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more rtfm'ing with encoding, 25 bytes of free code space in vbr now

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Elaina Claus
2025-09-09 18:37:39 -04:00
parent 0d90b3efd6
commit 3c654b1be0
1 changed files with 17 additions and 29 deletions
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46
src/vbr/vbr.nasm
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@@ -72,7 +72,7 @@ init:
cld
rep stosb
sub sp, 0x20 ; local varible space (32 bytes)
sub sp, 0x10 ; local varible space (32 bytes)
push bp
sti ; all done with inital setup and relocation, reenable interupts
@@ -100,23 +100,17 @@ main:
mov word [bp - 4], si ; part_offset
mov word [bp - 6], bx ; partition_table
.load_fs_data:
mov ax, PartTable_t_size ; count=
push ax
mov ax, [bp - 6] ; src= ptr partition_table
push ax
mov ax, partition_table ; dst=
push ax
call kmemcpy ; copy partition table data
.load_fs_data:
push PartTable_t_size ; count=
push word [bp - 6] ; src= ptr partition_table
push partition_table ; dst=
call kmemcpy ; copy partition table data to bss
add sp, 0x6
mov ax, (FAT32_bpb_t_size + FAT32_ebpb_t_size) ; size in byte, should be 90 bytes
push ax
mov ax, __ENTRY
push ax
mov ax, fat32_bpb ;
push ax
call kmemcpy ; copy bpb & ebpb to memory
push (FAT32_bpb_t_size + FAT32_ebpb_t_size) ; size in byte, should be 90 bytes
push __ENTRY ; src
push fat32_bpb ; dst
call kmemcpy ; copy bpb & ebpb to bss
add sp, 0x6
.check_FAT_size: ; we only support a very specific setup of FAT32
@@ -129,17 +123,13 @@ main:
movzx ax, byte [bp - 2]
push ax ; drive_num
mov ax, STAGE2_SECTOR_COUNT
push ax ; count
push STAGE2_SECTOR_COUNT ; count
mov dword eax, 0x1
push dword eax ; lba
mov ax, STAGE2_ENTRY
push ax ; offset
xor ax, ax
push ax ; segment = 0
push STAGE2_ENTRY ; offset
push 0x00 ; segment = 0
; uint8_t read_stage2_raw(uint16_t buf_segment, uint16_t buf_offset,
; uint32_t lba,
@@ -166,6 +156,7 @@ times (510 - ($ - $$)) nop ; Fill the rest of sector with nop
BootSig:
dw 0xAA55 ; Add boot signature at the end of bootloader
; !!! END VBR !!!
section .bss follows=.text
begin_bss:
@@ -177,14 +168,11 @@ align 16, resb 1
fat32_bpb resb FAT32_bpb_t_size
fat32_ebpb resb FAT32_ebpb_t_size
align 16, resb 1
fat32_nc_data resb 16
align 16, resb 1
lba_packet resb LBAPkt_t_size
align 512, resb 1
stack_bottom resb 512 ; 512b stack early on
stack_bottom resb (512 - 16) ; 512b stack early on
stack_top:
vbr_redzone resb 32
vbr_redzone resb 16
end_bss: