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more error codes and checks in vbr

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This commit is contained in:
Elaina Claus
2025-09-18 14:07:45 -04:00
parent f87f88a0dc
commit 11656c2827
2 changed files with 49 additions and 32 deletions
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50
src/stage2/stage2.nasm
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@@ -230,17 +230,27 @@ ReadVbrData:
mov ax, word [bx + SteviaInfoStruct_t.p16_MbrPtr]
add ax, DISK_PARTITION_TABLE_OFFSET
mov bx, ax ; offset to part table
mov cx, 4 ; only checking 4 entries
mov si, PartEntry_t.attributes
.find_active_L0:
mov al, byte [bx + si]
test al, 0x80 ; 0x80 == 1000_0000b
je ReadVbrData.active_found
mov al, [bx + PartEntry_t.attributes]
cmp al, 0x80 ; 0x80 == 1000_0000b
je ReadVbrData.check_fstype
add bx, PartEntry_t_size ; next part entry's attributes
loop ReadVbrData.find_active_L0
jmp ReadVbrData.error_noactive
.active_found:
.check_fstype:
; check for part_type = 0x0C (DOS 7.1+/W95 FAT32 w/ LBA) or 0x1C (Hidden 0x0C)
__BOCHS_MAGIC_DEBUG
mov al, [bx + PartEntry_t.part_type]
cmp al, 0x0C
je ReadVbrData.active_ok
; *or*
cmp al, 0x1C
je ReadVbrData.active_ok
jmp ReadVbrData.error_badparttype ; error if part_type != 0x1C or 0x0C
.active_ok:
movzx ax, byte [bp + 4]
push ax ; drive_num (2)
push 0x01 ; count (2)
@@ -259,23 +269,31 @@ ReadVbrData:
jne ReadVbrData.error_nosign
.check_FAT_sanity:
; we only quickly validate that this is *probably* a FAT32 volume
test word [bx + FAT32_bpb_t.u16_TotalSectors16], 0 ; TotalSectors16 should be 0 (use TotalSectors32 in bpb)
jnz ReadVbrData.error_badfatfs
test word [bx + FAT32_bpb_t.u16_FATSize16], 0 ; FatSize16 will be 0 if FAT32 (use FATSize32 in ebpb)
jnz ReadVbrData.error_badfatfs
add bx, 11 ; point bx at start of bpb (skip jmp code and ident)
cmp word [bx + FAT32_bpb_t.u16_TotalSectors16], 0 ; TotalSectors16 should be 0 (use TotalSectors32 in bpb)
jne ReadVbrData.error_totsectors
test word [bx + FAT32_bpb_t.u16_RootEntryCount16], 0 ; root dir info is in data clusters on fat32
jnz ReadVbrData.error_badfatfs
cmp word [bx + FAT32_bpb_t.u16_FATSize16], 0 ; FatSize16 will be 0 if FAT32 (use FATSize32 in ebpb)
jne ReadVbrData.error_fatsz
cmp word [bx + FAT32_bpb_t.u16_RootEntryCount16], 0 ; root dir info is in data clusters on fat32
jne ReadVbrData.error_rootdir
.endp:
__CDECL16_PROC_EXIT
ret
.error_noactive:
ERROR STAGE2_ERROR_BAD_VBR
ERROR STAGE2_VBR_E_ACTIVE
.error_nosign:
ERROR STAGE2_ERROR_BAD_VBR
.error_badfatfs:
ERROR STAGE2_ERROR_BAD_VBR
ERROR STAGE2_VBR_E_SIGN
.error_totsectors:
ERROR STAGE2_VBR_E_TOT
.error_fatsz:
ERROR STAGE2_VBR_E_FATSZ
.error_rootdir:
ERROR STAGE2_VBR_E_DIRENT
.error_badparttype:
ERROR STAGE2_VBR_E_PARTTYPE
; set ds and es segments back to the base of the loader
%ifnmacro __TINY_DS_ES