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.
16 #include <BaseLibInternals.h>
20 // Byte packed structure for a segment descriptor in a GDT/LDT
39 } IA32_SEGMENT_DESCRIPTOR
;
41 extern CONST UINT8 m16Start
;
42 extern CONST UINT16 m16Size
;
43 extern CONST UINT16 mThunk16Attr
;
44 extern CONST UINT16 m16Gdt
;
45 extern CONST UINT16 m16GdtrBase
;
46 extern CONST UINT16 mTransition
;
49 Invokes 16-bit code in big real mode and returns the updated register set.
51 This function transfers control to the 16-bit code specified by CS:EIP using
52 the stack specified by SS:ESP in RegisterSet. The updated registers are saved
53 on the real mode stack and the starting address of the save area is returned.
55 @param RegisterSet Values of registers before invocation of 16-bit code.
56 @param Transition Pointer to the transition code under 1MB.
58 @return The pointer to a IA32_REGISTER_SET structure containing the updated
65 IN IA32_REGISTER_SET
*RegisterSet
,
66 IN OUT VOID
*Transition
70 Retrieves the properties for 16-bit thunk functions.
72 Computes the size of the buffer and stack below 1MB required to use the
73 AsmPrepareThunk16(), AsmThunk16() and AsmPrepareAndThunk16() functions. This
74 buffer size is returned in RealModeBufferSize, and the stack size is returned
75 in ExtraStackSize. If parameters are passed to the 16-bit real mode code,
76 then the actual minimum stack size is ExtraStackSize plus the maximum number
77 of bytes that need to be passed to the 16-bit real mode code.
79 If RealModeBufferSize is NULL, then ASSERT().
80 If ExtraStackSize is NULL, then ASSERT().
82 @param RealModeBufferSize A pointer to the size of the buffer below 1MB
83 required to use the 16-bit thunk functions.
84 @param ExtraStackSize A pointer to the extra size of stack below 1MB
85 that the 16-bit thunk functions require for
86 temporary storage in the transition to and from
92 AsmGetThunk16Properties (
93 OUT UINT32
*RealModeBufferSize
,
94 OUT UINT32
*ExtraStackSize
97 ASSERT (RealModeBufferSize
!= NULL
);
98 ASSERT (ExtraStackSize
!= NULL
);
100 *RealModeBufferSize
= m16Size
;
103 // Extra 4 bytes for return address, and another 4 bytes for mode transition
105 *ExtraStackSize
= sizeof (IA32_DWORD_REGS
) + 8;
109 Prepares all structures a code required to use AsmThunk16().
111 Prepares all structures and code required to use AsmThunk16().
113 If ThunkContext is NULL, then ASSERT().
115 @param ThunkContext A pointer to the context structure that describes the
116 16-bit real mode code to call.
122 OUT THUNK_CONTEXT
*ThunkContext
125 IA32_SEGMENT_DESCRIPTOR
*RealModeGdt
;
127 ASSERT (ThunkContext
!= NULL
);
128 ASSERT ((UINTN
)ThunkContext
->RealModeBuffer
< 0x100000);
129 ASSERT (ThunkContext
->RealModeBufferSize
>= m16Size
);
130 ASSERT ((UINTN
)ThunkContext
->RealModeBuffer
+ m16Size
<= 0x100000);
132 CopyMem (ThunkContext
->RealModeBuffer
, &m16Start
, m16Size
);
135 // Point RealModeGdt to the GDT to be used in transition
137 // RealModeGdt[0]: Reserved as NULL descriptor
138 // RealModeGdt[1]: Code Segment
139 // RealModeGdt[2]: Data Segment
140 // RealModeGdt[3]: Call Gate
142 RealModeGdt
= (IA32_SEGMENT_DESCRIPTOR
*)(
143 (UINTN
)ThunkContext
->RealModeBuffer
+ m16Gdt
);
146 // Update Code & Data Segment Descriptor
148 RealModeGdt
[1].Bits
.BaseLow
=
149 (UINT32
)(UINTN
)ThunkContext
->RealModeBuffer
& ~0xf;
150 RealModeGdt
[1].Bits
.BaseMid
=
151 (UINT32
)(UINTN
)ThunkContext
->RealModeBuffer
>> 16;
154 // Update transition code entry point offset
156 *(UINT32
*)((UINTN
)ThunkContext
->RealModeBuffer
+ mTransition
) +=
157 (UINT32
)(UINTN
)ThunkContext
->RealModeBuffer
& 0xf;
160 // Update Segment Limits for both Code and Data Segment Descriptors
162 if ((ThunkContext
->ThunkAttributes
& THUNK_ATTRIBUTE_BIG_REAL_MODE
) == 0) {
164 // Set segment limits to 64KB
166 RealModeGdt
[1].Bits
.LimitHigh
= 0;
167 RealModeGdt
[1].Bits
.G
= 0;
168 RealModeGdt
[2].Bits
.LimitHigh
= 0;
169 RealModeGdt
[2].Bits
.G
= 0;
173 // Update GDTBASE for this thunk context
175 *(VOID
**)((UINTN
)ThunkContext
->RealModeBuffer
+ m16GdtrBase
) = RealModeGdt
;
178 // Update Thunk Attributes
180 *(UINT32
*)((UINTN
)ThunkContext
->RealModeBuffer
+ mThunk16Attr
) =
181 ThunkContext
->ThunkAttributes
;
185 Transfers control to a 16-bit real mode entry point and returns the results.
187 Transfers control to a 16-bit real mode entry point and returns the results.
188 AsmPrepareThunk16() must be called with ThunkContext before this function is
189 used. This function must be called with interrupts disabled.
191 If ThunkContext is NULL, then ASSERT().
192 If AsmPrepareThunk16() was not previously called with ThunkContext, then ASSERT().
194 @param ThunkContext A pointer to the context structure that describes the
195 16-bit real mode code to call.
201 IN OUT THUNK_CONTEXT
*ThunkContext
204 IA32_REGISTER_SET
*UpdatedRegs
;
206 ASSERT (ThunkContext
!= NULL
);
207 ASSERT ((UINTN
)ThunkContext
->RealModeBuffer
< 0x100000);
208 ASSERT (ThunkContext
->RealModeBufferSize
>= m16Size
);
209 ASSERT ((UINTN
)ThunkContext
->RealModeBuffer
+ m16Size
<= 0x100000);
211 UpdatedRegs
= InternalAsmThunk16 (
212 ThunkContext
->RealModeState
,
213 ThunkContext
->RealModeBuffer
216 CopyMem (ThunkContext
->RealModeState
, UpdatedRegs
, sizeof (*UpdatedRegs
));
220 Prepares all structures and code for a 16-bit real mode thunk, transfers
221 control to a 16-bit real mode entry point, and returns the results.
223 Prepares all structures and code for a 16-bit real mode thunk, transfers
224 control to a 16-bit real mode entry point, and returns the results. If the
225 caller only need to perform a single 16-bit real mode thunk, then this
226 service should be used. If the caller intends to make more than one 16-bit
227 real mode thunk, then it is more efficient if AsmPrepareThunk16() is called
228 once and AsmThunk16() can be called for each 16-bit real mode thunk. This
229 function must be called with interrupts disabled.
231 If ThunkContext is NULL, then ASSERT().
233 @param ThunkContext A pointer to the context structure that describes the
234 16-bit real mode code to call.
239 AsmPrepareAndThunk16 (
240 IN OUT THUNK_CONTEXT
*ThunkContext
243 AsmPrepareThunk16 (ThunkContext
);
244 AsmThunk16 (ThunkContext
);