mirror of https://github.com/acidanthera/audk.git
281 lines
11 KiB
C
281 lines
11 KiB
C
/** @file
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Real Mode Thunk Functions for IA32 and x64.
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Copyright (c) 2006 - 2008, Intel Corporation<BR>
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All rights reserved. This program and the accompanying materials
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are licensed and made available under the terms and conditions of the BSD License
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which accompanies this distribution. The full text of the license may be found at
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http://opensource.org/licenses/bsd-license.php
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THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
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WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
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**/
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#include "BaseLibInternals.h"
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//
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// Byte packed structure for a segment descriptor in a GDT/LDT
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//
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typedef union {
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struct {
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UINT32 LimitLow:16;
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UINT32 BaseLow:16;
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UINT32 BaseMid:8;
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UINT32 Type:4;
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UINT32 S:1;
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UINT32 DPL:2;
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UINT32 P:1;
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UINT32 LimitHigh:4;
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UINT32 AVL:1;
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UINT32 L:1;
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UINT32 DB:1;
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UINT32 G:1;
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UINT32 BaseHigh:8;
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} Bits;
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UINT64 Uint64;
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} IA32_SEGMENT_DESCRIPTOR;
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extern CONST UINT8 m16Start;
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extern CONST UINT16 m16Size;
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extern CONST UINT16 mThunk16Attr;
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extern CONST UINT16 m16Gdt;
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extern CONST UINT16 m16GdtrBase;
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extern CONST UINT16 mTransition;
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/**
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Invokes 16-bit code in big real mode and returns the updated register set.
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This function transfers control to the 16-bit code specified by CS:EIP using
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the stack specified by SS:ESP in RegisterSet. The updated registers are saved
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on the real mode stack and the starting address of the save area is returned.
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@param RegisterSet Values of registers before invocation of 16-bit code.
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@param Transition Pointer to the transition code under 1MB.
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@return The pointer to a IA32_REGISTER_SET structure containing the updated
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register values.
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**/
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IA32_REGISTER_SET *
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EFIAPI
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InternalAsmThunk16 (
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IN IA32_REGISTER_SET *RegisterSet,
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IN OUT VOID *Transition
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);
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/**
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Retrieves the properties for 16-bit thunk functions.
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Computes the size of the buffer and stack below 1MB required to use the
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AsmPrepareThunk16(), AsmThunk16() and AsmPrepareAndThunk16() functions. This
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buffer size is returned in RealModeBufferSize, and the stack size is returned
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in ExtraStackSize. If parameters are passed to the 16-bit real mode code,
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then the actual minimum stack size is ExtraStackSize plus the maximum number
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of bytes that need to be passed to the 16-bit real mode code.
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If RealModeBufferSize is NULL, then ASSERT().
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If ExtraStackSize is NULL, then ASSERT().
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@param RealModeBufferSize A pointer to the size of the buffer below 1MB
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required to use the 16-bit thunk functions.
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@param ExtraStackSize A pointer to the extra size of stack below 1MB
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that the 16-bit thunk functions require for
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temporary storage in the transition to and from
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16-bit real mode.
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**/
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VOID
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EFIAPI
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AsmGetThunk16Properties (
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OUT UINT32 *RealModeBufferSize,
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OUT UINT32 *ExtraStackSize
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)
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{
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ASSERT (RealModeBufferSize != NULL);
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ASSERT (ExtraStackSize != NULL);
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*RealModeBufferSize = m16Size;
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//
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// Extra 4 bytes for return address, and another 4 bytes for mode transition
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//
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*ExtraStackSize = sizeof (IA32_DWORD_REGS) + 8;
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}
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/**
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Prepares all structures a code required to use AsmThunk16().
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Prepares all structures and code required to use AsmThunk16().
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If ThunkContext is NULL, then ASSERT().
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@param ThunkContext A pointer to the context structure that describes the
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16-bit real mode code to call.
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**/
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VOID
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EFIAPI
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AsmPrepareThunk16 (
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OUT THUNK_CONTEXT *ThunkContext
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)
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{
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IA32_SEGMENT_DESCRIPTOR *RealModeGdt;
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ASSERT (ThunkContext != NULL);
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ASSERT ((UINTN)ThunkContext->RealModeBuffer < 0x100000);
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ASSERT (ThunkContext->RealModeBufferSize >= m16Size);
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ASSERT ((UINTN)ThunkContext->RealModeBuffer + m16Size <= 0x100000);
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CopyMem (ThunkContext->RealModeBuffer, &m16Start, m16Size);
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//
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// Point RealModeGdt to the GDT to be used in transition
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//
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// RealModeGdt[0]: Reserved as NULL descriptor
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// RealModeGdt[1]: Code Segment
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// RealModeGdt[2]: Data Segment
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// RealModeGdt[3]: Call Gate
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//
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RealModeGdt = (IA32_SEGMENT_DESCRIPTOR*)(
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(UINTN)ThunkContext->RealModeBuffer + m16Gdt);
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//
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// Update Code & Data Segment Descriptor
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//
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RealModeGdt[1].Bits.BaseLow =
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(UINT32)(UINTN)ThunkContext->RealModeBuffer & ~0xf;
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RealModeGdt[1].Bits.BaseMid =
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(UINT32)(UINTN)ThunkContext->RealModeBuffer >> 16;
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//
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// Update transition code entry point offset
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//
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*(UINT32*)((UINTN)ThunkContext->RealModeBuffer + mTransition) +=
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(UINT32)(UINTN)ThunkContext->RealModeBuffer & 0xf;
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//
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// Update Segment Limits for both Code and Data Segment Descriptors
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//
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if ((ThunkContext->ThunkAttributes & THUNK_ATTRIBUTE_BIG_REAL_MODE) == 0) {
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//
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// Set segment limits to 64KB
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//
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RealModeGdt[1].Bits.LimitHigh = 0;
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RealModeGdt[1].Bits.G = 0;
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RealModeGdt[2].Bits.LimitHigh = 0;
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RealModeGdt[2].Bits.G = 0;
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}
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//
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// Update GDTBASE for this thunk context
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//
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*(VOID**)((UINTN)ThunkContext->RealModeBuffer + m16GdtrBase) = RealModeGdt;
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//
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// Update Thunk Attributes
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//
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*(UINT32*)((UINTN)ThunkContext->RealModeBuffer + mThunk16Attr) =
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ThunkContext->ThunkAttributes;
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}
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/**
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Transfers control to a 16-bit real mode entry point and returns the results.
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Transfers control to a 16-bit real mode entry point and returns the results.
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AsmPrepareThunk16() must be called with ThunkContext before this function is used.
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This function must be called with interrupts disabled.
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The register state from the RealModeState field of ThunkContext is restored just prior
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to calling the 16-bit real mode entry point. This includes the EFLAGS field of RealModeState,
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which is used to set the interrupt state when a 16-bit real mode entry point is called.
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Control is transferred to the 16-bit real mode entry point specified by the CS and Eip fields of RealModeState.
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The stack is initialized to the SS and ESP fields of RealModeState. Any parameters passed to
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the 16-bit real mode code must be populated by the caller at SS:ESP prior to calling this function.
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The 16-bit real mode entry point is invoked with a 16-bit CALL FAR instruction,
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so when accessing stack contents, the 16-bit real mode code must account for the 16-bit segment
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and 16-bit offset of the return address that were pushed onto the stack. The 16-bit real mode entry
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point must exit with a RETF instruction. The register state is captured into RealModeState immediately
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after the RETF instruction is executed.
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If EFLAGS specifies interrupts enabled, or any of the 16-bit real mode code enables interrupts,
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or any of the 16-bit real mode code makes a SW interrupt, then the caller is responsible for making sure
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the IDT at address 0 is initialized to handle any HW or SW interrupts that may occur while in 16-bit real mode.
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If EFLAGS specifies interrupts enabled, or any of the 16-bit real mode code enables interrupts,
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then the caller is responsible for making sure the 8259 PIC is in a state compatible with 16-bit real mode.
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This includes the base vectors, the interrupt masks, and the edge/level trigger mode.
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If THUNK_ATTRIBUTE_BIG_REAL_MODE is set in the ThunkAttributes field of ThunkContext, then the user code
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is invoked in big real mode. Otherwise, the user code is invoked in 16-bit real mode with 64KB segment limits.
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If neither THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 nor THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL are set in
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ThunkAttributes, then it is assumed that the user code did not enable the A20 mask, and no attempt is made to
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disable the A20 mask.
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If THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 is set and THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL is clear in
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ThunkAttributes, then attempt to use the INT 15 service to disable the A20 mask. If this INT 15 call fails,
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then attempt to disable the A20 mask by directly accessing the 8042 keyboard controller I/O ports.
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If THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 is clear and THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL is set in
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ThunkAttributes, then attempt to disable the A20 mask by directly accessing the 8042 keyboard controller I/O ports.
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If ThunkContext is NULL, then ASSERT().
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If AsmPrepareThunk16() was not previously called with ThunkContext, then ASSERT().
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If both THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 and THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL are set in
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ThunkAttributes, then ASSERT().
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@param ThunkContext A pointer to the context structure that describes the
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16-bit real mode code to call.
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**/
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VOID
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EFIAPI
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AsmThunk16 (
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IN OUT THUNK_CONTEXT *ThunkContext
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)
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{
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IA32_REGISTER_SET *UpdatedRegs;
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ASSERT (ThunkContext != NULL);
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ASSERT ((UINTN)ThunkContext->RealModeBuffer < 0x100000);
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ASSERT (ThunkContext->RealModeBufferSize >= m16Size);
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ASSERT ((UINTN)ThunkContext->RealModeBuffer + m16Size <= 0x100000);
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UpdatedRegs = InternalAsmThunk16 (
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ThunkContext->RealModeState,
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ThunkContext->RealModeBuffer
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);
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CopyMem (ThunkContext->RealModeState, UpdatedRegs, sizeof (*UpdatedRegs));
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}
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/**
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Prepares all structures and code for a 16-bit real mode thunk, transfers
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control to a 16-bit real mode entry point, and returns the results.
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Prepares all structures and code for a 16-bit real mode thunk, transfers
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control to a 16-bit real mode entry point, and returns the results. If the
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caller only need to perform a single 16-bit real mode thunk, then this
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service should be used. If the caller intends to make more than one 16-bit
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real mode thunk, then it is more efficient if AsmPrepareThunk16() is called
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once and AsmThunk16() can be called for each 16-bit real mode thunk.
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See AsmPrepareThunk16() and AsmThunk16() for the detailed description and ASSERT() conditions.
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@param ThunkContext A pointer to the context structure that describes the
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16-bit real mode code to call.
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**/
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VOID
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EFIAPI
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AsmPrepareAndThunk16 (
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IN OUT THUNK_CONTEXT *ThunkContext
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)
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{
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AsmPrepareThunk16 (ThunkContext);
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AsmThunk16 (ThunkContext);
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}
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