自己编写操作系统的笔记6

 郁闷死了，花了好几天写出的代码，编译也通过了，但是运行时会使dosbox当掉。通过debug，发现问题发生在跳入32位代码段的地方。下午继续研究吧。

Title protect2.asm include protect.inc .386p GDTseg segment para use16 'GDT' ;org OriginStart GDTBegin LABEL BYTE Dummy Descriptor<> ;不需要再设置 Normal Descriptor <0FFFFH,,,DA_DRW,> ;不需要再设置 Normal_sel =Normal-GDTBegin Code16A Descriptor<0FFFFH,,,DA_CR,> ;需要再设置 Code16A_sel =Code16A-GDTBegin Code16B Descriptor<0FFFFH,,,DA_CR,> ;需要再设置 Code16B_sel =Code16A-GDTBegin Code32 Descriptor<0FFFFH,,,DA_CR,> ;需要再设置 Code32_sel =Code16A-GDTBegin Vedio Descriptor<0FFFFH,0,80h,DA_DRW,0Bh> ;不需要再设置 Vedio_sel =Vedio-GDTBegin Stack Descriptor<0AH,,,DA_DRWA + DA_32,> ;需要再设置 Stack_sel =Stack-GDTBegin DataTest Descriptor<0FFFFH,0,0,DA_DRW,50h> ;不需要再设置 DataTest_sel=DataTest-GDTBegin GDTLEN =$-GDTBegin GDTPTR fdesc<GDTLEN-1,offset GDTBegin> ;GDTseglenth =$-GDTBegin GDTseg ends codestart segment PARA use16 'code16' assume cs:codestart,ds:GDTseg Begin: mov ax,GDTseg mov ds,ax SetDescBase <codestart>,<Code16A> ;设置Code16A的描述符 SetDescBase <codereturn16>,<Code16B> ;设置Code16A的描述符 SetDescBase <code32seg>,<Code32> ;设置Code16A的描述符 SetDescBase <datafortest>,<DataTest> ;设置Code16A的描述符 SetDescBase <stackseg>,<Stack> ;设置Code16A的描述符 lgdt Fword PTR GDTPTR cli OpenA20 SetCR0ToProtect Jump16 <code32_sel>,<offset code32Begin> ;跳转到 ;codestartlenth =$-Begin codestart ends code32seg segment para use16 'code32' assume cs:code32seg code32Begin: mov ax,Code32_sel mov cs,ax mov ax,DataTest_sel mov ds,ax mov ax,Stack_sel mov ss,ax mov ax,Vedio_sel mov gs,ax ;-------------------------------------------------------------------- call TestRead call TestWrite call TestRead ;-------------------------------------------------------------------- mov ax,Normal_sel mov es,ax mov fs,ax mov gs,ax mov ss,ax mov esp,10 mov eax,cr0 and eax,0FFFFFFFEH mov cr0,eax JUMP16 <SEG codereturn16>,<offset return> TestRead proc far xor esi,esi mov ecx,8 testread1: mov al,es:[esi] call DispAL inc esi loop testread1 call DispReturn ret TestRead endp TestWrite proc far push esi push edi xor esi,esi xor edi,edi mov esi,offsetPMMesssage cld TestWrite1: lodsb test al,al jz TestWrite2 mov es:[edi],al inc edi jmp TestWrite1 TestWrite2: pop edi pop esi ret TestWrite endp ;--------------------------------------------------------- DispAL proc far push ecx push edx mov ah,0ch mov dl,al shr al,4 mov ecx,2 DispALStart: and al,01111b cmp al,9 ja dispal1 add al,'0' jmp dispal2 dispal1: sub al,0AH add al,'A' dispal2: mov gs:[edi],ax add edi,2 mov al,dl loop DispALStart add edi,2 pop edx pop ecx ret DispAL endp DispReturn proc far push eax push ebx mov eax,edi mov bl,160 div bl and eax,0FFh inc eax mov bl,160 mul bl mov edi,eax pop ebx pop eax DispReturn endp ;code32seglenth =$-code32Begin code32seg ends codereturn16 segment para use16 'code16' assume cs:codereturn16 return: sti mov ax,4c00h int 21h codereturnlenth =$-return codereturn16 ends datafortest segment para use32 'data' Data label byte SPValueInRealMode dw 0 PMMessage db 'In protect mode now.^^',0 offsetPMMesssage equ PMMessage-seg PMMessage StrTest db 'ABCDEFGHIJKLMNOPQRSTUVWXYZ',0 OffsetStrTest equ $-seg StrTest DataLenth =$-data datafortest ends stackseg segment para use16 'data' db 10 dup(0) ; Free EQU (BootSectorLenth-2-10)-GDTseglenth-codestartlenth-codereturnlenth-code32seglenth-DataLenth ; if Free LT 0 ; %out FATAL PROBLEM:boot sector is too large ; endif ; org OriginStart + (BootSectorLenth-2) ; db 55h,0aah stackseg ends end begin

 

 GDTPTR  fdesc<GDTLEN-1,offset GDTBegin>这里是错的，offset GDTBegin只是偏移，又不是地址

现在留空，然后在 lgdt Fword PTR GDTPTR前加入

 mov ax,GDTseg
 mov bx,16
 mul bx
 mov word ptr GDTPTR.base,ax
 mov word ptr GDTPTR.base+2,dx

这样应该可以了。不过还没调试，因为这里没有dosbox可以用~