Add boot capability in MBR

partition() is now able to create an active and bootable primary MBR partition with  universal boot code (LBA/CHS).

Author: maxpat78

FATtools/partutils.py

@@ -148,6 +148,9 @@ class MBR(object):
     0x1FE: ('wBootSignature', '<H') # 55 AA
     } # Size = 0x200 (512 byte)
 
+    # my universal boot code
+    boot_code =  b'\x31\xC9\xFA\x8E\xD1\xBC\x00\x7C\x8E\xD9\x8E\xC1\xFB\x89\xE3\x89\xDE\xBF\x00\x06\xB9\x00\x01\xFC\xF3\xA5\xEA\x1F\x06\x00\x00\xBE\xBE\x07\x80\x3C\x80\x74\x1C\x83\xC6\x10\x81\xFE\xFE\x07\x7C\xF2\xBE\x86\x06\xAC\x3C\x00\x74\x08\x31\xDB\xB4\x0E\xCD\x10\xEB\xF3\xF4\xEB\xFD\xB4\x42\x87\xFE\xBE\x5C\x06\x8B\x4D\x08\x89\x4C\x08\x8B\x4D\x0A\x89\x4C\x0C\xCD\x13\x87\xFE\x73\x1D\x10\x00\x01\x00\x00\x7C\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xB8\x01\x02\x8B\x4C\x02\x8A\x74\x01\xCD\x13\x72\xB7\x81\x3E\xFE\x07\x55\xAA\x75\xAF\xEA\x00\x7C\x00\x00\x4E\x6F\x74\x68\x69\x6E\x67\x20\x74\x6F\x20\x62\x6F\x6F\x74\x2E\x00'
+
     def __init__ (self, s=None, offset=0, stream=None, disksize=0, sector=512):
         self._sector = sector # physical sector size (512 or 4096)
         self._i = 0
@@ -157,6 +160,7 @@ def __init__ (self, s=None, offset=0, stream=None, disksize=0, sector=512):
         self.heads_per_cyl = 0 # Heads Per Cylinder (max 255)
         self.sectors_per_cyl = 0 # Sectors Per Cylinder (max 63)
         self.is_lba = 0
+        self.is_bootable = False # determine if add boot code and set bStatus
         self._kv = self.layout.copy()
         self._vk = {} # { name: offset}
         self.partitions = []
@@ -175,6 +179,8 @@ def __init__ (self, s=None, offset=0, stream=None, disksize=0, sector=512):
     def pack(self, sector=512):
         "Update internal buffer"
         self.wBootSignature = 0xAA55 # set valid record signature
+        if self.is_bootable:
+            self._buf[0:len(self.boot_code)] = self.boot_code
         for k, v in list(self._kv.items()):
             self._buf[k:k+struct.calcsize(v[1])] = struct.pack(v[1], getattr(self, v[0]))
         for i in self.partitions:
@@ -214,7 +220,6 @@ def setpart(self, index, start, size):
             pa.sLastSectorCHS = chs2raw((1023, 254, 63))
         else:
             pa.sLastSectorCHS = chs2raw(pa.sLastSectorCHS)
-        #~ if index==0: pa.bStatus = 0x80 # always set as active
         pa.bType = get_min_mbrtype(size) # effective type must be set after formatting
         if index > 0:
             pa.bType = 5 # Extended CHS
@@ -257,13 +262,14 @@ def mkpart(self, offset, size):
         return dwFirstSectorLBA, dwTotalSectors, sFirstSectorCHS, sLastSectorCHS
 
 def partition(disk, fmt='gpt', options={}):
-    "Makes a single partition with all disk space"
+    "Makes a single partition with all disk space (and makes it bootable if MBR)"
     disk.seek(0)
     SECTOR = options.get('phys_sector', 512)
     if fmt == 'mbr':
         part_size = disk.size
         if options.get('compatibility',1) == 0 and part_size > (2<<30): part_size = (2<<30)
         mbr = MBR(None, disksize=disk.size, sector=SECTOR)
+        mbr.is_bootable = True
         if disk.type() == 'VHD':
             c, mbr.heads_per_cyl, mbr.sectors_per_cyl = struct.unpack('>HBB',disk.footer.dwDiskGeometry)
         elif disk.type() == 'VDI':
@@ -282,6 +288,7 @@ def partition(disk, fmt='gpt', options={}):
         else:
             options['mbr_type'] = mbr.partitions[0].bType
         if DEBUG&1: log("Made a MBR primary partition, type %X: %s", options['mbr_type'], mbr_types[options['mbr_type']])
+        mbr.partitions[0].bStatus = 0x80 # mark as active (required by DOS)
         # Remove any previous GPT structure
         disk.write(32768*b'\x00')
         disk.seek(0)

FATtools/version.py

@@ -1 +1 @@
-__version__ = '1.0.35'
+__version__ = '1.0.36'

nodos/MYMBR

@@ -0,0 +1,102 @@
+; A generic Master Boot Record for IBM PC compatible
+; x86 16-bit boot code
+;
+; Works both with LBA and CHS partitions marked as bootable.
+;
+; compile with nasm mymbr.asm
+
+; BIOS loads it at 7C00h, we relocate it to traditional address
+org 600h
+
+    ; set DS=SS=ES=0 and SP=code origin
+    xor cx, cx
+    cli
+    mov ss, cx
+    mov sp, 7C00h
+    mov ds, cx
+    mov es, cx
+    sti
+
+    mov bx, sp
+    ; relocate 512 bytes (100h words) to 600h
+    mov si, bx
+    mov di, 600h
+    mov cx, 100h
+    cld
+    repe movsw
+    ; shorter?
+    ;push cx
+    ;push 0x61F
+    ;retf
+    jmp 0x0000:0x61F ; jump to (relocated) next instruction
+
+    mov si, 7BEh ; partition table start at +1BEh (byte 80h/00h for bootable/not bootable)
+IsBootablePart:
+    cmp byte [si], 80h
+    jz LoadInt13_42H
+    add si, 10h ; part. entry size
+    cmp si, 7FEh
+    jl IsBootablePart
+
+PrintMsg:
+    mov si, NoBoot
+PrintLoop:
+    lodsb
+    cmp al, 0
+    jz Exit
+    xor bx, bx
+    mov ah, 0Eh ; output char in AL with attribute in BX
+    int 10h
+    jmp PrintLoop
+Exit:
+    ;int 18h ; diskless boot hook
+    hlt
+    jmp Exit
+
+LoadInt13_42H:
+    mov ah, 42h ; extended read in LBA mode from drive DL (preset by BIOS)
+    xchg di, si
+    mov si, dap ; disk address packet
+    mov cx, [di+8] ; put LBA sector to read (LO-HI bytes) into dap
+    mov [si + DAP.LBAlo], cx
+    mov cx, [di+10]
+    mov [si + DAP.LBAhi], cx
+    ; stc
+    int 13h
+    xchg di, si ; partition pointer back to SI
+    jnc CheckMagic ; else, try with CHS read
+
+struc DAP
+  .size    : resb 1
+  .unused  : resb 1
+  .sectors : resw 1
+  .buffer   : resd 1
+  .LBAlo   : resd 1
+  .LBAhi   : resd 1
+endstruc
+
+dap:
+    istruc DAP
+    at DAP.size,    db 16
+    at DAP.unused,  db 0
+    at DAP.sectors, dw 1                 ; how many
+    at DAP.buffer,   dd 00007C00h         ; buffer address (0000:7C00h)
+    at DAP.LBAlo,   dd 0                 ; which sector?
+    at DAP.LBAhi,   dd 0
+    iend
+
+LoadInt13_02H:
+    mov ax, 0201h ; read 1 sector from drive DL, C-H-S in CH-DH-CL, to ES:BX
+    ;mov bx, 7C00h ; pre-loaded above
+    mov cx, [si+2] ; C-H-S in partition entry
+    mov dh, [si+1]
+    ; stc
+    int 13h
+    jc PrintMsg
+CheckMagic:
+    cmp word [7FEh], 0xAA55 ; magic in last sector word?
+    jnz PrintMsg
+    jmp 0x0000:0x7C00 ; jump to Boot Sector code, with DL=boot drive and DS:SI=partition booted
+
+NoBoot:
+db "Nothing to boot.", 0

nodos/MYMBR.ASM

@@ -0,0 +1 @@
+print ("Stringifying MBR code...\n", ''.join(['\\x%02X' % c for c in open('mymbr','rb').read()]))