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added 2 proc's to read mbr/vbr to a buffer and setup some early ptr's to partition tables and the like

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This commit is contained in:
Elaina Claus
2025-09-12 23:16:04 -04:00
parent 40fa4062ce
commit 7cd6baa74d
1 changed files with 91 additions and 53 deletions
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142
src/stage2/stage2.nasm
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@@ -36,18 +36,10 @@
section .text
begin_text:
; dl = byte boot_drive
; ax = word part_offset (active partition offset)
; si = ptr PartTable_t partition_table
; di = ptr FAT32_bpb_t fat32_bpb
ALIGN 4, db 0x90
init:
cli ; We do not want to be interrupted
; these 4 are stored in the .data section and are effectivly const types
mov [vbr_part_table_ptr], si ; pointer to partition_table
mov [vbr_fat32_bpb_ptr], di ; pointer to fat32_bpb
mov [boot_drive], dl ; copy boot_drive to globals
mov [partition_offset], ax ; copy partition_offset to globals
mov [boot_drive], dl ; copy boot_drive to globals
mov ax, __STAGE2_SEGMENT ; set all our segments to the configured segment, except es
mov ds, ax ; *
@@ -129,22 +121,34 @@ main:
je main.stage2_main
ERROR STAGE2_SIGNATURE_MISSING
.stage2_main:
; copy partition table data to .data section in stage2
__CDECL16_CALL_ARGS partition_table, word [vbr_part_table_ptr], PartTable_t_size
__CDECL16_CALL kmemcpy, 3
; copy bpb & ebpb to memory
__CDECL16_CALL_ARGS fat32_bpb, word [vbr_fat32_bpb_ptr], (FAT32_bpb_t_size + FAT32_ebpb_t_size)
__CDECL16_CALL kmemcpy, 3
call SetTextMode
call disable_cursor_bios
; setup the early heap
__CDECL16_CALL_ARGS early_heap_state
__CDECL16_CALL arena_init, 1
__CDECL16_CALL_ARGS HelloPrompt_info
__CDECL16_CALL PrintString, 1
; setup the early heap
__CDECL16_CALL_ARGS early_heap_state
; setup and store our vbr/mbr (e)bpb
__CDECL16_CALL_ARGS 0x200, 0x10
__CDECL16_CALL arena_alloc, 2
mov word [mbr_ptr], ax
push ax ; dst
movzx ax, byte [boot_drive]
push ax ; boot_drive
__CDECL16_CALL read_mbr, 2 ; fill mbr buffer
__CDECL16_CALL_ARGS 0x200, 0x10
__CDECL16_CALL arena_alloc, 2
mov word [vbr_ptr], ax
push ax ; dst
movzx ax, byte [boot_drive]
push ax ; boot_drive
__CDECL16_CALL read_vbr, 2 ; fill vbr buffer
; enable A20 gate
call EnableA20
@@ -197,55 +201,80 @@ hcf:
; destination buffer needs 512 bytes of space
read_mbr:
__CDECL16_PROC_ENTRY
.func:
__BOCHS_MAGIC_DEBUG
.proc:
; read mbr on boot drive to memory (for the partition table)
movzx ax, byte [bp - 4]
movzx ax, byte [bp + 4]
push ax ; drive_num (2)
push 0x01 ; count (2)
push dword 0x0 ; lba (4)
push word [bp - 6] ; offset = dst
push word [bp + 6] ; offset = dst
push __STAGE2_SEGMENT ; this segment
__CDECL16_CALL read_disk_raw, 12
call read_disk_raw
add sp, 0xC
.check_sig:
mov bx, [bp + 6]
cmp word [bx + 0x1FE], 0xAA55 ; check for bytes at end
jne read_mbr.error
; TODO: this needs error checking, zero checking, check the sig a bunch of stuff...
.endf:
.update_globals:
mov ax, [bp + 6]
add ax, 0x1B8 ; offset to start of PartTable
mov [part_table_ptr], ax
.endp:
__CDECL16_PROC_EXIT
ret
.error:
ERROR STEVIA_DEBUG_ERR
; int read_vbr(int boot_drive, void* mbr, void* buf)
; int read_vbr(int boot_drive, void* buf)
read_vbr:
__CDECL16_PROC_ENTRY
.func:
.proc:
__BOCHS_MAGIC_DEBUG
; read vbr on boot partition to memory (for fat bpb/ebpb)
.calc_part_offset:
mov bx, [bp - 6]
add bx, 0x1B8 ; offset to partition table in mbr
mov cx, 4 ; only checking 4 entries
mov bx, word [part_table_ptr] ; base pointer @ partition table
mov cx, 4 ; only checking 4 entries
mov si, PartEntry_t.attributes
.find_active_L0:
mov al, byte [bx + PartEntry_t.attributes]
mov al, byte [bx + si]
test al, 0x80 ; 0x80 == 1000_0000b
jnz read_vbr.active_found
add bx, 0x10 ; add 16 bytes to offset
je read_vbr.active_found
add si, 0x10 ; add 16 bytes to offset (next part entry's attributes)
loop read_vbr.find_active_L0
jmp read_vbr.error
.active_found:
movzx ax, byte [bp - 4]
add bx, si ; update base to active part
movzx ax, byte [bp + 4]
push ax ; drive_num (2)
push 0x01 ; count (2)
mov eax, dword [bx + PartEntry_t.lba_start]
push dword eax ; lba (4)
push word [bp - 6] ; offset = dst
push word [bp + 6] ; offset = dst
push __STAGE2_SEGMENT ; this segment
__CDECL16_CALL read_disk_raw, 12
call read_disk_raw
add sp, 0xC
; vbr (with fat bpb/ebpb) is at the buffer now
.endf:
.check_sig:
mov bx, [bp + 6]
cmp word [bx + 0x1FE], 0xAA55 ; check for bytes at end
jne read_mbr.error
.check_FAT_size:
test word [bx + FAT32_bpb_t.unused2_ZERO_word], 0 ; TotSectors16 will not be set if FAT32
jnz read_vbr.error
.update_globals:
mov word [fat32_bpb_ptr], bx
add bx, FAT32_bpb_t_size ; offset to ebpb
mov word [fat32_ebpb_ptr], bx
.endp:
__CDECL16_PROC_EXIT
ret
.error:
ERROR STEVIA_DEBUG_ERR
@@ -386,25 +415,14 @@ BootTarget:
db 'BOOT BIN'
;
; pre-bss init globals (generally const...but there are exceptions)
; pre-bss init globals
;
align 8, db 0
; set to boot_drive passed from BIOS almost first thing in init
align 4, db 0
boot_drive:
db 0x00
align 8, db 0
partition_offset:
dw 0x0000
align 8, db 0
vbr_fat32_bpb_ptr:
dw 0x0000
align 8, db 0
vbr_part_table_ptr:
dw 0x0000
align 16, db 0
IntToHex_table:
db '0123456789ABCDEF'
@@ -497,8 +515,28 @@ STAGE2_SIG: dd 0xDEADBEEF ; Signature to mark the end of the stag
section .bss follows=.sign
begin_bss:
; structures
align 4, resb 1
mbr_ptr:
resw 1
align 4, resb 1
vbr_ptr:
resw 1
align 4, resb 1
part_table_ptr:
resw 1
align 4, resb 1
fat32_bpb_ptr:
resw 1
align 4, resb 1
fat32_ebpb_ptr:
resw 1
; structures
align 16, resb 1
partition_table:
resb PartTable_t_size