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/** @file
Real Mode Thunk Functions for IA32 and X64.
Copyright (c) 2006, Intel Corporation<BR>
All rights reserved. This program and the accompanying materials
are licensed and made available under the terms and conditions of the BSD License
which accompanies this distribution. The full text of the license may be found at
http://opensource.org/licenses/bsd-license.php
THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
**/
#include <BaseLibInternals.h>
//
// Byte packed structure for a segment descriptor in a GDT/LDT
//
typedef union {
struct {
UINT32 LimitLow:16;
UINT32 BaseLow:16;
UINT32 BaseMid:8;
UINT32 Type:4;
UINT32 S:1;
UINT32 DPL:2;
UINT32 P:1;
UINT32 LimitHigh:4;
UINT32 AVL:1;
UINT32 L:1;
UINT32 DB:1;
UINT32 G:1;
UINT32 BaseHigh:8;
} Bits;
UINT64 Uint64;
} IA32_SEGMENT_DESCRIPTOR;
extern CONST UINT8 m16Start;
extern CONST UINT16 m16Size;
extern CONST UINT16 mThunk16Attr;
extern CONST UINT16 m16Gdt;
extern CONST UINT16 m16GdtrBase;
extern CONST UINT16 mTransition;
/**
Invokes 16-bit code in big real mode and returns the updated register set.
This function transfers control to the 16-bit code specified by CS:EIP using
the stack specified by SS:ESP in RegisterSet. The updated registers are saved
on the real mode stack and the starting address of the save area is returned.
@param RegisterSet Values of registers before invocation of 16-bit code.
@param Transition Pointer to the transition code under 1MB.
@return The pointer to a IA32_REGISTER_SET structure containing the updated
register values.
**/
IA32_REGISTER_SET *
EFIAPI
InternalAsmThunk16 (
IN IA32_REGISTER_SET *RegisterSet,
IN OUT VOID *Transition
);
/**
Retrieves the properties for 16-bit thunk functions.
Computes the size of the buffer and stack below 1MB required to use the
AsmPrepareThunk16(), AsmThunk16() and AsmPrepareAndThunk16() functions. This
buffer size is returned in RealModeBufferSize, and the stack size is returned
in ExtraStackSize. If parameters are passed to the 16-bit real mode code,
then the actual minimum stack size is ExtraStackSize plus the maximum number
of bytes that need to be passed to the 16-bit real mode code.
If RealModeBufferSize is NULL, then ASSERT().
If ExtraStackSize is NULL, then ASSERT().
@param RealModeBufferSize A pointer to the size of the buffer below 1MB
required to use the 16-bit thunk functions.
@param ExtraStackSize A pointer to the extra size of stack below 1MB
that the 16-bit thunk functions require for
temporary storage in the transition to and from
16-bit real mode.
**/
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;
}
/**
Prepares all structures a code required to use AsmThunk16().
Prepares all structures and code required to use AsmThunk16().
If ThunkContext is NULL, then ASSERT().
@param ThunkContext A pointer to the context structure that describes the
16-bit real mode code to call.
**/
VOID
EFIAPI
AsmPrepareThunk16 (
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;
}
/**
Transfers control to a 16-bit real mode entry point and returns the results.
Transfers control to a 16-bit real mode entry point and returns the results.
AsmPrepareThunk16() must be called with ThunkContext before this function is
used. This function must be called with interrupts disabled.
If ThunkContext is NULL, then ASSERT().
If AsmPrepareThunk16() was not previously called with ThunkContext, then ASSERT().
@param ThunkContext A pointer to the context structure that describes the
16-bit real mode code to call.
**/
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);
UpdatedRegs = InternalAsmThunk16 (
ThunkContext->RealModeState,
ThunkContext->RealModeBuffer
);
CopyMem (ThunkContext->RealModeState, UpdatedRegs, sizeof (*UpdatedRegs));
}
/**
Prepares all structures and code for a 16-bit real mode thunk, transfers
control to a 16-bit real mode entry point, and returns the results.
Prepares all structures and code for a 16-bit real mode thunk, transfers
control to a 16-bit real mode entry point, and returns the results. If the
caller only need to perform a single 16-bit real mode thunk, then this
service should be used. If the caller intends to make more than one 16-bit
real mode thunk, then it is more efficient if AsmPrepareThunk16() is called
once and AsmThunk16() can be called for each 16-bit real mode thunk. This
function must be called with interrupts disabled.
If ThunkContext is NULL, then ASSERT().
@param ThunkContext A pointer to the context structure that describes the
16-bit real mode code to call.
**/
VOID
EFIAPI
AsmPrepareAndThunk16 (
IN OUT THUNK_CONTEXT *ThunkContext
)
{
AsmPrepareThunk16 (ThunkContext);
AsmThunk16 (ThunkContext);
}
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