claymation / osxp

EFI boot loader for running Windows XP on Intel Macs, from the 2006 Windows On Mac hacker challenge

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osxp / thunk.c
100644 73 lines (63 sloc) 1.408 kb
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/* EFI library includes */
#include <EfiBind.h>
#include <EfiTypes.h>
#include <EfiCommon.h>
#include <EfiApi.h>
#include <EfiDriverLib.h>
#include <EfiDevicePath.h>
 
#include "OSXP.h"
#include "thunk.h"
 
/* A stack for real mode code to use. */
UINT16 RealStack[2048];
 
SegmentDescriptor RealGDT[] = {
  { // Selector 0x00 - NULL
    0,  // LimitLow
    0,  // BaseLow
    0,  // BaseMid
    0,  // Attribute
    0,  // LimitHi
    0   // BaseHi
  },
  { // Selector 0x08 - NULL
    0,  // LimitLow
    0,  // BaseLow
    0,  // BaseMid
    0,  // Attribute
    0,  // LimitHi
    0   // BaseHi
  },
  { // Selector 0x10 - Real Code 
    0xffff,  // LimitLow
    0x0000,  // BaseLow
    0x00,    // BaseMid
    0x9a,    // Attribute
    0x0f,    // LimitHi
    0x00     // BaseHi
  },
  { // Selector 0x18 - Real Data
    0xffff,  // LimitLow
    0x0000,  // BaseLow
    0x00,    // BaseMid
    0x92,    // Attribute
    0x8f,    // LimitHi
    0x00     // BaseHi
  }
};
 
SystemTableRegister 	ProtectedIDTR;
SystemTableRegister 	ProtectedGDTR;
UINT32     		ProtectedESP;
 
SystemTableRegister RealIDTR = {
    0x3FFF,  // Limit
    0x0      // Base
};
 
SystemTableRegister RealGDTR = {
    sizeof(RealGDT) - 1,  // Limit
    (UINT32) &RealGDT     // Base
};
 
EFI_TPL ProtectedTPL;
 
void ThunkMBR()
{
    ProtectedTPL = gBS->RaiseTPL(EFI_TPL_HIGH_LEVEL);
    asmThunk();
    gBS->RestoreTPL(ProtectedTPL);
}