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relocate code sections to end up with stage2 starting at 0x500

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Elaina Claus
2024-10-12 22:14:47 -04:00
parent c60bad1066
commit eb97aac673
4 changed files with 42 additions and 36 deletions
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27
src/mbr/mbr.nasm
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@@ -42,16 +42,18 @@ nop
ALIGN 4
init:
cli ; We do not want to be interrupted
cli ; We do not want to be interrupted
xor ax, ax ; 0 AX
mov ds, ax ; Set segment registers to 0
mov ss, ax ; Set Stack Segment to 0
mov sp, EARLY_STACK_START ; Setup stack
mov bp, sp ; base ptr = stack ptr
sub sp, 0x20 ; local varible space
xor ax, ax ; 0 AX
mov ds, ax ; Set segment registers to 0
mov es, ax
mov ss, ax ; Set Stack Segment to 0
mov sp, EARLY_STACK_START ; Setup stack
mov bp, sp ; base ptr = stack ptr
sub sp, 0x10 ; local varible space
xor cx, cx
mov ch, 0x01 ; 256 WORDs in MBR (512 bytes), 0x0100 in cx
mov si, 0x7C00 ; Current MBR Address (loaded here by BIOS)
mov di, MBR_ENTRY ; New MBR Address (our new relocation address)
@@ -115,12 +117,11 @@ main:
mov dword eax, dword [bx + PartEntry_t.lba_start]
push dword eax ; lba
xor ax, ax
push ax ; offset = 0
mov ax, VBR_ENTRY
shr ax, 4
push ax ; segment = 7C0
push ax ; offset = 0x7c00
xor ax, ax
push ax ; segment = 0
; uint8_t read_stage2_raw(uint16_t buf_segment, uint16_t buf_offset,
; uint32_t lba,