pmtest8.asm中对PagingDemo程序段的理解

; 测试分页机制 --------------------------------------------------------------
PagingDemo:
  mov ax, cs
 mov ds, ax
 mov ax, SelectorFlatRW       ;这应该是selectorFlatRW所对应的段描述符的首地址，参见pmtest7.asm
 mov es, ax

 push LenFoo          ;0x0000001c                 sp:0x000001f7
 push OffsetFoo       ;0x000001a0                 sp:0x000001f3
 push ProcFoo         ;ProcFoo equ 00401000h   sp:0x000001ef
 call MemCpy          ;前面几个push是MemCpy的参数,sp:0x000001eb,call会由系统自动压入参数，sp要加4。这段call的功能是把程序拷贝到ProcFoo处
 add esp, 12             ;esp:0x000001fb,见lib.inc ,168行.

 push LenBar          ;0x0000001e                 sp:0x000001f7
 push OffsetBar       ;0x000001bc
 push ProcBar         ;0x00501000
 call MemCpy          ;这段call的功能是把程序拷贝到ProcBar处
 add esp, 12

 push LenPagingDemoAll        ;0x00000008
 push OffsetPagingDemoProc    ;0x00000198
 push ProcPagingDemo          ;0x00301000
 call MemCpy                  ;这段call的功能是把程序拷贝到ProcPagingDemo处
 add esp, 12

 mov ax, SelectorData           ;0x0030
 mov ds, ax   ; 数据段选择子
 mov es, ax

 call SetupPaging  ; 启动分页
   
 call SelectorFlatC:ProcPagingDemo  ； ; call far 0010:00301000

                                                       ；跳到PagingDemoProc处，

                                                       ；执行mov eax, LinearAddrDemo   ;LinearAddrDemo equ 00401000h    ,ProcFoo equ 00401000h
                                                       ；call eax   ，执行foo函数

 call PSwitch   ; 切换页目录，改变地址映射关系

 call SelectorFlatC:ProcPagingDemo        ; call far 0010:00301000

                                                         ；跳到PagingDemoProc处，

                                                         ；执行mov eax, LinearAddrDemo   ;LinearAddrDemo equ 00401000h    ,ProcFoo equ 00401000h
                                                         ；call eax     ，执行bar函数

 ret        

补充：selectorRW和SelectorFlatC所指向都是同一个段，段基地址0，段界限为4G，只是属性不一样。其实段基址0不起作用，起作用的还是偏移量，偏移量就代表了地址。Call MemCpy需要数据的读写，所以用SelectorRW，Call SelectorFlatC:ProcPagingDemo是代码的执行，所以用SelctorFlatC。