Removed unnecessary ASSERT condition (assertion of real mode buffers' alignment)
[mirror_edk2.git] / MdePkg / Library / BaseLib / x86Thunk.c
1 /** @file
2 Real Mode Thunk Functions for IA32 and X64.
3
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
9
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.
12
13 Module Name: x86Thunk.c
14
15 **/
16
17 //
18 // Byte packed structure for a segment descriptor in a GDT/LDT
19 //
20 typedef union {
21 struct {
22 UINT32 LimitLow:16;
23 UINT32 BaseLow:16;
24 UINT32 BaseMid:8;
25 UINT32 Type:4;
26 UINT32 S:1;
27 UINT32 DPL:2;
28 UINT32 P:1;
29 UINT32 LimitHigh:4;
30 UINT32 AVL:1;
31 UINT32 L:1;
32 UINT32 DB:1;
33 UINT32 G:1;
34 UINT32 BaseHigh:8;
35 } Bits;
36 UINT64 Uint64;
37 } IA32_SEGMENT_DESCRIPTOR;
38
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;
45
46 /**
47 Invokes 16-bit code in big real mode and returns the updated register set.
48
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.
52
53 @param RegisterSet Values of registers before invocation of 16-bit code.
54 @param Transition Pointer to the transition code under 1MB.
55
56 @return The pointer to a IA32_REGISTER_SET structure containing the updated
57 register values.
58
59 **/
60 IA32_REGISTER_SET *
61 InternalAsmThunk16 (
62 IN IA32_REGISTER_SET *RegisterSet,
63 IN OUT VOID *Transition
64 );
65
66 /**
67 Retrieves the properties for 16-bit thunk functions.
68
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.
75
76 If RealModeBufferSize is NULL, then ASSERT().
77 If ExtraStackSize is NULL, then ASSERT().
78
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
84 16-bit real mode.
85
86 **/
87 VOID
88 EFIAPI
89 AsmGetThunk16Properties (
90 OUT UINT32 *RealModeBufferSize,
91 OUT UINT32 *ExtraStackSize
92 )
93 {
94 ASSERT (RealModeBufferSize != NULL);
95 ASSERT (ExtraStackSize != NULL);
96
97 *RealModeBufferSize = m16Size;
98 *ExtraStackSize = sizeof (IA32_DWORD_REGS) + 8;
99 }
100
101 /**
102 Prepares all structures a code required to use AsmThunk16().
103
104 Prepares all structures and code required to use AsmThunk16().
105
106 If ThunkContext is NULL, then ASSERT().
107
108 @param ThunkContext A pointer to the context structure that describes the
109 16-bit real mode code to call.
110
111 **/
112 VOID
113 EFIAPI
114 AsmPrepareThunk16 (
115 OUT THUNK_CONTEXT *ThunkContext
116 )
117 {
118 IA32_SEGMENT_DESCRIPTOR *RealModeGdt;
119
120 ASSERT (ThunkContext != NULL);
121 ASSERT ((UINTN)ThunkContext->RealModeBuffer < 0x100000);
122 ASSERT (ThunkContext->RealModeBufferSize >= m16Size);
123 ASSERT ((UINTN)ThunkContext->RealModeBuffer + m16Size <= 0x100000);
124
125 CopyMem (ThunkContext->RealModeBuffer, &m16Start, m16Size);
126
127 //
128 // Point RealModeGdt to the GDT to be used in transition
129 //
130 // RealModeGdt[0]: Reserved as NULL descriptor
131 // RealModeGdt[1]: Code Segment
132 // RealModeGdt[2]: Data Segment
133 // RealModeGdt[3]: Call Gate
134 //
135 RealModeGdt = (IA32_SEGMENT_DESCRIPTOR*)(
136 (UINTN)ThunkContext->RealModeBuffer + m16Gdt);
137
138 //
139 // Update Code & Data Segment Descriptor
140 //
141 RealModeGdt[1].Bits.BaseLow =
142 (UINT32)(UINTN)ThunkContext->RealModeBuffer & ~0xf;
143 RealModeGdt[1].Bits.BaseMid =
144 (UINT32)(UINTN)ThunkContext->RealModeBuffer >> 16;
145
146 //
147 // Update transition code entry point offset
148 //
149 *(UINT32*)((UINTN)ThunkContext->RealModeBuffer + mTransition) +=
150 (UINT32)(UINTN)ThunkContext->RealModeBuffer & 0xf;
151
152 //
153 // Update Segment Limits for both Code and Data Segment Descriptors
154 //
155 if ((ThunkContext->ThunkAttributes & THUNK_ATTRIBUTE_BIG_REAL_MODE) == 0) {
156 //
157 // Set segment limits to 64KB
158 //
159 RealModeGdt[1].Bits.LimitHigh = 0;
160 RealModeGdt[1].Bits.G = 0;
161 RealModeGdt[2].Bits.LimitHigh = 0;
162 RealModeGdt[2].Bits.G = 0;
163 }
164
165 //
166 // Update GDTBASE for this thunk context
167 //
168 *(VOID**)((UINTN)ThunkContext->RealModeBuffer + m16GdtrBase) = RealModeGdt;
169
170 //
171 // Update Thunk Attributes
172 //
173 *(UINT32*)((UINTN)ThunkContext->RealModeBuffer + mThunk16Attr) =
174 ThunkContext->ThunkAttributes;
175 }
176
177 /**
178 Transfers control to a 16-bit real mode entry point and returns the results.
179
180 Transfers control to a 16-bit real mode entry point and returns the results.
181 AsmPrepareThunk16() must be called with ThunkContext before this function is
182 used. This function must be called with interrupts disabled.
183
184 If ThunkContext is NULL, then ASSERT().
185 If AsmPrepareThunk16() was not previously called with ThunkContext, then ASSERT().
186
187 @param ThunkContext A pointer to the context structure that describes the
188 16-bit real mode code to call.
189
190 **/
191 VOID
192 EFIAPI
193 AsmThunk16 (
194 IN OUT THUNK_CONTEXT *ThunkContext
195 )
196 {
197 IA32_REGISTER_SET *UpdatedRegs;
198
199 ASSERT (ThunkContext != NULL);
200 ASSERT ((UINTN)ThunkContext->RealModeBuffer < 0x100000);
201 ASSERT (ThunkContext->RealModeBufferSize >= m16Size);
202 ASSERT ((UINTN)ThunkContext->RealModeBuffer + m16Size <= 0x100000);
203
204 UpdatedRegs = InternalAsmThunk16 (
205 ThunkContext->RealModeState,
206 ThunkContext->RealModeBuffer
207 );
208
209 CopyMem (ThunkContext->RealModeState, UpdatedRegs, sizeof (*UpdatedRegs));
210 }
211
212 /**
213 Prepares all structures and code for a 16-bit real mode thunk, transfers
214 control to a 16-bit real mode entry point, and returns the results.
215
216 Prepares all structures and code for a 16-bit real mode thunk, transfers
217 control to a 16-bit real mode entry point, and returns the results. If the
218 caller only need to perform a single 16-bit real mode thunk, then this
219 service should be used. If the caller intends to make more than one 16-bit
220 real mode thunk, then it is more efficient if AsmPrepareThunk16() is called
221 once and AsmThunk16() can be called for each 16-bit real mode thunk. This
222 function must be called with interrupts disabled.
223
224 If ThunkContext is NULL, then ASSERT().
225
226 @param ThunkContext A pointer to the context structure that describes the
227 16-bit real mode code to call.
228
229 **/
230 VOID
231 EFIAPI
232 AsmPrepareAndThunk16 (
233 IN OUT THUNK_CONTEXT *ThunkContext
234 )
235 {
236 AsmPrepareThunk16 (ThunkContext);
237 AsmThunk16 (ThunkContext);
238 }