OSDev.org

Posted: **Thu Dec 14, 2006 10:34 am**

What can I do with int 31 in Protected Mode? I see this code in a program working in PM:

/* register data for calling real mode interrupts (DPMI format) */
typedef union 
{
   struct {
      unsigned long edi;
      unsigned long esi;
      unsigned long ebp;
      unsigned long res;
      unsigned long ebx;
      unsigned long edx;
      unsigned long ecx;
      unsigned long eax;
   } d;
   struct {
      unsigned short di, di_hi;
      unsigned short si, si_hi;
      unsigned short bp, bp_hi;
      unsigned short res, res_hi;
      unsigned short bx, bx_hi;
      unsigned short dx, dx_hi;
      unsigned short cx, cx_hi;
      unsigned short ax, ax_hi;
      unsigned short flags;
      unsigned short es;
      unsigned short ds;
      unsigned short fs;
      unsigned short gs;
      unsigned short ip;
      unsigned short cs;
      unsigned short sp;
      unsigned short ss;
   } x;
   struct {
      unsigned char edi[4];
      unsigned char esi[4];
      unsigned char ebp[4];
      unsigned char res[4];
      unsigned char bl, bh, ebx_b2, ebx_b3;
      unsigned char dl, dh, edx_b2, edx_b3;
      unsigned char cl, ch, ecx_b2, ecx_b3;
      unsigned char al, ah, eax_b2, eax_b3;
   } h;
} RM_REGS;

void rm_int(int num, RM_REGS *regs)
{
   regs->x.flags = 0;
   regs->x.sp = 0;
   regs->x.ss = 0;

   asm (
      " int $0x31 "
   :

   : "a" (0x300),
     "b" (num),
     "c" (0),
     "D" (regs)

   : "%eax", 
     "%ebx", 
     "%ecx", 
     "%edx", 
     "%esi", 
     "%edi"
   );
}

The rm_int function doesn't compile.

Posted: **Thu Dec 14, 2006 7:35 pm**

You may want to try to split your structures up a bit.
try:

Code: Select all

struct {
      unsigned long edi;
      unsigned long esi;
      unsigned long ebp;
      unsigned long res;
      unsigned long ebx;
      unsigned long edx;
      unsigned long ecx;
      unsigned long eax;
   } D;

   struct {
      unsigned short di, di_hi;
      unsigned short si, si_hi;
      unsigned short bp, bp_hi;
      unsigned short res, res_hi;
      unsigned short bx, bx_hi;
      unsigned short dx, dx_hi;
      unsigned short cx, cx_hi;
      unsigned short ax, ax_hi;
      unsigned short flags;
      unsigned short es;
      unsigned short ds;
      unsigned short fs;
      unsigned short gs;
      unsigned short ip;
      unsigned short cs;
      unsigned short sp;
      unsigned short ss;
   } X;

   struct {
      unsigned char edi[4];
      unsigned char esi[4];
      unsigned char ebp[4];
      unsigned char res[4];
      unsigned char bl, bh, ebx_b2, ebx_b3;
      unsigned char dl, dh, edx_b2, edx_b3;
      unsigned char cl, ch, ecx_b2, ecx_b3;
      unsigned char al, ah, eax_b2, eax_b3;
   } H;

typedef union
{
   struct D d;
   struct X x;
   struct H h;
} RM_REGS;

and make sure you have

Code: Select all

#define asm __asm__ __volatile__

But quickly reading over the code and without knowing what error the compiler is giving you, I don't know your problem for sure.

Posted: **Fri Dec 15, 2006 9:01 am**

the error is on this line:

Code: Select all

   asm ( 
      " int $0x31 " 
   : 

   : "a" (0x300), 
     "b" (num), 
     "c" (0), 
     "D" (regs) 

   : "%eax", 
     "%ebx", 
     "%ecx", 
     "%edx", 
     "%esi", 
     "%edi" 
   );

Now I can't give you the error that the compiler give me

Posted: **Sun Dec 17, 2006 7:48 am**

INT 31 is used to acces DPMI(Dos protected mode interface). It is used under DOS and Win9x by apps to get to protected mode and then to make operations like changing memory selectors etc and also calling RM interrupts. But it's a Dossish thing, so hands away.

Posted: **Mon Dec 18, 2006 5:46 am**

ntfs wrote:INT 31 is used to acces DPMI(Dos protected mode interface). It is used under DOS and Win9x by apps to get to protected mode and then to make operations like changing memory selectors etc and also calling RM interrupts. But it's a Dossish thing, so hands away.

ok thank you!

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