请问DOS下怎样访问32位的地址空间? - DOS开发编程 & 发展交流（开发室） - 中国DOS联盟论坛

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1:use watcom in 32bit
char *buf=(char*)0xd800000;
i=*buf

2:use dos
typedef struct
{ char gdt0;
char gdt1;
unsigned int srclimit;
unsigned int srclw;
unsigned char srclb;
unsigned char srcrights;
unsigned char srcflag;
unsigned char srchb;
unsigned int trglimit;
unsigned int trglw;
unsigned char trglb;
unsigned char trgrights;
unsigned char trgflag;
unsigned char trghb;
char bioscs;
char biosss;
}gdt;
gdt For2_gdt;

int For2_read(unsigned long srcaddress,char far *bufer,unsigned int lenth)
{ unsigned int i,j;
unsigned char cc,ccl,cch;
char far *fp1;

int15init();
fp1=&bufer;
i=FP_SEG(fp1);
j=FP_OFF(fp1);
_asm{
mov ax,i
mov dx,ax
mov bx,j
mov cl,04h
shl dx,cl
rol ax,cl
and ax,0fh
add bx,dx
adc al,0
mov i,bx
mov cc,al
}
For2_gdt.trglimit=0xffff;
For2_gdt.trglw=i;
For2_gdt.trglb=cc;
For2_gdt.trghb=0;
For2_gdt.trgflag=0x4;
For2_gdt.srclimit=0xffff;
For2_gdt.srclw=(unsigned int)(srcaddress&0xffff);
For2_gdt.srclb=(unsigned char)((srcaddress>>16)&0xff);
For2_gdt.srchb=(unsigned char)((srcaddress>>24)&0xff);
For2_gdt.srcflag=0x4;
For2_gdt.srcrights=0x92;
For2_gdt.trgrights=0x92;
fp1=&(For2_gdt.gdt0);
i=FP_SEG(fp1);
j=FP_OFF(fp1);
_asm{
mov ax,i
mov es,ax
mov si,j
mov cx,lenth
mov ah,87h
int 15h
mov i,ax
}
return i;
}
void int15init()
{ int i;

for(i=0;i<8;i++)
{ // For2_gdt.bioscs=0;
// For2_gdt.biosss=0;
For2_gdt.gdt0=0;
For2_gdt.gdt1=0;
}
For2_gdt.bioscs=0xff;
For2_gdt.bioscs=0xff;
For2_gdt.bioscs=0;
For2_gdt.bioscs=0;
For2_gdt.bioscs=0x0f;
For2_gdt.bioscs=0x9b;
For2_gdt.bioscs=0;
For2_gdt.bioscs=0;
For2_gdt.biosss=0xff;
For2_gdt.biosss=0xff;
For2_gdt.biosss=0;
For2_gdt.biosss=3;
For2_gdt.biosss=0;
For2_gdt.biosss=0x93;
For2_gdt.biosss=0;
For2_gdt.biosss=0;
}