remove shortjmp and ident from bpb

include/fat32/fat32_structures.inc

@@ -58,16 +58,14 @@
 ;                           resulting in a value which does not fit in the Number of Sectors entry at 0x13. 
 
 struc FAT32_bpb_t
-    .reserved_jmpboot        resb 3
     .u16_BytesPerSector      resw 1
-    .ident                   resb 8
     .u8_SectorsPerCluster    resb 1
     .u16_ReservedSectors     resw 1
     .u8_FatCount             resb 1
-    .u16_unused1_ZERO        resb 2      ; Root entry count field, 0 on fat32
+    .u16_RootEntryCount16    resw 1      ; Root dir entry count field, 0 on fat32
-    .u16_unused2_ZERO        resb 2      ; total sectors size 16, 0 on fat32
+    .u16_TotalSectors16      resw 1      ; total number of sectors size, 0 on fat32
     .u8_MediaDesc            resb 1
-    .u16_unused3_ZERO        resb 2      ; FAT size 16, 0 on fat32
+    .u16_FatSize16           resw 1      ; FAT size 16, 0 on fat32
     .u16_SectorsPerTrack     resw 1
     .u16_HeadCount           resw 1
     .u32_HiddenSectors       resd 1
@@ -91,17 +89,17 @@ endstruc
 ;   8 	System identifier string. Always "FAT32   ". The spec says never to trust the contents of this string for any use.
 
 struc FAT32_ebpb_t
-    .u32_FATSz             resb 4      ; size of *each* fat in sectors, total = FATSz * (# of FATs)
+    .u32_FATSz             resd 1      ; size of *each* fat in sectors, total = FATSz * (# of FATs)
-    .u16_ExtFlags          resb 2
+    .u16_ExtFlags          resw 1
-    .u16_FSVersion         resb 2
+    .u16_FSVersion         resw 1
-    .u32_RootDirCluster    resb 4
+    .u32_RootDirCluster    resd 1
-    .u16_FSInfoSector      resb 2
+    .u16_FSInfoSector      resw 1
-    .u16_BkBootSector      resb 2
+    .u16_BkBootSector      resw 1
-    .reserved1             resb 12
+    .reserved0             resb 12
     .u8_DriveNumber        resb 1
     .u8_NtFlags            resb 1
     .u8_Signature          resb 1
-    .u32_VolumeId          resb 4
+    .u32_VolumeId          resd 1
     .volume_label          resb 11
     .system_ident          resb 8      ; Should always be 'FAT32   '
 endstruc

src/stage2/stage2.nasm

@@ -258,7 +258,7 @@ ReadVbrData:
     cmp word [bx + 0x1FE], 0xAA55           ; check for bytes at end
     jne ReadVbrData.error_nosign
 .check_FAT_size:
-    test word [bx + FAT32_bpb_t.unused2_ZERO_word], 0      ; TotSectors16 will not be set if FAT32
+    test word [bx + FAT32_bpb_t.u16_TotalSectors16], 0      ; TotSectors16 will not be set if FAT32
     jnz ReadVbrData.error_badfatfs
 .endp:
     __CDECL16_PROC_EXIT

src/vbr/vbr.nasm

@@ -21,15 +21,21 @@
 %define __STEVIA_VBR
 section .text
 __ENTRY:
-phy_bpb_start:
+    ; try to force encode a short jmp nop: i.e 0xEB 0x5A 0x90
+    ; will jump right 0x5A (90 bytes) after the end of the ebpb
+    ; this could also be encoded as 0xE9 0x?? 0x?? for a near jump
+    ; if init ends up being >= 128 bytes from entry.
     jmp short (init - $$)
     nop
 
-; fill BPB area with 0x00 since we skip writing this part to disk
+; 8 ascii bytes, "MSWIN 4.1", ""
-; but we need it for the 'jmp short entry; nop' above
+phy_bs_ident:
-times 33 db 0x00
+times 8 db 0x00
+
+phy_bpb_start:
+times 25 db 0x00
+
 phy_ebpb_start:
-; fill eBPB area with 0x00 since we skip writing this part to disk
 times 54 db 0x00
 
 ; ###############
@@ -95,7 +101,7 @@ main:
     mov byte [bp - 2], dl                                  ; boot_drive
 .check_FAT_size:                                           ; we only support a very specific setup of FAT32
     mov bx, phy_bpb_start
-    test word [bx + FAT32_bpb_t.unused2_ZERO_word], 0      ; TotSectors16 will not be set if FAT32
+    test word [bx + FAT32_bpb_t.u16_TotalSectors16], 0      ; TotSectors16 will not be set if FAT32
     jz main.load_stage2
     ERROR VBR_ERROR_WRONG_FAT_SIZE
 .load_stage2: