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more fat fs type checks

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This commit is contained in:
Elaina Claus
2025-09-18 11:50:27 -04:00
parent d8a89cfd2b
commit 8002d1cb54
2 changed files with 12 additions and 5 deletions
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11
src/stage2/stage2.nasm
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@@ -257,8 +257,15 @@ ReadVbrData:
mov bx, [bp + 6]
cmp word [bx + 0x1FE], 0xAA55 ; check for bytes at end
jne ReadVbrData.error_nosign
.check_FAT_size:
test word [bx + FAT32_bpb_t.u16_TotalSectors16], 0 ; TotSectors16 will not be set if FAT32
.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
test word [bx + FAT32_bpb_t.u16_RootEntryCount16], 0 ; root dir info is in data clusters on fat32
jnz ReadVbrData.error_badfatfs
.endp:
__CDECL16_PROC_EXIT