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72 lines
2.5 KiB
C
72 lines
2.5 KiB
C
/** @file
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AsmDisablePaging32 function.
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Copyright (c) 2006 - 2008, Intel Corporation. All rights reserved.<BR>
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SPDX-License-Identifier: BSD-2-Clause-Patent
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**/
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#include "BaseLibInternals.h"
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/**
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Disables the 32-bit paging mode on the CPU.
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Disables the 32-bit paging mode on the CPU and returns to 32-bit protected
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mode. This function assumes the current execution mode is 32-paged protected
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mode. This function is only available on IA-32. After the 32-bit paging mode
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is disabled, control is transferred to the function specified by EntryPoint
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using the new stack specified by NewStack and passing in the parameters
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specified by Context1 and Context2. Context1 and Context2 are optional and
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may be NULL. The function EntryPoint must never return.
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There are a number of constraints that must be followed before calling this
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function:
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1) Interrupts must be disabled.
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2) The caller must be in 32-bit paged mode.
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3) CR0, CR3, and CR4 must be compatible with 32-bit paged mode.
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4) CR3 must point to valid page tables that guarantee that the pages for
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this function and the stack are identity mapped.
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@param EntryPoint A pointer to function to call with the new stack after
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paging is disabled.
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@param Context1 A pointer to the context to pass into the EntryPoint
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function as the first parameter after paging is disabled.
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@param Context2 A pointer to the context to pass into the EntryPoint
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function as the second parameter after paging is
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disabled.
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@param NewStack A pointer to the new stack to use for the EntryPoint
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function after paging is disabled.
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**/
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__declspec (naked)
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VOID
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EFIAPI
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InternalX86DisablePaging32 (
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IN SWITCH_STACK_ENTRY_POINT EntryPoint,
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IN VOID *Context1, OPTIONAL
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IN VOID *Context2, OPTIONAL
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IN VOID *NewStack
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)
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{
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_asm {
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push ebp
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mov ebp, esp
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mov ebx, EntryPoint
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mov ecx, Context1
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mov edx, Context2
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pushfd
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pop edi // save EFLAGS to edi
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cli
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mov eax, cr0
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btr eax, 31
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mov esp, NewStack
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mov cr0, eax
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push edi
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popfd // restore EFLAGS from edi
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push edx
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push ecx
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call ebx
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jmp $ // EntryPoint() should not return
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}
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}
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