X86Thunk.c

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#include "BaseLibInternals.h"
 
extern CONST UINT8   m16Start;
extern CONST UINT16  m16Size;
extern CONST UINT16  mThunk16Attr;
extern CONST UINT16  m16Gdt;
extern CONST UINT16  m16GdtrBase;
extern CONST UINT16  mTransition;
 
IA32_REGISTER_SET *
EFIAPI
InternalAsmThunk16 (
  IN      IA32_REGISTER_SET  *RegisterSet,
  IN OUT  VOID               *Transition
  );
 
VOID
EFIAPI
AsmGetThunk16Properties (
  OUT     UINT32  *RealModeBufferSize,
  OUT     UINT32  *ExtraStackSize
  )
{
  ASSERT (RealModeBufferSize != NULL);
  ASSERT (ExtraStackSize != NULL);
 
  *RealModeBufferSize = m16Size;
 
  //
  // Extra 4 bytes for return address, and another 4 bytes for mode transition
  //
  *ExtraStackSize = sizeof (IA32_DWORD_REGS) + 8;
}
 
VOID
EFIAPI
AsmPrepareThunk16 (
  IN OUT  THUNK_CONTEXT  *ThunkContext
  )
{
  IA32_SEGMENT_DESCRIPTOR  *RealModeGdt;
 
  ASSERT (ThunkContext != NULL);
  ASSERT ((UINTN)ThunkContext->RealModeBuffer < 0x100000);
  ASSERT (ThunkContext->RealModeBufferSize >= m16Size);
  ASSERT ((UINTN)ThunkContext->RealModeBuffer + m16Size <= 0x100000);
 
  CopyMem (ThunkContext->RealModeBuffer, &m16Start, m16Size);
 
  //
  // Point RealModeGdt to the GDT to be used in transition
  //
  // RealModeGdt[0]: Reserved as NULL descriptor
  // RealModeGdt[1]: Code Segment
  // RealModeGdt[2]: Data Segment
  // RealModeGdt[3]: Call Gate
  //
  RealModeGdt = (IA32_SEGMENT_DESCRIPTOR *)(
                                            (UINTN)ThunkContext->RealModeBuffer + m16Gdt);
 
  //
  // Update Code & Data Segment Descriptor
  //
  RealModeGdt[1].Bits.BaseLow =
    (UINT32)(UINTN)ThunkContext->RealModeBuffer & ~0xf;
  RealModeGdt[1].Bits.BaseMid =
    (UINT32)(UINTN)ThunkContext->RealModeBuffer >> 16;
 
  //
  // Update transition code entry point offset
  //
  *(UINT32 *)((UINTN)ThunkContext->RealModeBuffer + mTransition) +=
    (UINT32)(UINTN)ThunkContext->RealModeBuffer & 0xf;
 
  //
  // Update Segment Limits for both Code and Data Segment Descriptors
  //
  if ((ThunkContext->ThunkAttributes & THUNK_ATTRIBUTE_BIG_REAL_MODE) == 0) {
    //
    // Set segment limits to 64KB
    //
    RealModeGdt[1].Bits.LimitHigh = 0;
    RealModeGdt[1].Bits.G         = 0;
    RealModeGdt[2].Bits.LimitHigh = 0;
    RealModeGdt[2].Bits.G         = 0;
  }
 
  //
  // Update GDTBASE for this thunk context
  //
  *(VOID **)((UINTN)ThunkContext->RealModeBuffer + m16GdtrBase) = RealModeGdt;
 
  //
  // Update Thunk Attributes
  //
  *(UINT32 *)((UINTN)ThunkContext->RealModeBuffer + mThunk16Attr) =
    ThunkContext->ThunkAttributes;
}
 
VOID
EFIAPI
AsmThunk16 (
  IN OUT  THUNK_CONTEXT  *ThunkContext
  )
{
  IA32_REGISTER_SET  *UpdatedRegs;
 
  ASSERT (ThunkContext != NULL);
  ASSERT ((UINTN)ThunkContext->RealModeBuffer < 0x100000);
  ASSERT (ThunkContext->RealModeBufferSize >= m16Size);
  ASSERT ((UINTN)ThunkContext->RealModeBuffer + m16Size <= 0x100000);
  ASSERT (
    ((ThunkContext->ThunkAttributes & (THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 | THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL)) != \
     (THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 | THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL))
    );
 
  UpdatedRegs = InternalAsmThunk16 (
                  ThunkContext->RealModeState,
                  ThunkContext->RealModeBuffer
                  );
 
  CopyMem (ThunkContext->RealModeState, UpdatedRegs, sizeof (*UpdatedRegs));
}
 
VOID
EFIAPI
AsmPrepareAndThunk16 (
  IN OUT  THUNK_CONTEXT  *ThunkContext
  )
{
  AsmPrepareThunk16 (ThunkContext);
  AsmThunk16 (ThunkContext);
}