2 Real Mode Thunk Functions for IA32 and X64.
4 Copyright (c) 2006, Intel Corporation<BR>
5 All rights reserved. This program and the accompanying materials
6 are licensed and made available under the terms and conditions of the BSD License
7 which accompanies this distribution. The full text of the license may be found at
8 http://opensource.org/licenses/bsd-license.php
10 THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
11 WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
13 Module Name: x86Thunk.c
18 // Byte packed structure for a segment descriptor in a GDT/LDT
37 } IA32_SEGMENT_DESCRIPTOR
;
39 extern CONST UINT8 m16Start
;
40 extern CONST UINT16 m16Size
;
41 extern CONST UINT16 mThunk16Attr
;
42 extern CONST UINT16 m16Gdt
;
43 extern CONST UINT16 m16GdtrBase
;
44 extern CONST UINT16 mTransition
;
47 Invokes 16-bit code in big real mode and returns the updated register set.
49 This function transfers control to the 16-bit code specified by CS:EIP using
50 the stack specified by SS:ESP in RegisterSet. The updated registers are saved
51 on the real mode stack and the starting address of the save area is returned.
53 @param RegisterSet Values of registers before invocation of 16-bit code.
54 @param Transition Pointer to the transition code under 1MB.
56 @return The pointer to a IA32_REGISTER_SET structure containing the updated
62 IN IA32_REGISTER_SET
*RegisterSet
,
63 IN OUT VOID
*Transition
67 Retrieves the properties for 16-bit thunk functions.
69 Computes the size of the buffer and stack below 1MB required to use the
70 AsmPrepareThunk16(), AsmThunk16() and AsmPrepareAndThunk16() functions. This
71 buffer size is returned in RealModeBufferSize, and the stack size is returned
72 in ExtraStackSize. If parameters are passed to the 16-bit real mode code,
73 then the actual minimum stack size is ExtraStackSize plus the maximum number
74 of bytes that need to be passed to the 16-bit real mode code.
76 If RealModeBufferSize is NULL, then ASSERT().
77 If ExtraStackSize is NULL, then ASSERT().
79 @param RealModeBufferSize A pointer to the size of the buffer below 1MB
80 required to use the 16-bit thunk functions.
81 @param ExtraStackSize A pointer to the extra size of stack below 1MB
82 that the 16-bit thunk functions require for
83 temporary storage in the transition to and from
89 AsmGetThunk16Properties (
90 OUT UINT32
*RealModeBufferSize
,
91 OUT UINT32
*ExtraStackSize
94 ASSERT (RealModeBufferSize
!= NULL
);
95 ASSERT (ExtraStackSize
!= NULL
);
97 *RealModeBufferSize
= m16Size
;
98 *ExtraStackSize
= sizeof (IA32_DWORD_REGS
) + 8;
102 Prepares all structures a code required to use AsmThunk16().
104 Prepares all structures and code required to use AsmThunk16().
106 If ThunkContext is NULL, then ASSERT().
108 @param ThunkContext A pointer to the context structure that describes the
109 16-bit real mode code to call.
115 OUT THUNK_CONTEXT
*ThunkContext
118 IA32_SEGMENT_DESCRIPTOR
*RealModeGdt
;
120 ASSERT (ThunkContext
!= NULL
);
121 ASSERT ((UINTN
)ThunkContext
->RealModeBuffer
< 0x100000);
122 ASSERT (ThunkContext
->RealModeBufferSize
>= m16Size
);
123 ASSERT ((UINTN
)ThunkContext
->RealModeBuffer
+ m16Size
<= 0x100000);
124 ASSERT (((UINTN
)ThunkContext
->RealModeBuffer
& 0x0f) == 0);
126 CopyMem (ThunkContext
->RealModeBuffer
, &m16Start
, m16Size
);
129 // Point RealModeGdt to the GDT to be used in transition
131 // RealModeGdt[0]: Reserved as NULL descriptor
132 // RealModeGdt[1]: Code Segment
133 // RealModeGdt[2]: Data Segment
134 // RealModeGdt[3]: Call Gate
136 RealModeGdt
= (IA32_SEGMENT_DESCRIPTOR
*)(
137 (UINTN
)ThunkContext
->RealModeBuffer
+ m16Gdt
);
140 // Update Code & Data Segment Descriptor
142 RealModeGdt
[1].Bits
.BaseLow
=
143 (UINT32
)(UINTN
)ThunkContext
->RealModeBuffer
& ~0xf;
144 RealModeGdt
[1].Bits
.BaseMid
=
145 (UINT32
)(UINTN
)ThunkContext
->RealModeBuffer
>> 16;
148 // Update transition code entry point offset
150 *(UINT32
*)((UINTN
)ThunkContext
->RealModeBuffer
+ mTransition
) +=
151 (UINT32
)(UINTN
)ThunkContext
->RealModeBuffer
& 0xf;
154 // Update Segment Limits for both Code and Data Segment Descriptors
156 if ((ThunkContext
->ThunkAttributes
& THUNK_ATTRIBUTE_BIG_REAL_MODE
) == 0) {
158 // Set segment limits to 64KB
160 RealModeGdt
[1].Bits
.LimitHigh
= 0;
161 RealModeGdt
[1].Bits
.G
= 0;
162 RealModeGdt
[2].Bits
.LimitHigh
= 0;
163 RealModeGdt
[2].Bits
.G
= 0;
167 // Update GDTBASE for this thunk context
169 *(VOID
**)((UINTN
)ThunkContext
->RealModeBuffer
+ m16GdtrBase
) = RealModeGdt
;
172 // Update Thunk Attributes
174 *(UINT32
*)((UINTN
)ThunkContext
->RealModeBuffer
+ mThunk16Attr
) =
175 ThunkContext
->ThunkAttributes
;
179 Transfers control to a 16-bit real mode entry point and returns the results.
181 Transfers control to a 16-bit real mode entry point and returns the results.
182 AsmPrepareThunk16() must be called with ThunkContext before this function is
183 used. This function must be called with interrupts disabled.
185 If ThunkContext is NULL, then ASSERT().
186 If AsmPrepareThunk16() was not previously called with ThunkContext, then ASSERT().
188 @param ThunkContext A pointer to the context structure that describes the
189 16-bit real mode code to call.
195 IN OUT THUNK_CONTEXT
*ThunkContext
198 IA32_REGISTER_SET
*UpdatedRegs
;
200 ASSERT (ThunkContext
!= NULL
);
201 ASSERT ((UINTN
)ThunkContext
->RealModeBuffer
< 0x100000);
202 ASSERT (ThunkContext
->RealModeBufferSize
>= m16Size
);
203 ASSERT ((UINTN
)ThunkContext
->RealModeBuffer
+ m16Size
<= 0x100000);
204 ASSERT (((UINTN
)ThunkContext
->RealModeBuffer
& 0x0f) == 0);
206 UpdatedRegs
= InternalAsmThunk16 (
207 ThunkContext
->RealModeState
,
208 ThunkContext
->RealModeBuffer
211 CopyMem (ThunkContext
->RealModeState
, UpdatedRegs
, sizeof (*UpdatedRegs
));
215 Prepares all structures and code for a 16-bit real mode thunk, transfers
216 control to a 16-bit real mode entry point, and returns the results.
218 Prepares all structures and code for a 16-bit real mode thunk, transfers
219 control to a 16-bit real mode entry point, and returns the results. If the
220 caller only need to perform a single 16-bit real mode thunk, then this
221 service should be used. If the caller intends to make more than one 16-bit
222 real mode thunk, then it is more efficient if AsmPrepareThunk16() is called
223 once and AsmThunk16() can be called for each 16-bit real mode thunk. This
224 function must be called with interrupts disabled.
226 If ThunkContext is NULL, then ASSERT().
228 @param ThunkContext A pointer to the context structure that describes the
229 16-bit real mode code to call.
234 AsmPrepareAndThunk16 (
235 IN OUT THUNK_CONTEXT
*ThunkContext
238 AsmPrepareThunk16 (ThunkContext
);
239 AsmThunk16 (ThunkContext
);