\r
**/\r
\r
+//\r
+// Byte packed structure for a segment descriptor in a GDT/LDT\r
+//\r
+typedef union {\r
+ struct {\r
+ UINT32 LimitLow:16;\r
+ UINT32 BaseLow:16;\r
+ UINT32 BaseMid:8;\r
+ UINT32 Type:4;\r
+ UINT32 S:1;\r
+ UINT32 DPL:2;\r
+ UINT32 P:1;\r
+ UINT32 LimitHigh:4;\r
+ UINT32 AVL:1;\r
+ UINT32 L:1;\r
+ UINT32 DB:1;\r
+ UINT32 G:1;\r
+ UINT32 BaseHigh:8;\r
+ } Bits;\r
+ UINT64 Uint64;\r
+} IA32_SEGMENT_DESCRIPTOR;\r
+\r
+extern CONST UINT8 m16Start;\r
+extern CONST UINT16 m16Size;\r
+extern CONST UINT16 mThunk16Attr;\r
+extern CONST UINT16 m16Gdt;\r
+extern CONST UINT16 m16GdtrBase;\r
+extern CONST UINT16 mTransition;\r
+\r
/**\r
Invokes 16-bit code in big real mode and returns the updated register set.\r
\r
on the real mode stack and the starting address of the save area is returned.\r
\r
@param RegisterSet Values of registers before invocation of 16-bit code.\r
- @param Patch Pointer to the area following the 16-bit code.\r
+ @param Transition Pointer to the transition code under 1MB.\r
\r
@return The pointer to a IA32_REGISTER_SET structure containing the updated\r
register values.\r
IA32_REGISTER_SET *\r
InternalAsmThunk16 (\r
IN IA32_REGISTER_SET *RegisterSet,\r
- IN OUT VOID *Patch\r
+ IN OUT VOID *Transition\r
);\r
\r
+/**\r
+ Retrieves the properties for 16-bit thunk functions.\r
+\r
+ Computes the size of the buffer and stack below 1MB required to use the\r
+ AsmPrepareThunk16(), AsmThunk16() and AsmPrepareAndThunk16() functions. This\r
+ buffer size is returned in RealModeBufferSize, and the stack size is returned\r
+ in ExtraStackSize. If parameters are passed to the 16-bit real mode code,\r
+ then the actual minimum stack size is ExtraStackSize plus the maximum number\r
+ of bytes that need to be passed to the 16-bit real mode code.\r
+\r
+ If RealModeBufferSize is NULL, then ASSERT().\r
+ If ExtraStackSize is NULL, then ASSERT().\r
+\r
+ @param RealModeBufferSize A pointer to the size of the buffer below 1MB\r
+ required to use the 16-bit thunk functions.\r
+ @param ExtraStackSize A pointer to the extra size of stack below 1MB\r
+ that the 16-bit thunk functions require for\r
+ temporary storage in the transition to and from\r
+ 16-bit real mode.\r
+\r
+**/\r
+VOID\r
+EFIAPI\r
+AsmGetThunk16Properties (\r
+ OUT UINT32 *RealModeBufferSize,\r
+ OUT UINT32 *ExtraStackSize\r
+ )\r
+{\r
+ ASSERT (RealModeBufferSize != NULL);\r
+ ASSERT (ExtraStackSize != NULL);\r
+\r
+ *RealModeBufferSize = m16Size;\r
+ *ExtraStackSize = sizeof (IA32_DWORD_REGS) + 8;\r
+}\r
+\r
/**\r
Prepares all structures a code required to use AsmThunk16().\r
\r
OUT THUNK_CONTEXT *ThunkContext\r
)\r
{\r
+ IA32_SEGMENT_DESCRIPTOR *RealModeGdt;\r
+\r
ASSERT (ThunkContext != NULL);\r
+ ASSERT ((UINTN)ThunkContext->RealModeBuffer < 0x100000);\r
+ ASSERT (ThunkContext->RealModeBufferSize >= m16Size);\r
+ ASSERT ((UINTN)ThunkContext->RealModeBuffer + m16Size <= 0x100000);\r
+\r
+ CopyMem (ThunkContext->RealModeBuffer, &m16Start, m16Size);\r
+\r
+ //\r
+ // Point RealModeGdt to the GDT to be used in transition\r
+ //\r
+ // RealModeGdt[0]: Reserved as NULL descriptor\r
+ // RealModeGdt[1]: Code Segment\r
+ // RealModeGdt[2]: Data Segment\r
+ // RealModeGdt[3]: Call Gate\r
+ //\r
+ RealModeGdt = (IA32_SEGMENT_DESCRIPTOR*)(\r
+ (UINTN)ThunkContext->RealModeBuffer + m16Gdt);\r
+\r
+ //\r
+ // Update Code & Data Segment Descriptor\r
+ //\r
+ RealModeGdt[1].Bits.BaseLow =\r
+ (UINT32)(UINTN)ThunkContext->RealModeBuffer & ~0xf;\r
+ RealModeGdt[1].Bits.BaseMid =\r
+ (UINT32)(UINTN)ThunkContext->RealModeBuffer >> 16;\r
+\r
+ //\r
+ // Update transition code entry point offset\r
+ //\r
+ *(UINT32*)((UINTN)ThunkContext->RealModeBuffer + mTransition) +=\r
+ (UINT32)(UINTN)ThunkContext->RealModeBuffer & 0xf;\r
+\r
+ //\r
+ // Update Segment Limits for both Code and Data Segment Descriptors\r
+ //\r
+ if ((ThunkContext->ThunkAttributes & THUNK_ATTRIBUTE_BIG_REAL_MODE) == 0) {\r
+ //\r
+ // Set segment limits to 64KB\r
+ //\r
+ RealModeGdt[1].Bits.LimitHigh = 0;\r
+ RealModeGdt[1].Bits.G = 0;\r
+ RealModeGdt[2].Bits.LimitHigh = 0;\r
+ RealModeGdt[2].Bits.G = 0;\r
+ }\r
+\r
+ //\r
+ // Update GDTBASE for this thunk context\r
+ //\r
+ *(VOID**)((UINTN)ThunkContext->RealModeBuffer + m16GdtrBase) = RealModeGdt;\r
+\r
+ //\r
+ // Update Thunk Attributes\r
+ //\r
+ *(UINT32*)((UINTN)ThunkContext->RealModeBuffer + mThunk16Attr) =\r
+ ThunkContext->ThunkAttributes;\r
}\r
\r
/**\r
IN OUT THUNK_CONTEXT *ThunkContext\r
)\r
{\r
- UINT16 *Patch;\r
+ IA32_REGISTER_SET *UpdatedRegs;\r
\r
ASSERT (ThunkContext != NULL);\r
+ ASSERT ((UINTN)ThunkContext->RealModeBuffer < 0x100000);\r
+ ASSERT (ThunkContext->RealModeBufferSize >= m16Size);\r
+ ASSERT ((UINTN)ThunkContext->RealModeBuffer + m16Size <= 0x100000);\r
\r
- Patch = (UINT16*)(\r
- (UINTN)ThunkContext->RealModeCode +\r
- ThunkContext->RealModeCodeSize\r
- );\r
+ UpdatedRegs = InternalAsmThunk16 (\r
+ ThunkContext->RealModeState,\r
+ ThunkContext->RealModeBuffer\r
+ );\r
\r
- //\r
- // 0x9a66 is the OpCode of far call with an operand size override.\r
- //\r
- *Patch = 0x9a66;\r
-\r
- //\r
- // CopyMem() here copies the updated register values back to RealModeState\r
- //\r
- CopyMem (\r
- &ThunkContext->RealModeState,\r
- InternalAsmThunk16 (&ThunkContext->RealModeState, Patch + 1),\r
- sizeof (ThunkContext->RealModeState)\r
- );\r
+ CopyMem (ThunkContext->RealModeState, UpdatedRegs, sizeof (*UpdatedRegs));\r
}\r
\r
/**\r
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