我正在关注breakthorn OS开发系列，直到现在我能够成功运行bootloader stage1，但是在linux机器（ubuntu 16.04）上的bochs模拟器中从FAT12软盘加载第二阶段引导加载程序存在一些问题（它在虚拟机中运行良好）。这是我的 stage1 引导加载程序：
bits 16
org 0 ;we will set segments later
start: jmp main
;***** BPB Parameter block *****
;must start 3 bytes after start (jmp main is of 3 byte)
bpbOEM db "My OS " ; OEM identifier (Cannot exceed 8 bytes!)
bpbBytesPerSector: DW 512
bpbSectorsPerCluster: DB 1
bpbReservedSectors: DW 1
bpbNumberOfFATs: DB 2
bpbRootEntries: DW 224
bpbTotalSectors: DW 2880
bpbMedia: DB 0xf8 ;; 0xF1
bpbSectorsPerFAT: DW 9
bpbSectorsPerTrack: DW 18
bpbHeadsPerCylinder: DW 2
bpbHiddenSectors: DD 0
bpbTotalSectorsBig: DD 0
bsDriveNumber: DB 0
bsUnused: DB 0
bsExtBootSignature: DB 0x29
bsSerialNumber: DD 0xa0a1a2a3
bsVolumeLabel: DB "MOS FLOPPY "
bsFileSystem: DB "FAT12 "
Print:
;string pointed by ds:si, terminated by 0
lodsb ;load next byte pointed by si to al
or al, al ;if al is zero
jz PrintDone
mov ah, 0eh ;prepare fro bios vedio interuppt call
int 10h
jmp Print
PrintDone:
ret
ReadSectors :
;cx = no fo sectors to ReadSectors
;ax = strating sectors
;ES:BX = buffer to read to
.MAIN :
mov di, 0x0005 ;we will try 5 times if failed
.SECTORLOOP :
push ax
push bx
push cx
call LBACHS ;we will get absolute sector, absolute head and absolute track information from here
mov ah, 0x02 ;prepare bios read interrupt
mov al, 0x01 ;we will read one sector
mov ch, byte[absoluteTrack]
mov cl, byte[absoluteSector]
mov dh, byte[absoluteHead]
mov dl, byte[bsDriveNumber]
int 0x13 ;bios read interrupt call
jnc .SUCCESS ;if sucessful
xor ax, ax ;retying again
int 0x13 ;reset disk interuppt call
dec di ;decrease a try
pop cx
pop bx
pop ax
jnz .SECTORLOOP
int 0x18 ;start basic
.SUCCESS:
pop cx
pop bx
pop ax
add bx, word[bpbBytesPerSector] ;next read buffer location
inc ax ;next sector to read
loop .MAIN
ret
ClusterLBA:
;convert custer no to LBACHS
;LBA = (cluster - 2)*sectors per cluster
sub ax, 0x0002
xor cx, cx
mov cl, byte[bpbSectorsPerCluster]
mul cx
add ax, word[datasector] ;base of data sectors
ret
LBACHS:
;convert LBA to CHS
;absolute sector = (logical sector % sector per track) + 1
;absolute head = (logical sector / sectors per track) % no of heads
;absoluteTrack = logical sector / (sectors per track * no of heads)
xor dx, dx
div word [bpbSectorsPerTrack]
inc dl
mov byte[absoluteSector], dl
xor dx, dx
div word[bpbHeadsPerCylinder]
mov byte[absoluteHead], dl
mov byte[absoluteTrack], al
ret
main:
cli
mov ax, 0x07C0 ;0x7C0*2^4 = 0x7C00
mov ds, ax ;setup segment registers
mov es, ax
mov fs, ax
mov gs, ax
;create stack
mov ax, 0x0000
mov ss, ax
mov sp, 0xFFFF
sti
;display Starting
mov si, msgStart
call Print
;load root directory table
LOAD_ROOT:
;size of root directory = 32*(no of root entries)/(bytes per sector) SECTORS
xor cx, cx
xor dx, dx
mov ax, 0x0020
mul word[bpbRootEntries]
div word[bpbBytesPerSector]
xchg ax, cx ;size of root in cx
;location root directory = reserved sectors + (no of FATS * sectors per FAT)
mov al, byte [bpbNumberOfFATs]
mul word [bpbSectorsPerFAT]
add ax, word[bpbReservedSectors]
mov word [datasector], ax
add word [datasector], cx ;start of data sector
;read root directory into memory 0x7C0:0x0200 = 7C00+0200
mov bx, 0x0200
call ReadSectors
;find stage2 boot loader
mov cx, word[bpbRootEntries]
mov di, 0x0200 ;address of root table in memory
.LOOP:
push cx
mov cx, 0x000B ;11 character name
mov si, ImageName ;Image name
push di
rep cmpsb
pop di
je LOAD_FAT
pop cx
add di, 0x0020 ;next entry in root table
loop .LOOP
jmp FAILURE
LOAD_FAT:
;save starting cluster of boot image
mov dx, word[di+0x001A]
mov word[cluster], dx
;compute size of FAT and store in cx = no of FAT * sectors per FAT
xor ax, ax
mov al, byte[bpbNumberOfFATs]
mul word[bpbSectorsPerFAT]
mov cx, ax
;location of FAT in ax = no of reserved Sectors
mov ax, word[bpbReservedSectors]
;read FAT in memory at 0x7C0:0x0200
mov bx, 0x0200
call ReadSectors
;load image file into memory at 0050:0000 => 0x500)
mov ax, 0x0050
mov es, ax
mov bx, 0x0000
push bx
LOAD_IMAGE:
mov ax, word[cluster]
pop bx
call ClusterLBA
xor cx, cx
mov cl, byte[bpbSectorsPerCluster]
call ReadSectors
push bx
;compute next cluster, remember cluster entries are of 12 bits = 3/2 bytes
mov ax, word[cluster]
mov cx, ax
mov dx, ax
shr dx, 0x0001 ;devide by 2
add cx, dx ;equals to 3/2*cluster number
mov bx, 0x0200 ;location of FAT in memory
add bx, cx ;we moved 3/2*cluster no bytes from start
mov dx, word[bx] ;read 2 bytes in dx
test ax, 0x0001 ;if this was odd cluster => lower 12 bits, else =>higher 12 bits will be used
jnz .ODD_CLUSTER
.EVEN_CLUSTER:
and dx, 0000111111111111b
jmp .DONE
.ODD_CLUSTER:
shr dx, 0x0004
.DONE:
mov word[cluster], dx ;new cluster location
cmp dx, 0x0FF0 ;if this was last cluster
jb LOAD_IMAGE
DONE:
mov si, msgStageTwo
call Print
push word 0x0050 ;segment address
push word 0x0000 ;offset in segment
retf ;far return, both of the above value will be used
FAILURE:
mov si, msgFailure
call Print
mov ah, 0x00
int 0x16 ;wait for key press
int 0x19 ;reboot
absoluteSector db 0x00
absoluteHead db 0x00
absoluteTrack db 0x00
datasector dw 0x0000
cluster dw 0x0000
ImageName db "KRNLDR SYS" ;must be 11 bytes
msgStart db 0x0D,0x0A, "Boot Loader starting (0x7c00)....", 0x0D, 0x0A, 0x00
msgStageTwo db "Jumping to stage2 (0x500)", 0x0D, 0x0A, 0x0D, 0x0A, 0x00
msgFailure db 0x0D, 0x0A, "ERROR : Press Key to Reboot", 0x0A, 0x00
times 510-($-$$) db 0
dw 0xAA55 ;boot signature
我正在尝试在内存地址 0x500 处查找并加载第二阶段引导加载程序。似乎第二阶段没有在 0x500 加载。Bochs 刚刚在打印“跳转到第二阶段”后挂起（在跳转到第二阶段之前打印调用）。这是bochs日志：
00000000000i[ ] Bochs x86 Emulator 2.6
00000000000i[ ] Built from SVN snapshot on September 2nd, 2012
00000000000i[ ] System configuration
00000000000i[ ] processors: 1 (cores=1, HT threads=1)
00000000000i[ ] A20 line support: yes
00000000000i[ ] IPS is set to 4000000
00000000000i[ ] CPU configuration
00000000000i[ ] level: 6
00000000000i[ ] SMP support: no
00000000000i[ ] APIC support: xapic
00000000000i[ ] FPU support: yes
00000000000i[ ] MMX support: yes
00000000000i[ ] 3dnow! support: no
00000000000i[ ] SEP support: yes
00000000000i[ ] SSE support: sse2
00000000000i[ ] XSAVE support: no
00000000000i[ ] AES support: no
00000000000i[ ] MOVBE support: no
00000000000i[ ] ADX support: no
00000000000i[ ] x86-64 support: yes
00000000000i[ ] 1G paging support: no
00000000000i[ ] MWAIT support: yes
00000000000i[ ] AVX support: no
00000000000i[ ] VMX support: 1
00000000000i[ ] Optimization configuration
00000000000i[ ] RepeatSpeedups support: yes
00000000000i[ ] Fast function calls: yes
00000000000i[ ] Handlers Chaining speedups: no
00000000000i[ ] Devices configuration
00000000000i[ ] NE2000 support: yes
00000000000i[ ] PCI support: yes, enabled=yes
00000000000i[ ] SB16 support: yes
00000000000i[ ] USB support: yes
00000000000i[ ] VGA extension support: vbe cirrus
00000000000i[MEM0 ] allocated memory at 0x7f8a9189c010. after alignment, vector=0x7f8a9189d000
00000000000i[MEM0 ] 32.00MB
00000000000i[MEM0 ] mem block size = 0x00100000, blocks=32
00000000000i[MEM0 ] rom at 0xfffe0000/131072 ('/usr/share/bochs/BIOS-bochs-latest')
00000000000i[ ] lt_dlhandle is 0x3fb0540
00000000000i[PLGIN] loaded plugin libbx_hdimage.so
00000000000i[ ] lt_dlhandle is 0x3fb0ed0
00000000000i[PLGIN] loaded plugin libbx_pci.so
00000000000i[ ] lt_dlhandle is 0x3fb1a50
00000000000i[PLGIN] loaded plugin libbx_pci2isa.so
00000000000i[ ] lt_dlhandle is 0x3fb2460
00000000000i[PLGIN] loaded plugin libbx_acpi.so
00000000000i[ ] lt_dlhandle is 0x3fb2e60
00000000000i[PLGIN] loaded plugin libbx_cmos.so
00000000000i[ ] lt_dlhandle is 0x3fb37a0
00000000000i[PLGIN] loaded plugin libbx_dma.so
00000000000i[ ] lt_dlhandle is 0x3fb4230
00000000000i[PLGIN] loaded plugin libbx_pic.so
00000000000i[ ] lt_dlhandle is 0x3fb4ad0
00000000000i[PLGIN] loaded plugin libbx_pit.so
00000000000i[ ] lt_dlhandle is 0x3fb5500
00000000000i[PLGIN] loaded plugin libbx_floppy.so
00000000000i[ ] lt_dlhandle is 0x3fb60f0
00000000000i[PLGIN] loaded plugin libbx_vga.so
00000000000i[ ] lt_dlhandle is 0x3fb6880
00000000000i[PLGIN] loaded plugin libbx_ioapic.so
00000000000i[ ] lt_dlhandle is 0x3fb72c0
00000000000i[PLGIN] loaded plugin libbx_keyboard.so
00000000000i[ ] lt_dlhandle is 0x3fb7b60
00000000000i[PLGIN] loaded plugin libbx_harddrv.so
00000000000i[ ] lt_dlhandle is 0x3fc9c50
00000000000i[PLGIN] loaded plugin libbx_pci_ide.so
00000000000i[PLGIN] init_dev of 'pci' plugin device by virtual method
00000000000i[PCI ] 440FX Host bridge present at device 0, function 0
00000000000i[PLGIN] init_dev of 'pci2isa' plugin device by virtual method
00000000000i[PCI ] PIIX3 PCI-to-ISA bridge present at device 1, function 0
00000000000i[PLGIN] init_dev of 'cmos' plugin device by virtual method
00000000000i[CMOS ] Using local time for initial clock
00000000000i[CMOS ] Setting initial clock to: Fri Jan 5 20:53:22 2018 (time0=1515165802)
00000000000i[PLGIN] init_dev of 'dma' plugin device by virtual method
00000000000i[DMA ] channel 4 used by cascade
00000000000i[PLGIN] init_dev of 'pic' plugin device by virtual method
00000000000i[PLGIN] init_dev of 'pit' plugin device by virtual method
00000000000i[PLGIN] init_dev of 'floppy' plugin device by virtual method
00000000000i[DMA ] channel 2 used by Floppy Drive
00000000000e[FDD ] cannot determine media geometry, trying to use defaults
00000000000i[FDD ] fd0: '/dev/loop0' ro=0, h=2,t=80,spt=18
00000000000i[PLGIN] init_dev of 'vga' plugin device by virtual method
00000000000i[MEM0 ] Register memory access handlers: 0x00000000000a0000 - 0x00000000000bffff
00000000000i[VGA ] interval=200000
00000000000i[MEM0 ] Register memory access handlers: 0x00000000e0000000 - 0x00000000e0ffffff
00000000000i[BXVGA] VBE Bochs Display Extension Enabled
00000000000i[XGUI ] test_alloc_colors: 16 colors available out of 16 colors tried
00000000000i[XGUI ] font 8 wide x 16 high, display depth = 24
00000000000i[MEM0 ] rom at 0xc0000/41472 ('/usr/share/bochs/VGABIOS-lgpl-latest')
00000000000i[PLGIN] init_dev of 'acpi' plugin device by virtual method
00000000000i[PCI ] ACPI Controller present at device 1, function 3
00000000000i[PLGIN] init_dev of 'ioapic' plugin device by virtual method
00000000000i[IOAP ] initializing I/O APIC
00000000000i[MEM0 ] Register memory access handlers: 0x00000000fec00000 - 0x00000000fec00fff
00000000000i[PLGIN] init_dev of 'keyboard' plugin device by virtual method
00000000000i[KBD ] will paste characters every 1000 keyboard ticks
00000000000i[PLGIN] init_dev of 'harddrv' plugin device by virtual method
00000000000i[HD ] Using boot sequence floppy, none, none
00000000000i[HD ] Floppy boot signature check is enabled
00000000000i[PLGIN] init_dev of 'pci_ide' plugin device by virtual method
00000000000i[PCI ] PIIX3 PCI IDE controller present at device 1, function 1
00000000000i[PLGIN] init_dev of 'unmapped' plugin device by virtual method
00000000000i[PLGIN] init_dev of 'biosdev' plugin device by virtual method
00000000000i[PLGIN] init_dev of 'speaker' plugin device by virtual method
00000000000i[PLGIN] init_dev of 'extfpuirq' plugin device by virtual method
00000000000i[PLGIN] init_dev of 'parallel' plugin device by virtual method
00000000000i[PAR ] parallel port 1 at 0x0378 irq 7
00000000000i[PLGIN] init_dev of 'serial' plugin device by virtual method
00000000000i[SER ] com1 at 0x03f8 irq 4
00000000000i[PLGIN] init_dev of 'gameport' plugin device by virtual method
00000000000i[PLGIN] init_dev of 'iodebug' plugin device by virtual method
00000000000i[PLGIN] register state of 'pci' plugin device by virtual method
00000000000i[PLGIN] register state of 'pci2isa' plugin device by virtual method
00000000000i[PLGIN] register state of 'cmos' plugin device by virtual method
00000000000i[PLGIN] register state of 'dma' plugin device by virtual method
00000000000i[PLGIN] register state of 'pic' plugin device by virtual method
00000000000i[PLGIN] register state of 'pit' plugin device by virtual method
00000000000i[PLGIN] register state of 'floppy' plugin device by virtual method
00000000000i[PLGIN] register state of 'vga' plugin device by virtual method
00000000000i[PLGIN] register state of 'unmapped' plugin device by virtual method
00000000000i[PLGIN] register state of 'biosdev' plugin device by virtual method
00000000000i[PLGIN] register state of 'speaker' plugin device by virtual method
00000000000i[PLGIN] register state of 'extfpuirq' plugin device by virtual method
00000000000i[PLGIN] register state of 'parallel' plugin device by virtual method
00000000000i[PLGIN] register state of 'serial' plugin device by virtual method
00000000000i[PLGIN] register state of 'gameport' plugin device by virtual method
00000000000i[PLGIN] register state of 'iodebug' plugin device by virtual method
00000000000i[PLGIN] register state of 'acpi' plugin device by virtual method
00000000000i[PLGIN] register state of 'ioapic' plugin device by virtual method
00000000000i[PLGIN] register state of 'keyboard' plugin device by virtual method
00000000000i[PLGIN] register state of 'harddrv' plugin device by virtual method
00000000000i[PLGIN] register state of 'pci_ide' plugin device by virtual method
00000000000i[SYS ] bx_pc_system_c::Reset(HARDWARE) called
00000000000i[CPU0 ] cpu hardware reset
00000000000i[APIC0] allocate APIC id=0 (MMIO enabled) to 0x00000000fee00000
00000000000i[CPU0 ] CPUID[0x00000000]: 00000002 756e6547 6c65746e 49656e69
00000000000i[CPU0 ] CPUID[0x00000001]: 00000633 00010800 00002028 1fcbfbff
00000000000i[CPU0 ] CPUID[0x00000002]: 00410601 00000000 00000000 00000000
00000000000i[CPU0 ] CPUID[0x80000000]: 80000008 00000000 00000000 00000000
00000000000i[CPU0 ] CPUID[0x80000001]: 00000000 00000000 00000101 2a100000
00000000000i[CPU0 ] CPUID[0x80000002]: 20202020 20202020 20202020 6e492020
00000000000i[CPU0 ] CPUID[0x80000003]: 286c6574 50202952 69746e65 52286d75
00000000000i[CPU0 ] CPUID[0x80000004]: 20342029 20555043 20202020 00202020
00000000000i[CPU0 ] CPUID[0x80000005]: 01ff01ff 01ff01ff 40020140 40020140
00000000000i[CPU0 ] CPUID[0x80000006]: 00000000 42004200 02008140 00000000
00000000000i[CPU0 ] CPUID[0x80000007]: 00000000 00000000 00000000 00000000
00000000000i[CPU0 ] CPUID[0x80000008]: 00003028 00000000 00000000 00000000
00000000000i[PLGIN] reset of 'pci' plugin device by virtual method
00000000000i[PLGIN] reset of 'pci2isa' plugin device by virtual method
00000000000i[PLGIN] reset of 'cmos' plugin device by virtual method
00000000000i[PLGIN] reset of 'dma' plugin device by virtual method
00000000000i[PLGIN] reset of 'pic' plugin device by virtual method
00000000000i[PLGIN] reset of 'pit' plugin device by virtual method
00000000000i[PLGIN] reset of 'floppy' plugin device by virtual method
00000000000i[PLGIN] reset of 'vga' plugin device by virtual method
00000000000i[PLGIN] reset of 'acpi' plugin device by virtual method
00000000000i[PLGIN] reset of 'ioapic' plugin device by virtual method
00000000000i[PLGIN] reset of 'keyboard' plugin device by virtual method
00000000000i[PLGIN] reset of 'harddrv' plugin device by virtual method
00000000000i[PLGIN] reset of 'pci_ide' plugin device by virtual method
00000000000i[PLGIN] reset of 'unmapped' plugin device by virtual method
00000000000i[PLGIN] reset of 'biosdev' plugin device by virtual method
00000000000i[PLGIN] reset of 'speaker' plugin device by virtual method
00000000000i[SPEAK] Using /dev/console for output
00000000000i[PLGIN] reset of 'extfpuirq' plugin device by virtual method
00000000000i[PLGIN] reset of 'parallel' plugin device by virtual method
00000000000i[PLGIN] reset of 'serial' plugin device by virtual method
00000000000i[PLGIN] reset of 'gameport' plugin device by virtual method
00000000000i[PLGIN] reset of 'iodebug' plugin device by virtual method
00000000000i[XGUI ] Mouse capture off
00000000000i[XGUI ] Mouse capture off
00000000000i[MEM0 ] allocate_block: block=0x0 used 0x1 of 0x20
00000004661i[BIOS ] $Revision: 11318 $ $Date: 2012-08-06 19:59:54 +0200 (Mo, 06. Aug 2012) $
00000319051i[KBD ] reset-disable command received
00000321813i[BIOS ] Starting rombios32
00000322255i[BIOS ] Shutdown flag 0
00000322852i[BIOS ] ram_size=0x02000000
00000323280i[BIOS ] ram_end=32MB
00000363809i[BIOS ] Found 1 cpu(s)
00000377990i[BIOS ] bios_table_addr: 0x000fa438 end=0x000fcc00
00000705785i[PCI ] 440FX PMC write to PAM register 59 (TLB Flush)
00001033717i[P2I ] PCI IRQ routing: PIRQA# set to 0x0b
00001033741i[P2I ] PCI IRQ routing: PIRQB# set to 0x09
00001033765i[P2I ] PCI IRQ routing: PIRQC# set to 0x0b
00001033789i[P2I ] PCI IRQ routing: PIRQD# set to 0x09
00001033799i[P2I ] write: ELCR2 = 0x0a
00001034578i[BIOS ] PIIX3/PIIX4 init: elcr=00 0a
00001042258i[BIOS ] PCI: bus=0 devfn=0x00: vendor_id=0x8086 device_id=0x1237 class=0x0600
00001044537i[BIOS ] PCI: bus=0 devfn=0x08: vendor_id=0x8086 device_id=0x7000 class=0x0601
00001046655i[BIOS ] PCI: bus=0 devfn=0x09: vendor_id=0x8086 device_id=0x7010 class=0x0101
00001046884i[PIDE ] new BM-DMA address: 0xc000
00001047504i[BIOS ] region 4: 0x0000c000
00001049538i[BIOS ] PCI: bus=0 devfn=0x0b: vendor_id=0x8086 device_id=0x7113 class=0x0680
00001049768i[ACPI ] new irq line = 11
00001049782i[ACPI ] new irq line = 9
00001049809i[ACPI ] new PM base address: 0xb000
00001049823i[ACPI ] new SM base address: 0xb100
00001049851i[PCI ] setting SMRAM control register to 0x4a
00001213945i[CPU0 ] Enter to System Management Mode
00001213945i[CPU0 ] enter_system_management_mode: temporary disable VMX while in SMM mode
00001213955i[CPU0 ] RSM: Resuming from System Management Mode
00001377976i[PCI ] setting SMRAM control register to 0x0a
00001392878i[BIOS ] MP table addr=0x000fa510 MPC table addr=0x000fa440 size=0xc8
00001394693i[BIOS ] SMBIOS table addr=0x000fa520
00001394744i[MEM0 ] allocate_block: block=0x1f used 0x2 of 0x20
00001397672i[BIOS ] Firmware waking vector 0x1ff00cc
00001402531i[BIOS ] ACPI tables: RSDP addr=0x000fa640 ACPI DATA addr=0x01ff0000 size=0x1f22
00001402568i[PCI ] 440FX PMC write to PAM register 59 (TLB Flush)
00001403299i[BIOS ] bios_table_cur_addr: 0x000fa664
00001530917i[VBIOS] VGABios $Id: vgabios.c,v 1.75 2011/10/15 14:07:21 vruppert Exp $
00001530988i[BXVGA] VBE known Display Interface b0c0
00001531020i[BXVGA] VBE known Display Interface b0c5
00001533945i[VBIOS] VBE Bios $Id: vbe.c,v 1.64 2011/07/19 18:25:05 vruppert Exp $
00001600003i[XGUI ] charmap update. Font Height is 16
00014040953i[BIOS ] Booting from 0000:7c00
00065146879i[ ] dbg: Quit
00065146879i[CPU0 ] CPU is in real mode (active)
00065146879i[CPU0 ] CS.mode = 16 bit
00065146879i[CPU0 ] 00065146879i[XGUI ] Mouse capture off
00065146879i[CTRL ] quit_sim called with exit code 0
这是bochs的配置文件：
romimage: file="/usr/share/bochs/BIOS-bochs-latest"
vgaromimage: file ="/usr/share/bochs/VGABIOS-lgpl-latest"
floppya: 1_44=/dev/loop0, status=inserted
display_library: x, options="gui_debug"
log: bochsout.txt
这就是我创建和安装 FAT12 软盘的方式
dd if=/dev/zero of=myfloppy.img bs=512 count=2880
losetup /dev/loop0 myfloppy.img
mkdosfs -F 12 /dev/loop0
mount /dev/loop0 myfloppy -t msdos -o "fat=12"
dd if=LOADER.SYS of=/dev/loop0
cp KRNLDR.SYS myfloppy
我的引导加载程序在虚拟盒中也可以正常工作，下面是一张图片
最后一行“准备加载操作系统”是第二阶段引导加载程序的一部分。但它无法在bochs中工作，可能是什么原因？
最后是第二阶段引导加载程序（如果需要）：
;*********************************************
; Stage2.asm
; - Second Stage Bootloader
;
; Operating Systems Development Series
;*********************************************
org 0x0 ; offset to 0, we will set segments later
bits 16 ; we are still in real mode
; we are loaded at linear address 0x10000
jmp main ; jump to main
;*************************************************;
; Prints a string
; DS=>SI: 0 terminated string
;************************************************;
Print:
lodsb ; load next byte from string from SI to AL
or al, al ; Does AL=0?
jz PrintDone ; Yep, null terminator found-bail out
mov ah, 0eh ; Nope-Print the character
int 10h
jmp Print ; Repeat until null terminator found
PrintDone:
ret ; we are done, so return
;*************************************************;
; Second Stage Loader Entry Point
;************************************************;
main:
cli ; clear interrupts
push cs ; Insure DS=CS
pop ds
mov si, Msg
call Print
cli ; clear interrupts to prevent triple faults
hlt ; hault the syst
;*************************************************;
; Data Section
;************************************************;
Msg db "Preparing to load operating system...",13,10,0