minor changes in fat32

put in $(qtpaths --paths GenericDataLocation)

.gitignore

@@ -11,3 +11,4 @@ stevia-log
 compose-dev.yaml
 eth_null-tx.log
 eth_null-txdump.txt
+*.log

Makefile

@@ -38,9 +38,6 @@ QEMU_ARGS := \
     -device e1000,netdev=n0,mac=52:54:00:12:34:56 \
     -netdev user,id=n0 \
     -device piix3-usb-uhci \
-    -device usb-ohci,id=ohci0 \
-    -device usb-ehci,id=ehci0 \
-    -device pcspk \
     -parallel null \
     -serial null -serial none -serial none -serial none \
     -chardev file,id=dbg,path=bochs-e9.log,append=on \

docs/okteta/structures/mbr/main.osd

@@ -0,0 +1,24 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<data>
+  <struct name="MBR">
+    <!-- 446 bytes: bootstrap code -->
+    <array name="bootCode" length="446">
+      <primitive type="UInt8"/>
+    </array>
+
+    <!-- 4 x 16-byte partition entries -->
+    <array name="partitions" length="4">
+      <struct name="PartitionEntry">
+        <primitive name="status" type="UInt8"/>         <!-- 0x80=bootable -->
+        <array name="chsFirst" length="3"><primitive type="UInt8"/></array>
+        <primitive name="type" type="UInt8"/>
+        <array name="chsLast" length="3"><primitive type="UInt8"/></array>
+        <primitive name="lbaStart" type="UInt32"/>
+        <primitive name="lbaSectors" type="UInt32"/>
+      </struct>
+    </array>
+
+    <!-- Signature 0x55AA (little-endian UInt16 == 0xAA55 on disk) -->
+    <primitive name="signature" type="UInt16"/>
+  </struct>
+</data>

docs/okteta/structures/mbr/metadata.desktop

@@ -0,0 +1,12 @@
+[Desktop Entry]
+Icon=application-x-executable
+Type=Service
+ServiceTypes=KPluginInfo
+Name=Stevia MBR Structure
+X-KDE-PluginInfo-Author=Elaina Claus
+X-KDE-PluginInfo-Name=mbr
+X-KDE-PluginInfo-Version=1.0
+X-KDE-PluginInfo-Website=https://chtm.me
+X-KDE-PluginInfo-Category=structure
+X-KDE-PluginInfo-License=MIT
+X-KDE-PluginInfo-EnabledByDefault=false

docs/okteta/structures/vbr/main.osd

@@ -0,0 +1,57 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<data>
+  <struct name="VBR">
+    <!-- 3 bytes: jmp over bpb code -->
+    <array name="jmpcode" length="3">
+      <primitive name="opcode" type="UInt8"/>
+    </array>
+
+    <array name="bs_ident" length="8">
+      <primitive type="Char"/>
+    </array>
+
+    <struct name="FAT32_bpb">
+      <primitive name="BytesPerSector" type="UInt16"/>
+      <primitive name="SectorsPerCluster" type="UInt8"/>
+      <primitive name="ReservedSectors" type="UInt16"/>
+      <primitive name="FatCount" type="UInt8"/>
+      <primitive name="RootEntryCount16" type="UInt16"/>
+      <primitive name="TotalSectors16" type="UInt16"/>
+      <primitive name="MediaDesc" type="UInt8"/>
+      <primitive name="FATSize16" type="UInt16"/>
+      <primitive name="SectorsPerTrack" type="UInt16"/>
+      <primitive name="HeadCount" type="UInt16"/>
+      <primitive name="HiddenSectors" type="UInt32"/>
+      <primitive name="TotalSectors32" type="UInt32"/>
+    </struct>
+
+    <struct name="FAT32_ebpb">
+      <primitive name="FATSize32" type="UInt32"/>
+      <primitive name="ExtFlags" type="UInt16"/>
+      <primitive name="FSVersion" type="UInt16"/>
+      <primitive name="RootDirCluster" type="UInt32"/>
+      <primitive name="FSInfoSector" type="UInt16"/>
+      <primitive name="BkBootSector" type="UInt16"/>
+      <array name="reserved0" length="12">
+        <primitive type="uint8"/>
+      </array>
+      <primitive name="DriveNumber" type="UInt8"/>
+      <primitive name="NtFlags" type="UInt8"/>
+      <primitive name="Signature" type="UInt8"/>
+      <primitive name="VolumeId" type="UInt32"/>
+      <array name="VolumeLabel" length="11">
+        <primitive type="Char"/>
+      </array>
+      <array name="FilesystemIdent" length="8">
+        <primitive type="Char"/>
+      </array>
+    </struct>
+
+    <array name="BootCode" length="420">
+      <primitive type="UInt8"/>
+    </array>
+
+    <!-- Signature 0xAA55 -->
+    <primitive name="signature" type="UInt16"/>
+  </struct>
+</data>

docs/okteta/structures/vbr/metadata.desktop

@@ -0,0 +1,12 @@
+[Desktop Entry]
+Icon=application-x-executable
+Type=Service
+ServiceTypes=KPluginInfo
+Name=Stevia FAT32 VBR Structure
+X-KDE-PluginInfo-Author=Elaina Claus
+X-KDE-PluginInfo-Name=vbr32
+X-KDE-PluginInfo-Version=1.0
+X-KDE-PluginInfo-Website=https://chtm.me
+X-KDE-PluginInfo-Category=structure
+X-KDE-PluginInfo-License=MIT
+X-KDE-PluginInfo-EnabledByDefault=false

include/BIOS/func/ext_read.nasm

@@ -51,7 +51,7 @@ endstruc
 ;                         uint32_t lba,
 ;                         uint16_t count, uint8_t drive_num)
 ALIGN 4, db 0x90
-read_disk_raw:
+BIOS_int13h_ext_read:
     __CDECL16_PROC_ENTRY
 .func:                         
     push LBAPkt_t_size        ; len

include/error_codes.inc

@@ -15,8 +15,7 @@
 
 %ifndef __INC_ERROR_CODES
 
-; Errors
+; MBR Error codes
-; 12 Errors, 5 in use
 %define MBR_ERROR_DISK_T_ERR         'a'
 %define MBR_ERROR_NO_INT32E          'b'
 %define MBR_ERROR_NO_NO_BOOT_PART    'c'
@@ -30,7 +29,7 @@
 %define MBR_ERROR_RESERVED_k         'k'
 %define MBR_ERROR_INT13h_EREAD_ERR   'l'
 
-; 12 Error
+; VBR Error codes
 %define VBR_ERROR_WRONG_FAT_SIZE     'm'
 %define VBR_ERROR_NO_SIGNATURE       'n'
 %define VBR_ERROR_DISK_READ_ERR      'o'
@@ -44,7 +43,7 @@
 %define VBR_ERROR_RESERVED_w         'w'
 %define VBR_ERROR_RESERVED_x         'x'
 
-; 22 errors, 8 in use
+; Stage2 Error codes
 %define STAGE2_A20_FAILED            'A'
 %define STAGE2_SIGNATURE_MISSING     'B'
 %define STAGE2_MM_E820_NO_SUPPORT    'C'
@@ -60,19 +59,19 @@
 %define STAGE2_FAT32_E_UNSUPPORTED   'M'
 %define STAGE2_FAT32_E_UNIMPLEMENTED 'N'
 %define STAGE2_ERROR_BAD_MBR         'O'
-%define STAGE2_ERROR_BAD_VBR         'P'
+%define STAGE2_VBR_E_ACTIVE          'P'
-%define STAGE2_ERROR_RESERVED_Q      'Q'
+%define STAGE2_VBR_E_SIGN            'Q'
-%define STAGE2_ERROR_RESERVED_R      'R'
+%define STAGE2_VBR_E_TOT             'R'
-%define STAGE2_ERROR_RESERVED_S      'S'
+%define STAGE2_VBR_E_FATSZ           'S'
-%define STAGE2_ERROR_RESERVED_T      'T'
+%define STAGE2_VBR_E_DIRENT          'T'
-%define STAGE2_ERROR_RESERVED_U      'U'
+%define STAGE2_VBR_E_PARTTYPE        'U'
-%define STAGE2_ERROR_RESERVED_V      'V'
+%define STAGE2_RESERVED_E_V          'V'
 
-; for development only, specific errors should be above.
+; Debug error codes
-%define STEVIA_DEBUG_OK      'W'
+%define STEVIA_DEBUG_OK              'W'
-%define STEVIA_DEBUG_ERR      'X'
+%define STEVIA_DEBUG_ERR             'X'
-%define STEVIA_DEBUG_UNIMPLEMENTED      'Y'
+%define STEVIA_DEBUG_UNIMPLEMENTED   'Y'
-%define STEVIA_DEBUG_HALT      'Z'
+%define STEVIA_DEBUG_HALT            'Z'
 
 %endif
 %define __INC_ERROR_CODES

include/fat32/FAT32_SYS.nasm

@@ -16,9 +16,169 @@
 %ifndef __INC_FAT32_SYS
 
 %include "partition_table.inc"
-%include "fat32/bpb_offset_bx.inc"
 %include "fat32/fat32_structures.inc"
 
+; int read_mbr(int boot_drive, void* dst)
+; destination buffer needs 512 bytes of space
+FAT32_load_mbr:
+    __CDECL16_PROC_ENTRY
+.proc:
+    ; read mbr on boot drive to memory (for the partition table)
+    movzx ax, byte [bp + 4]
+    push ax                                 ; drive_num (2)
+    push 0x01                               ; count (2)
+
+    push dword 0x0                          ; lba (4)
+
+    push word [bp + 6]                      ; offset = dst
+    push __STAGE2_SEGMENT                   ; this segment 
+    call BIOS_int13h_ext_read
+    add sp, 0xC
+.check_sig:
+    mov bx, [bp + 6]
+    cmp word [bx + 0x1FE], 0xAA55           ; check for bytes at end
+    jne .error_nosign
+    ; TODO: this needs more error checking, zero checking, check the sig a bunch of stuff...
+.endp:
+    __CDECL16_PROC_EXIT
+    ret
+.error_nosign:
+    ERROR STAGE2_ERROR_BAD_MBR
+
+; int read_vbr(int boot_drive, void* buf)
+; read vbr on boot partition to memory (for fat bpb/ebpb)
+; TODO: seperate validation and loading the sector, just check the 0xAA55 at the end here...
+FAT32_load_vbr:
+    __CDECL16_PROC_ENTRY
+.proc:
+    mov bx, SteviaInfo
+    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
+
+.find_active_L0:
+    mov al, [bx + PartEntry_t.attributes]
+    cmp al, 0x80                            ; 0x80 == 1000_0000b
+    je .check_fstype
+    add bx, PartEntry_t_size                ; next part entry's attributes
+    loop .find_active_L0
+    jmp .error_noactive
+.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 .active_ok
+    ; *or*
+    cmp al, 0x1C
+    je .active_ok
+
+    jmp .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)
+
+    mov eax, dword [bx + PartEntry_t.lba_start]
+    push dword eax                          ; lba (4)
+
+    push word [bp + 6]                      ; offset = dst
+    push __STAGE2_SEGMENT                   ; this segment 
+    call BIOS_int13h_ext_read
+    add sp, 0xC
+    ; vbr (with fat bpb/ebpb) is at the buffer now
+.check_sig:
+    mov bx, [bp + 6]
+    cmp word [bx + 0x1FE], 0xAA55           ; check for bytes at end
+    jne .error_nosign
+.check_FAT_sanity:
+    ; we only quickly validate that this is *probably* a FAT32 volume
+
+    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 .error_totsectors
+
+    cmp word [bx + FAT32_bpb_t.u16_FATSize16], 0           ; FatSize16 will be 0 if FAT32 (use FATSize32 in ebpb)
+    jne .error_fatsz
+
+    cmp word [bx + FAT32_bpb_t.u16_RootEntryCount16], 0    ; root dir info is in data clusters on fat32
+    jne .error_rootdir
+.endp:
+    __CDECL16_PROC_EXIT
+    ret
+.error_noactive:
+    ERROR STAGE2_VBR_E_ACTIVE
+.error_nosign:
+    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
+
+; what a 'mount' should probably do at this point...
+; - read VBR at partition_lba
+; - validate FAT32 signatures
+; - fill fat32_bpb_t and compute derived fields
+; - read FSInfo (free count/next free)
+; - ???
+; int fat32_mount(FAT32_State_t* state, uint32_t partition_lba);
+FAT32_mountfs:
+    __CDECL16_PROC_ENTRY
+.proc:
+    ; mount: parse BPB, derive fat0_lba, data_lba, cluster0_lba.
+
+.endp:
+    __CDECL16_PROC_EXIT
+    ret
+.error:
+    ERROR STEVIA_DEBUG_ERR
+
+
+; int fat32_read_fat(FAT32_State_t* state, uint32_t clus, uint32_t* out);
+FAT32_read_fat:
+    __CDECL16_PROC_ENTRY
+.proc:
+    ; Read 32-bit FAT entry for cluster n
+.endp:
+    __CDECL16_PROC_EXIT
+    ret
+.error:
+    ERROR STEVIA_DEBUG_ERR
+
+; FAT32 entry is 32-bits; only low 28 bits are meaningful.
+;   EOC if (val & 0x0FFFFFFF) >= 0x0FFFFFF8.
+;   bad if == 0x0FFFFFF7.
+;   free if == 0x00000000.
+; int fat32_next_clus(FAT32_State_t* state, uint32_t clus, uint32_t* out_next);
+FAT32_next_cluster:
+    __CDECL16_PROC_ENTRY
+.proc:
+    ; Walk to next cluster in chain (validates EOC/bad)
+.endp:
+    __CDECL16_PROC_EXIT
+    ret
+.error:
+    ERROR STEVIA_DEBUG_ERR
+
+; e.g:
+; uint64_t clus_to_lba(FAT32_State_t* state, uint32_t clus) {
+;  return v->data_lba + (uint64_t)(clus - 2) * v->secs_per_clus;
+; }
+FAT32_clus_to_lba:
+    __CDECL16_PROC_ENTRY
+.proc:
+    ; Convert cluster -> LBA of first sector of that cluster
+.endp:
+    __CDECL16_PROC_EXIT
+    ret
+.error:
+    ERROR STEVIA_DEBUG_ERR
+
 ; Prototyping for now...
 
 ; TODO:
@@ -59,35 +219,6 @@
 ; int cache_read_sector(uint64_t lba, void* dst);   
 ; int cache_invalidate_all(void);
 
-; what a 'mount' should probably do at this point...
-; - read VBR at partition_lba
-; - validate FAT32 signatures
-; - fill fat32_bpb_t and compute derived fields
-; - read FSInfo (free count/next free)
-; - ???
-; int fat32_mount(uint32_t partition_lba, fat32_bpb_t* out);
-
-
-;
-; Accessors
-;
-
-; // Convert cluster -> LBA of first sector of that cluster
-; uint64_t clus_to_lba(const fat32_bpb_t* v, uint32_t clus) {
-;  return v->data_lba + (uint64_t)(clus - 2) * v->secs_per_clus;
-; }
-
-; FAT32 entry is 32-bits; only low 28 bits are meaningful.
-;   EOC if (val & 0x0FFFFFFF) >= 0x0FFFFFF8.
-;   bad if == 0x0FFFFFF7.
-;   free if == 0x00000000.
-
-; // Read 32-bit FAT entry for cluster n
-; int fat32_read_fat(const fat32_bpb_t* v, uint32_t clus, uint32_t* out);
-
-; // Walk to next cluster in chain (validates EOC/bad)
-; int fat32_next_clus(const fat32_bpb_t* v, uint32_t clus, uint32_t* out_next);
-
 ;
 ; SFN directories
 ;
@@ -109,7 +240,6 @@
 ;int fat32_dir_iter_open(fat32_bpb_t* v, uint32_t first_clus, fat32_dir_iter_t* it);
 ;int fat32_dir_iter_next(fat32_dir_iter_t* it, fat32_dirent_sfn_t* out); // FS_OK or FS_E_END
 
-
 ; typedef struct {
 ;   uint32_t first_clus;
 ;   uint32_t size;

include/fat32/fat32_structures.inc

@@ -58,20 +58,18 @@
 ;                           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
-    .bytes_per_sector_word          resb 2
+    .u16_ReservedSectors     resw 1
-    .sectors_per_cluster_byte       resb 1
+    .u8_FatCount             resb 1
-    .reserved_sectors_word          resb 2
+    .u16_RootEntryCount16    resw 1      ; Root dir entry count field, 0 on fat32
-    .fat_count_byte                 resb 1
+    .u16_TotalSectors16      resw 1      ; total number of sectors size, 0 on fat32
-    .unused1_ZERO_word              resb 2      ; Root entry count field, 0 on fat32
+    .u8_MediaDesc            resb 1
-    .unused2_ZERO_word              resb 2      ; total sectors size 16, 0 on fat32
+    .u16_FATSize16           resw 1      ; FAT size 16, 0 on fat32
-    .media_desc_byte                resb 1
+    .u16_SectorsPerTrack     resw 1
-    .unused3_ZERO_word              resb 2      ; FAT size 16, 0 on fat32
+    .u16_HeadCount           resw 1
-    .sectors_per_track_word         resb 2
+    .u32_HiddenSectors       resd 1
-    .head_count_word                resb 2
+    .u32_TotalSectors32      resd 1
-    .hidden_sectors_dword           resb 4
-    .total_sectors_dword            resb 4
 endstruc
 
 ; EBPB Information (FAT32)
@@ -91,19 +89,19 @@ 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
-    .FATSz_dword                resb 4
+    .u32_FATSize32         resd 1      ; size of *each* fat in sectors, total = FATSz * (# of FATs)
-    .extflags_word              resb 2
+    .u16_ExtFlags          resw 1
-    .FSVersion_word             resb 2
+    .u16_FSVersion         resw 1
-    .root_clus_dword            resb 4
+    .u32_RootDirCluster    resd 1
-    .FSInfo_word                resb 2
+    .u16_FSInfoSector      resw 1
-    .BkBootSec_word             resb 2
+    .u16_BkBootSector      resw 1
-    .reserved1                  resb 12
+    .reserved0             resb 12
-    .drive_number_byte          resb 1
+    .u8_DriveNumber        resb 1
-    .nt_flags_byte              resb 1
+    .u8_NtFlags            resb 1
-    .signature_byte             resb 1
+    .u8_Signature          resb 1
-    .volume_id_dword            resb 4
+    .u32_VolumeId          resd 1
-    .volume_label_bytea         resb 11
+    .volume_label          resb 11
-    .system_ident_bytea         resb 8
+    .system_ident          resb 8      ; Should always be 'FAT32   '
 endstruc
 
 ; ## Standard 8.3 structure ###
@@ -197,20 +195,11 @@ endstruc
 
 ; 32 bytes
 struc FAT32_State_t
-    .first_data_sector_32     resd 1
+    .u32_TotalClusters        resd 1
-    .first_fat_sector_32      resd 1
+    .u32_DataAreaStartSector  resd 1
-    .fat_size_32              resd 1
+    .u32_FATAreaStartSector   resd 1
-    .curr_FAT_cluster_32      resd 1
+    .p16_FATBuffer            resw 1
-    .curr_dir_cluster_32      resd 1
+    .p16_ClustBuffer          resw 1
-    .curr_drive_lba_32        resd 1
-endstruc
-
-; 16 bytes
-struc FAT32_NextClusterData_t
-    .fat_offset               resd 1
-    .fat_sector               resd 1
-    .entry_offset             resd 1
-    .reserved_1               resd 1
 endstruc
 
 ; FAT32 Attributes

src/mbr/mbr.nasm

@@ -133,7 +133,7 @@ main:
         ; uint8_t read_stage2_raw(uint16_t buf_segment, uint16_t buf_offset, 
         ;                         uint32_t lba,
         ;                         uint16_t count, uint16_t drive_num)
-        call read_disk_raw
+        call BIOS_int13h_ext_read
         add sp, 0xC
     .goto_vbr:
         cmp word [VBR_ENTRY + 0x1FE], 0xAA55

src/stage2/stage2.nasm

@@ -91,7 +91,7 @@ init:
 
 %include "partition_table.inc"
 %include "fat32/fat32_structures.inc"
-;%include 'fat32/FAT32_SYS.inc'
+%include 'fat32/FAT32_SYS.nasm'
 
 ; ###############
 ; BIOS functions
@@ -135,7 +135,7 @@ main:
     push ax                                         ; dst
     movzx ax, byte [u8_BootDrive]                     
     push ax                                         ; boot_drive
-    __CDECL16_CALL ReadMbrData, 2                   ; fill mbr buffer
+    __CDECL16_CALL FAT32_load_mbr, 2                ; fill/validate mbr buffer
 
     ; setup heap space for vbr data
     __CDECL16_CALL_ARGS 0x200, 0x10
@@ -145,7 +145,7 @@ main:
     push ax                                         ; dst
     movzx ax, byte [u8_BootDrive]
     push ax                                         ; boot_drive
-    __CDECL16_CALL ReadVbrData, 2                   ; fill vbr buffer
+    __CDECL16_CALL FAT32_load_vbr, 2                ; fill/validate vbr buffer
 
     ; enable A20 gate
     call EnableA20
@@ -194,82 +194,6 @@ hcf:
 ;
 ; ##############################
 
-; int read_mbr(int boot_drive, void* dst)
-; destination buffer needs 512 bytes of space
-ReadMbrData:
-    __CDECL16_PROC_ENTRY
-.proc:
-    ; read mbr on boot drive to memory (for the partition table)
-    movzx ax, byte [bp + 4]
-    push ax                                 ; drive_num (2)
-    push 0x01                               ; count (2)
-
-    push dword 0x0                          ; lba (4)
-
-    push word [bp + 6]                      ; offset = dst
-    push __STAGE2_SEGMENT                   ; this segment 
-    call read_disk_raw
-    add sp, 0xC
-.check_sig:
-    mov bx, [bp + 6]
-    cmp word [bx + 0x1FE], 0xAA55           ; check for bytes at end
-    jne ReadMbrData.error_nosign
-    ; TODO: this needs more error checking, zero checking, check the sig a bunch of stuff...
-.endp:
-    __CDECL16_PROC_EXIT
-    ret
-.error_nosign:
-    ERROR STAGE2_ERROR_BAD_MBR
-
-; int read_vbr(int boot_drive, void* buf)
-; read vbr on boot partition to memory (for fat bpb/ebpb)
-ReadVbrData:
-    __CDECL16_PROC_ENTRY
-.proc:
-    mov bx, SteviaInfo
-    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
-    add bx, PartEntry_t_size                ; next part entry's attributes
-    loop ReadVbrData.find_active_L0
-    jmp ReadVbrData.error_noactive
-.active_found:
-    movzx ax, byte [bp + 4]
-    push ax                                 ; drive_num (2)
-    push 0x01                               ; count (2)
-
-    mov eax, dword [bx + PartEntry_t.lba_start]
-    push dword eax                          ; lba (4)
-
-    push word [bp + 6]                      ; offset = dst
-    push __STAGE2_SEGMENT                   ; this segment 
-    call read_disk_raw
-    add sp, 0xC
-    ; vbr (with fat bpb/ebpb) is at the buffer now
-.check_sig:
-    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.unused2_ZERO_word], 0      ; TotSectors16 will not be set if FAT32
-    jnz ReadVbrData.error_badfatfs
-.endp:
-    __CDECL16_PROC_EXIT
-    ret
-.error_noactive:
-    ERROR STAGE2_ERROR_BAD_VBR
-.error_nosign:
-    ERROR STAGE2_ERROR_BAD_VBR
-.error_badfatfs:
-    ERROR STAGE2_ERROR_BAD_VBR
-
 ; set ds and es segments back to the base of the loader
 %ifnmacro __TINY_DS_ES
 %macro __TINY_DS_ES 0
@@ -529,17 +453,19 @@ align 16, resb 1
 %define BIOSMemoryMap_SIZE 1024
 BIOSMemoryMap:
     resb BIOSMemoryMap_SIZE
-
-align 16, resb 1
-stack_bottom:
-    resb 2048
-stack_top:
 end_bss:
+; !!! End bss data !!!
+%define STACK_SIZE 0x1000       ; 4 KiB
 
 ; Pad to the cap (emits nothing in the file; only increases .bss virtual size).
 ; If BSS_SIZE > BSS_MAX_BYTES, this becomes negative and NASM errors out.
-%define BSS_MAX_BYTES 0x2000
+%define BSS_MAX_BYTES (0x2000 - STACK_SIZE)
 resb (BSS_MAX_BYTES - (end_bss - begin_bss))
 
+align 16, resb 1
+stack_bottom:
+    resb STACK_SIZE
+stack_top:
+
 ; Optional: keep a label for later math:
 bss_cap_end:

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:
@@ -114,7 +120,7 @@ main:
     ; uint8_t read_stage2_raw(uint16_t buf_segment, uint16_t buf_offset, 
     ;                         uint32_t lba,
     ;                         uint16_t count, uint16_t drive_num)
-    call read_disk_raw
+    call BIOS_int13h_ext_read
     add sp, 0xC
 .enter_stage2:
     mov dl, byte [bp - 2]                ; byte boot_drive