248 lines
7.2 KiB
C
248 lines
7.2 KiB
C
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/* -*- Mode: C; c-basic-offset: 3 -*-
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*
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* bios.c - Make real-mode BIOS calls from protected mode.
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* For simplicity and small size, this implementation
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* switches back to real-mode rather than using virtual 8086
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* mode. A v86 mode implementation may be more robust.
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*
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* This file is part of Metalkit, a simple collection of modules for
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* writing software that runs on the bare metal. Get the latest code
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* at http://svn.navi.cx/misc/trunk/metalkit/
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*
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* Copyright (c) 2008-2009 Micah Dowty
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*
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* Permission is hereby granted, free of charge, to any person
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* obtaining a copy of this software and associated documentation
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* files (the "Software"), to deal in the Software without
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* restriction, including without limitation the rights to use,
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* copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the
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* Software is furnished to do so, subject to the following
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* conditions:
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*
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* The above copyright notice and this permission notice shall be
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* included in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
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* OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
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* HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
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* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
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* OTHER DEALINGS IN THE SOFTWARE.
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*/
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#include "bios.h"
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#include "boot.h"
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#include "intr.h"
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/*
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* BIOSCallInternal --
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*
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* Internal implementation of BIOS_Call. This is a C function which
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* wraps the assembly-language internal implementation. The only
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* reason to use C here, really, is so we can easily calculate
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* offsets into our shared C structures.
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*
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* This function must not make any function calls, since we need to
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* be able to trust the value of %esp. This is also why it must not
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* be inlined into BIOS_Call itself.
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*/
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static __attribute__((noinline)) void
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BIOSCallInternal(void)
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{
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/*
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* Save registers and stack in a safe place.
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*/
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asm volatile ("pusha");
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asm volatile ("mov %%esp, %0" :"=m" (BIOS_SHARED->esp));
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/*
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* Jump the the relocated 16-bit trampoline (source code below).
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*/
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asm volatile ("ljmp %0, %1"
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:: "i" (BOOT_CODE16_SEG), "i" (BIOS_SHARED->trampoline));
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/*
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* This is where we return from the relocated trampoline.
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* We're back in protected mode, but the data segments
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* are still 16-bit. Restore them.
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*/
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asm volatile ("BIOSReturn32: \n"
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"mov %0, %%ax \n"
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"mov %%ax, %%ss \n"
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"mov %%ax, %%ds \n"
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"mov %%ax, %%es \n"
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"mov %%ax, %%fs \n"
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"mov %%ax, %%gs \n"
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:: "i" (BOOT_DATA_SEG));
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/*
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* Restore our stack and saved registers.
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* Now we can safely execute C code again.
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*/
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asm volatile("mov %0, %%esp" ::"m" (BIOS_SHARED->esp));
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asm volatile ("popa");
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/*
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* Return here. The rest of this code is never run directly,
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* but we need to prevent GCC from optimizing it out.
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*/
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asm volatile("jmp BIOSTrampolineEnd\n");
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/*
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* This is a 16-bit assembly-language trampoline, relocated at
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* runtime to low memory, which actually makes the BIOS call. It
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* handles saving/restoring registers, and it switches in and out
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* of real mode.
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*
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* This code is never run directly.
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*/
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asm volatile("BIOSTrampoline: .code16");
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/*
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* Switch to our 16-bit data segment.
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*/
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asm volatile("movw %0, %%ax \n"
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"movw %%ax, %%ds \n"
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"movw %%ax, %%es \n"
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"movw %%ax, %%ss \n"
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:: "i" (BOOT_DATA16_SEG));
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/*
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* Disable protected mode.
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*/
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asm volatile("movl %cr0, %eax \n"
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"andl $(~1), %eax \n"
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"movl %eax, %cr0 \n");
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/*
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* Do another long jump to reset the real-mode %cs
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* register to a valid paragraph number. Right now
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* it's still a protected-mode-style selector index.
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*
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* XXX: I'm not sure how to do this address calculation cleanly.
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* Currently I'm hardcoding the address of the relocated trampoline.
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*/
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asm volatile("ljmp $0, $(BIOSTrampolineCS16 - BIOSTrampoline + 0x7C00)\n"
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"BIOSTrampolineCS16: \n");
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/*
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* Set up the real-mode stack and %cs register.
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*/
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asm volatile("xorw %%ax, %%ax \n"
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"mov %%ax, %%ss \n"
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"mov %0, %%esp \n"
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:: "i" (&BIOS_SHARED->stackTop[-sizeof(Regs)]));
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/*
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* Pop Regs off the stack.
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*/
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asm volatile("pop %ds \n"
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"pop %es \n"
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"pop %eax \n" // Ignore EFLAGS value.
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"popal \n");
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/*
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* This interrupt instruction is a placeholder that gets
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* patched at runtime (after relocation) to point to the
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* right interrupt vector.
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*/
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asm volatile("BIOSTrampolineVector: \n"
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"int $0xFF");
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/*
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* Push Regs back onto the stack.
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*/
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asm volatile("pushal \n"
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"pushfl \n"
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"push %es \n"
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"push %ds \n");
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/*
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* Enable protected mode.
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*/
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asm volatile("movl %cr0, %eax \n"
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"orl $1, %eax \n"
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"movl %eax, %cr0 \n");
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/*
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* Return via a long 16-to-32 bit jump.
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*/
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asm volatile("data32 ljmp %0, $BIOSReturn32 \n"
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:: "i" (BOOT_CODE_SEG));
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asm volatile("BIOSTrampolineEnd: .code32 \n");
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}
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extern struct {
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uint16 limit;
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uint32 base;
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} PACKED IDTDesc;
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/*
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* BIOS_Call --
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*
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* Make BIOS calls after boot, by temporarily switching
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* back into real mode.
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*
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* This function relocates the trampoline and stack into
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* real-mode-addressable low memory, then makes a 32-to-16-bit jump
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* into the trampoline.
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*/
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fastcall void
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BIOS_Call(uint8 vector, Regs *regs)
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{
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extern uint8 BIOSTrampoline[];
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extern uint8 BIOSTrampolineVector[];
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extern uint8 BIOSTrampolineEnd[];
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const uint32 trampSize = (uint8*)BIOSTrampolineEnd - (uint8*)BIOSTrampoline;
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const uint32 vectorOffset = (uint8*)BIOSTrampolineVector - (uint8*)BIOSTrampoline + 1;
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Bool iFlag = Intr_Save();
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Intr_Disable();
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/*
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* Relocate the trampoline code itself.
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*/
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memcpy(BIOS_SHARED->trampoline, BIOSTrampoline, trampSize);
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/*
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* Save the 32-bit IDT descriptor, and set up a legacy 256-entry
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* 16-bit IDT descriptor.
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*/
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asm volatile("sidt %0" : "=m" (BIOS_SHARED->idtr32));
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BIOS_SHARED->idtr16.base = 0;
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BIOS_SHARED->idtr16.limit = 0x3ff;
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asm volatile("lidt %0" :: "m" (BIOS_SHARED->idtr16));
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/*
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* Binary-patch the trampoline code with the right interrupt vector.
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*/
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BIOS_SHARED->trampoline[vectorOffset] = vector;
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/*
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* Copy Regs onto the top of the 16-bit stack.
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*/
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memcpy(&BIOS_SHARED->stackTop[-sizeof *regs], regs, sizeof *regs);
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BIOSCallInternal();
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/* Copy Regs back */
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memcpy(regs, &BIOS_SHARED->stackTop[-sizeof *regs], sizeof *regs);
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/*
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* Back to 32-bit IDT.
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*/
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asm volatile("lidt %0" :: "m" (BIOS_SHARED->idtr32));
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Intr_Restore(iFlag);
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}
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