
 .media_type          equ 0x7c15;            -
 .sectors_per_fat     equ 0x7c16;            - handled
 .sectors_per_track   equ 0x7c18;0x0012      -
 .sides               equ 0x7c1a;0x0002      -
-.hidden_sectors      equ 0x7c1c;0x0000_0000 - assumed
+.hidden_sectors      equ 0x7c1c;0x0000_0000 - assumed, top half used as scratch for sector number of cluster 0
 .long_sectors        equ 0x7c20;0x0000_0000 - assumed
 .drive_number        equ 0x7c24;            - ignored, used as scratch
 .flags               equ 0x7c25;            - ignored
@@ -148,13 +150,165 @@ memory:
   jne halt
 
   mov ax, word [fat_header.sectors_per_fat]
+  xor ecx, ecx
+  mov cx, word [fat_header.reserved_sectors]
+
+  call allocate_and_load
+
+  mov dword [pointers.fat], ebx
+
+  mov ax, word [fat_header.root_dir_entries]
+  dec ax
+  shr ax, 4
+  inc ax
+
+  xor ecx, ecx
+  mov cx, word [fat_header.reserved_sectors]
+  add cx, word [fat_header.sectors_per_fat]
+  jnc .no_carry
+  or ecx, 0x0001_0000
+.no_carry:
+
+  call allocate_and_load
+
+  mov dword [pointers.root_dir], ebx
+
+  xor edx, edx
+  mov dx, word [fat_header.root_dir_entries]
+  shl edx, 5
+  add edx, ebx
+
+find_kernel:
+  mov eax, 0x6e_72_65_6b;kern
+  mov ecx, 0x20_20_6c_65;el
+  mov ebx, dword [pointers.root_dir]
+
+.loop:
+  test dword [ebx], eax
+  jne .next
+  test dword [ebx + 4], ecx
+  jne .next
+  test word [ebx + 8], 0x79_73;sy
+  jne .next
+  test byte [ebx + 10], 0x73;s
+  je .found
+
+.next:
+  add ebx, 32
+  test ebx, edx
+  jne .loop
+  jmp halt
+
+.found:
+  mov byte [allocate_and_load.load], 0xc3;ret
+
+  mov eax, dword [ebx + 0x1c]
+  dec eax
+  shr eax, 9
+  inc eax
+
+  test eax, 0xffff_0000
+  jnz halt
+
+  push word [ebx + 0x1a]
+
+  call allocate_and_load
+
+  mov dword [pointers.kernel], ebx
+
+  mov ax, word [fat_header.root_dir_entries]
+  dec ax
+  shr ax, 4
+  dec ax
+  add ax, word [fat_header.reserved_sectors]
+  jc halt
+  add ax, word [fat_header.sectors_per_fat]
+  jc halt
+  mov word [fat_header.hidden_sectors + 2], ax
+
+load_kernel:
+  mov word [dap.length], 0x0001
+  mov word [dap.offset], bx
+  xor bx, bx
+  shr ebx, 4
+  test ebx, 0xffff_0000
+  jnz halt
+  mov word [dap.segment], bx
+
+  xor edx, edx
+  pop dx
+  mov word [dap.start + 2], 0x0000
+  mov ah, 0x42
+  mov si, dap
+.loop:
+  mov cx, dx
+  add cx, word [fat_header.hidden_sectors + 2]
+  jc halt
+
+  mov word [dap.start], cx
+
+  int 0x13
+
+  mov ebx, dword [pointers.fat]
+  add ebx, edx
+  add ebx, edx
+  add ebx, edx
+
+  xor edx, edx
+  mov dx, word [ebx + 1]
+  shl edx, 8
+  mov dl, byte [ebx]
+
+  add word [dap.segment], 0x0020
+  jc halt
+
+  mov ecx, edx
+  and ecx, 0x0ff8
+  test ecx, 0x0ff8
+  jne .loop
+
+  mov ebx, dword [pointers.kernel]
+
+  ;Parse kernel executable header,
+  ;Go through relocation tables,
+  ;Get kernel_start.
+
+  cli
+
+  lgdt [gdt]
+  mov eax, cr0
+  or al, 0x01
+  mov cr0, eax
+  jmp 0x08:kernel_start;get start from file header
+
+gdt:
+dw 0x28
+dd gdt + 6
+dq 0x0000_0000_0000_0000
+dq 0x0040_9a00_0000_7fff;0x000000 - 0x007fff
+dq 0x0040_9200_0000_7fff
+dq 0x00c0_9a00_8000_0ff7;0x008000 - 0xffffff
+dq 0x00c0_9200_8000_0ff7
+
+dap:
+dw 0x0010
+.length  dw 0x0003
+.offset  dw 0x7e00
+.segment dw 0x0000
+.start   dd 0x0000_0001
+.start_h dd 0x0000_0000
+
+;ecx = sector
+;ax = sector count
+;bx out = address of start
+allocate_and_load:
   mov word [dap.length], ax
+  mov dword [dap.start], ecx
 
   dec ax
   shr ax, 3
   inc ax
 
-fat_allocate:
   mov bx, 0x200e
   xor cx, cx
   mov dx, 0x2200
@@ -189,50 +343,17 @@ fat_allocate:
   and ebx, 0x0000_dfff
   shl ebx, 12
 
-  mov dword [pointers.fat], ebx
-
-  mov dl, byte [fat_header.drive_number]
-  mov ax, word [fat_header.reserved_sectors]
-  mov word [dap.start], ax
-  mov word [dap.offset], bx
-  shr ebx, 16
-  and bx, 0xf000
-  mov word [dap.segment], bx
+.load:
+  mov eax, ebx
+  mov word [dap.offset], ax
+  shr eax, 4
+  and ax, 0xf000
+  mov word [dap.segment], ax
 
   mov ah, 0x42
   mov si, dap
-  int 0x15
-
-  mov ebx, dword [pointers.fat]
-
-  ;fat loaded - load kernel
-
-  cli
-
-  lgdt [gdt]
-  mov eax, cr0
-  or al, 0x01
-  mov cr0, eax
-  jmp 0x08:pmode
-
-gdt:
-dw 0x28
-dd gdt + 6
-dq 0x0000_0000_0000_0000
-dq 0x0040_9a00_0000_7fff;0x000000 - 0x007fff
-dq 0x0040_9200_0000_7fff
-dq 0x00c0_9a00_8000_0ff7;0x008000 - 0xffffff
-dq 0x00c0_9200_8000_0ff7
-
-dap:
-dw 0x0010
-.length dw 0x0001
-.offset dw 0x7e00
-.segment dw 0x0000
-.start dq 1
+  int 0x13
 
-allocate:
-  ;TODO
   ret
 
 halt:
@@ -240,7 +361,3 @@ halt:
 .hlt:
   hlt
   jmp .hlt
-
-bits 32
-pmode:
-