asm5.asm

用纯C写的基于x86结构的保护模式相关操作

;名称:ASM5.ASM
;功能:演示任务切换和任务内有特权级变换的转移
;编译:TASM ASM5.ASM
;链接:TLINK /32 ASM5.OBJ
;----------------------------------------------------------------------------
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           Desc    <>
                ;规范段描述符及选择子
Normal          Desc    <0ffffh,,,ATDW,,>
Normal_Sel      =       Normal-GDT
                ;视频缓冲区段描述符(DPL=3)及选择子
VideoBuf        Desc    <0ffffh,8000h,0bh,ATDW+DPL3,,>
Video_Sel       =       VideoBuf-GDT
;----------------------------------------------------------------------------
EFFGDT          LABEL   BYTE
                ;演示任务的局部描述符表段的描述符及选择子
DemoLDTab       Desc    <DemoLDTLen-1,DemoLDTSeg,,ATLDT,,>
DemoLDT_Sel     =       DemoLDTab-GDT
                ;演示任务的任务状态段描述符及选择子
DemoTSS         Desc    <DemoTSSLen-1,DemoTSSSeg,,AT386TSS,,>
DemoTSS_Sel     =       DemoTSS-GDT
                ;临时任务的任务状态段描述符及选择子
TempTSS         Desc    <TempTSSLen-1,TempTSSSeg,,AT386TSS+DPL2,,>
TempTSS_Sel     =       TempTSS-GDT
                ;临时代码段描述符及选择子
TempCode        Desc    <0ffffh,TempCodeSeg,,ATCE,,>
TempCode_Sel    =       TempCode-GDT
                ;子程序代码段描述符及选择子
SubR            Desc    <SubRLen16-1,SubRSeg,,ATCE,D32,>
                ;这句改过原版是SubR            Desc    <SubRLen-1,SubRSeg,,ATCE,D32,>

SubR_Sel        =       SubR-GDT
;----------------------------------------------------------------------------
GDNum           =       ($-EFFGDT)/(SIZE Desc)    ;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      Desc    <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      Desc    <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        Desc    <DemoCodeLen16-1,DemoCodeSeg,,ATCE+DPL2,D32,>
;以上这句改过，原版是DemoCode        Desc    <DemoCodeLen-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        Desc    <DemoDataLen16-1,DemoDataSeg,,ATDW+DPL3,D32,>
;以上这句改过，原版是DemoData        Desc    <DemoDataLen-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          Desc    <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          Desc    <TempTSSLen-1,TempTSSSeg,,ATDW+DPL2,,>
ToTTSS_Sel      =       ToTTSS-DemoLDT+TIL
;----------------------------------------------------------------------------
DemoLDNum       =       ($-DemoLDT)/(SIZE Desc)   ;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    <SubRB16,SubR_Sel,,AT386CGate+DPL3,>
;以上这句改过，原版是ToSubR          Gate    <SubRB,SubR_Sel,,AT386CGate+DPL3,>

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    <,TempTSS_Sel,,ATTaskGate+DPL3,>
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      0,0                       ;1级堆栈选择子(实例不使用)
                DD      0                         ;2级堆栈指针
                DW      0,0                       ;2级堆栈选择子
                DD      0                         ;CR3
                DW      DemoBegin16,0     ;这一句改过，原版是DW      DemoBegin,0
                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      1986                      ;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      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
DemoDataLen     =       $
DemoDataLen16  = WORD PTR DemoDataLen
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
;----------------------------------------------------------------------------
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