演示任务切换的实例（实例五）－－RadASM编译

来源：互联网发布：微信业务域名是什么编辑：程序博客网时间：2024/06/05 05:05

以下代码用RadASM编译(其实也是用MASM编译的)，BOCHS调试成功。

红色字体是经过增加或修改的，否则不能编译成功，相信会节省初学者不少精力。

INCLUDE 386SCD.INC
;----------------------------------------------------------------------------

GDTSEG SEGMENT PARA USE16 ;全局描述符表数据段(16位)
;----------------------------------------------------------------------------
;全局描述符表
GDT LABEL BYTE
;空描述符
DUMMY DESCRIPTOR <>
;规范段描述符及选择子
Normal DESCRIPTOR <0ffffh,0,0,ATDW,0>
Normal_Sel = Normal-GDT
;视频缓冲区段描述符(DPL=3)及选择子
EFFGDT LABEL BYTE
;演示任务的任务状态段描述符及选择子
DemoTSS DESCRIPTOR <DemoTSSLen-1,DemoTSSSeg,,AT386TSS,>
DemoTSS_Sel = DemoTSS-GDT

;演示任务的局部描述符表段的描述符及选择子
DemoLDTab DESCRIPTOR <DemoLDTLen-1,DemoLDTSeg,,ATLDT,>
DemoLDT_Sel = DemoLDTab-GDT

;临时任务的任务状态段描述符及选择子
TempTSS DESCRIPTOR <TempTSSLen-1,TempTSSSeg,,AT386TSS+DPL2,>
TempTSS_Sel = TempTSS-GDT
;临时代码段描述符及选择子
TempCode DESCRIPTOR <0ffffh,TempCodeSeg,,ATCE,>
TempCode_Sel = TempCode-GDT

;子程序代码段描述符及选择子
SubR DESCRIPTOR <SubRLen32-1,SubRSeg,,ATCE+D32,>
SubR_Sel = SubR-GDT+RPL3

; VIDEOBUFF DESCRIPTOR <0ffffh,8000h,0bh, ATDW+DPL3,>
VIDEOBUFF DESCRIPTOR<0FFFFH,0,0,0F00H+ATDW+DPL3,0>
Video_SEL = VIDEOBUFF - GDT
;----------------------------------------------------------------------------

GDNUM = ($-EFFGDT)/(SIZE DESCRIPTOR) ;需处理基地址的描述符个数
GDTLen = $-GDT ;全局描述符表长度

;----------------------------------------------------------------------------
GDTSEG ENDS ;全局描述符表段定义结束
;----------------------------------------------------------------------------
DemoLDTSeg SEGMENT PARA USE16 ;局部描述符表数据段(16位)

;----------------------------------------------------------------------------
DemoLDT LABEL BYTE ;局部描述符表
;0级堆栈段描述符(32位段)及选择子
DemoStack0 DESCRIPTOR <DemoStack0Len-1,DemoStack0Seg,,ATDW+D32,>

DemoStack0_Sel = DemoStack0-DemoLDT+TIL
;2级堆栈段描述符(32位段)及选择子
DemoStack2 DESCRIPTOR <DemoStack2Len-1,DemoStack2Seg,,ATDW+DPL2+D32,>

DemoStack2_Sel = DemoStack2-DemoLDT+TIL+RPL2
;演示任务代码段描述符(32位段,DPL=2)及选择子
DemoCode DESCRIPTOR <DemoCodeLen32-1,DemoCodeSeg,,ATCE+DPL2+D32,>

DemoCode_Sel = DemoCode-DemoLDT+TIL+RPL2
;演示任务数据段描述符(32位段,DPL=3)及选择子
DemoData DESCRIPTOR <DemoDataLen32-1,DemoDataSeg,,ATDW+DPL3+D32,>

DemoData_Sel = DemoData-DemoLDT+TIL
;把LDT作为普通数据段描述的描述符(DPL=2)及选择子
ToDLDT DESCRIPTOR <DemoLDTLen-1,DemoLDTSeg,,ATDW+DPL2,>

ToDLDT_Sel = ToDLDT-DemoLDT+TIL
;把TSS作为普通数据段描述的描述符(DPL=2)及选择子
ToTTSS DESCRIPTOR <TempTSSLen-1,TempTSSSeg,,ATDW+DPL2,>

ToTTSS_Sel = ToTTSS-DemoLDT+TIL
;----------------------------------------------------------------------------
DemoLDNum = ($-DemoLDT)/(SIZE DESCRIPTOR) ;需处理基地址的LDT描述符数

;----------------------------------------------------------------------------
;指向子程序SubRB代码段的调用门(DPL=3)及选择子
ToSubR GATE <SubRB32,SubR_Sel,0,AT386CGAT+DPL3,0>
ToSubR_Sel = ToSubR-DemoLDT+TIL+RPL2
;指向临时任务Temp的任务门(DPL=3)及选择子

ToTempT GATE <0,TempTSS_Sel,0,ATTASKGAT+DPL3,0>
ToTempT_Sel = ToTempT-DemoLDT+TIL

;----------------------------------------------------------------------------
DemoLDTLen = $-DemoLDT
;----------------------------------------------------------------------------
DemoLDTSeg ENDS ;局部描述符表段定义结束
;----------------------------------------------------------------------------
DemoTSSSeg SEGMENT PARA USE16 ;任务状态段TSS

;----------------------------------------------------------------------------
DD 0 ;链接字
DD DemoStack0Len ;0级堆栈指针
DW DemoStack0_Sel,0 ;0级堆栈选择子

DD 0 ;1级堆栈指针(实例不使用)
DW ?,0 ;1级堆栈选择子(实例不使用)

DD DemoStack2Len ;2级堆栈指针
DW DemoStack2_Sel,0 ;2级堆栈选择子
DD 0 ;CR3
DW DemoBegin32,0 ;EIP

DD 0 ;EFLAGS
DD 0 ;EAX
DD 0 ;ECX

DD 0 ;EDX
DD 0 ;EBX
DD DemoStack2Len ;ESP

DD 0 ;EBP
DD 0 ;ESI
DD 0b8000h ;EDI
DW Video_SEL,0 ;ES
DW DemoCode_Sel,0 ;CS

DW DemoStack2_Sel,0 ;SS
DW DemoData_Sel,0 ;DS

DW ToDLDT_Sel,0 ;FS
DW ToTTSS_Sel,0 ;GS

DW DemoLDT_Sel,0 ;LDTR
DW 0 ;调试陷阱标志
DW $+2 ;指向I/O许可位图

DB 0ffh ;I/O许可位图结束标志
DemoTSSLen = $ - DemoTSSSeg
DemoTSSSeg ENDS ;任务状态段TSS结束

;----------------------------------------------------------------------------

DemoStack0Seg SEGMENT PARA USE32 ;演示任务0级堆栈段(32位段)
DemoStack0Len = 1024
DB DemoStack0Len DUP(0)

DemoStack0Seg ENDS ;演示任务0级堆栈段结束
;----------------------------------------------------------------------------
DemoStack2Seg SEGMENT PARA USE32 ;演示任务2级堆栈段(32位段)
DemoStack2Len = 512

DB DemoStack2Len DUP(0)
DemoStack2Seg ENDS ;演示任务2级堆栈段结束
;----------------------------------------------------------------------------
DemoDataSeg SEGMENT PARA USE32 ;演示任务数据段(32位段)

Message DB 'Value=',0
DemoDataLen32 equ this word
DemoDataLen = $ - DemoDataSeg
DemoDataSeg ENDS ;演示任务数据段结束

;----------------------------------------------------------------------------
SubRSeg SEGMENT PARA USE32 ;子程序代码段(32位)
ASSUME CS:SubRSeg
;----------------------------------------------------------------------------
SubRB32 equ this word
SubRB PROC FAR
push ebp
mov ebp,esp

pushad ;保护现场
mov esi,DWORD PTR [ebp+12] ;从0级栈中取出显示串偏移

mov ah,4ah ;设置显示属性
jmp SHORT SubR2
SubR1: stosw

SubR2: lodsb
or al,al
jnz SubR1
mov ah,4eh ;设置显示属性

mov edx,DWORD PTR [ebp+16] ;从0级栈中取出显示值

mov ecx,8
SubR3: rol edx,4
mov al,dl

call HToASCII
stosw
loop SubR3
popad
pop ebp

ret 8
SubRB ENDP
;----------------------------------------------------------------------------
HToASCII PROC
and al,0fh

add al,90h
daa
adc al,40h
daa
ret
HToASCII ENDP
SubRLen32 equ this word
SubRLen = $ - SubRSeg
SubRSeg ENDS ;子程序代码段结束

;----------------------------------------------------------------------------
DemoCodeSeg SEGMENT PARA USE32 ;演示任务的32位代码段
ASSUME CS:DemoCodeSeg

;----------------------------------------------------------------------------
DemoBegin32 equ this word
DemoBegin :
;把要复制的参数个数置入调用门
mov BYTE PTR fs:ToSubR.DCOUNT,2

;向2级堆栈中压入参数
push DWORD PTR gs:TempTask.TREIP
push OFFSET Message
;通过调用门调用SubRB

CALL32 ToSubR_Sel,0
;把指向规范数据段描述符的选择子填入临时任务TSS
ASSUME DS:TempTSSSeg
push gs

pop ds
mov ax,Normal_Sel
mov WORD PTR TempTask.TRDS,ax

mov WORD PTR TempTask.TRES,ax
mov WORD PTR TempTask.TRFS,ax

mov WORD PTR TempTask.TRGS,ax
mov WORD PTR TempTask.TRSS,ax

;通过任务门切换到临时任务
JUMP32 ToTempT_Sel,0
DemoCodeLen32 equ this word
DemoCodeLen = $ - DemoCodeSeg
DemoCodeSeg ENDS ;演示任务的32位代码段结束

;----------------------------------------------------------------------------
TempTSSSeg SEGMENT PARA USE16 ;临时任务的任务状态段TSS

TempTask TASKSS <>
DB 0ffh ;I/O许可位图结束标志
TempTSSLen = $
TempTSSSeg ENDS

;----------------------------------------------------------------------------
TempCodeSeg SEGMENT PARA USE16 ;临时任务的代码段
ASSUME CS:TempCodeSeg
;----------------------------------------------------------------------------

Virtual :
mov ax,TempTSS_Sel ;装载TR
ltr ax

JUMP16 DemoTSS_Sel,0 ;直接切换到演示任务
ToReal:
clts ;清任务切换标志
mov eax,cr0 ;准备返回实模式

and al,0fffffffeh
mov cr0,eax
JUMP16 <SEG Real>,<OFFSET Real>
TempCodeLEN = $ - TempCodeSeg

TempCodeSeg ENDS
;============================================================================
RDataSeg SEGMENT PARA USE16 ;实方式数据段

VGDTR PDESC <GDTLen-1,> ;GDT伪描述符
SPVar DW ? ;用于保存实方式下的SP
SSVar DW ? ;用于保存实方式下的SS

RDataSeg ENDS
;----------------------------------------------------------------------------
RCODESEG SEGMENT PARA USE16
ASSUME CS:RCODESEG,DS:RDataSeg,ES:RDataSeg

;----------------------------------------------------------------------------
Start :
;jmp $ ;bochs调试时使用，CTRL+C中断后，set $eip = 2 ,C运行即可。
mov ax,RDataSeg
mov ds,ax

cld
call INIT_GDT ;初始化全局描述符表GDT
mov ax,DemoLDTSeg
mov fs,ax

mov si,OFFSET DemoLDT
mov cx,DemoLDNum
call INIT_LDT ;初始化局部描述符表LDT

mov SSVar,ss
mov SPVar,sp
lgdt FWORD PTR VGDTR ;装载GDTR并切换到保护方式

cli
mov eax,cr0
or al,1

mov cr0,eax
JUMP16 <TempCode_Sel>,<OFFSET Virtual>
Real: mov ax,RDataSeg
mov ds,ax

lss sp,DWORD PTR SPVar ;又回到实方式
sti
mov ax,4c00h

int 21h

;----------------------------------------------------------------------------
;初始化全局描述表的子程序
;(1)把定义时预置的段值转移成32位段基地址并置入描述符内相应字段;初始化GDT中的描述符
;(2)初始化为GDTR准备的伪描述符 ;初始化GDT伪描述符
INIT_GDT PROC NEAR
PUSH DS
MOV AX,GDTSEG
MOV DS,AX
MOV CX,GDNUM ;GDNUM是初始化的描述符个数
MOV SI,OFFSET EFFGDT ;EFFGDT是开始偏移值
ASSUME SI:PTR DESCRIPTOR
INITG: MOV AX,[SI].BASEL ;取出预置的段值
MOVZX EAX,AX ;扩展到32位
SHL EAX,4
SHLD EDX,EAX,16 ;分解到2个16位寄存器
MOV [SI].BASEL,AX
MOV [SI].BASEM,DL ;置入描述符相应字段
MOV [SI].BASEH,DH
ADD SI,SIZE DESCRIPTOR ;调整到下一描述符
LOOP INITG
ASSUME SI:NOTHING
POP DS
;
MOV BX,16 ;初始化为GDTR准备的伪描述符
MOV AX,GDTSEG
MUL BX
MOV WORD PTR VGDTR.BASE,AX
MOV WORD PTR VGDTR.BASE+2,DX
ret
INIT_GDT endp
;
;初始化演示任务局部描述符的子程序
;把定义时预置的段值转换成32位段基地址并置入描述符内相应字段
;入口参数:FS:SI=第一个要初始化的描述符
; CX = 要初始化的描述符个数
INIT_LDT PROC
ASSUME SI:PTR DESCRIPTOR

ILDT: MOV AX,FS:[SI].BASEL
MOVZX EAX,AX
SHL EAX,4
SHLD EDX,EAX,16
MOV FS:[SI].BASEL,AX
MOV FS:[SI].BASEM,DL
MOV FS:[SI].BASEH,DH
ADD SI,SIZE DESCRIPTOR
LOOP ILDT
ASSUME SI:NOTHING
ret
INIT_LDT endp
RCODESEG ENDS
END Start

运行结果：见图

386SCD.INC

;..........................
.386P
;存储段和系统段描述符
DESCRIPTOR STRUC
LIMITL DW 0
BASEL DW 0
BASEM DB 0
ATTRIBUTES DW 0
BASEH DB 0

DESCRIPTOR ENDS
;.........................
;门描述符
GATE STRUC
OFFSETL DW 0
SELECTOR DW 0
DCOUNT DB 0
GTYPE DB 0
OFFSETH DW 0
GATE ENDS

;.........................
;伪描述符
PDESC STRUC
LIMIT DW 0
BASE DD 0
PDESC ENDS
;.........................

;TASKSS任务状态段内容
TASKSS STRUC
TRLINK DW ?,0
TRESP0 DD ?
TRSS0 DW ?,0
TRESP1 DD ?
TRSS1 DW ?,0
TRESP2 DD ?
TRSS2 DW ?,0
TRCR3 DD ?
TREIP DD ?
TREFLAG DW ?,?
TREAX DD ?
TRECX DD ?
TREDX DD ?
TREBX DD ?
TRESP DD ?
TREBP DD ?
TRESI DD ?
TREDI DD ?
TRES DW ?,0
TRCS DW ?,0
TRSS DW ?,0
TRDS DW ?,0
TRFS DW ?,0
TRGS DW ?,0
TRLDT DW ?,0
TRFLAG DW 0
TRIOMAP DW $+2
TASKSS ENDS
;..........................
;存储段描述符类型值说明
ATDR =90H
ATDW =92H
ATDWA =93H
ATCE =98H
ATCER =9AH
ATCCO =9CH
ATCCOR =9EH
;系统段描述符和门描述符类型值说明
ATLDT =82H
ATTASKGAT =85H
AT386TSS =89H
AT386CGAT =8CH
AT386IGAT =8EH
AT386TGAT =8FH
;DPL和RPL值说明
;..........................

DPL1 =20H
DPL2 =40H
DPL3 =60H
RPL1 =01H
RPL2 =02H
RPL3 =03H
IOPL1 =1000H
IOPL2 =2000H
IOPL3 =3000H
;.............................

;其它常量说明
D32 =4000H
TIL =04H
VMFL =0002H
IFL =0200H
;.............................

;段间转移及段间调用宏
JUMP32 MACRO selector,offsetv
DB 0EAH
DW offsetv
DW 0
DW selector
ENDM
CALL32 MACRO selector,offsetv
DB 09AH
DW offsetv
DW 0
DW selector
ENDM

JUMP16 MACRO selector,offsetv
DB 0EAH
DW offsetv
DW selector
ENDM
CALL16 MACRO selector,offsetv
DB 9AH
DW offsetv
DW selector
ENDM

;................................