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https://github.com/TomHarte/CLK.git
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111 lines
2.3 KiB
C++
111 lines
2.3 KiB
C++
//
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// Descriptors.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 19/03/2025.
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// Copyright © 2025 Thomas Harte. All rights reserved.
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//
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#pragma once
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#include "Instruction.hpp"
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namespace InstructionSet::x86 {
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enum class DescriptorTable {
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Global, Local, Interrupt,
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};
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struct DescriptorTablePointer {
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uint16_t limit;
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uint32_t base;
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};
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struct Descriptor {
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void set_segment(const uint16_t segment) {
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base_ = uint32_t(segment) << 4;
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limit_ = 0xffff;
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present_ = true;
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}
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void set(const uint16_t descriptor[4]) {
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base_ = uint32_t(descriptor[1] | ((descriptor[2] & 0xff) << 16));
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limit_ = descriptor[0];
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printf("%04x %04x %04x %04x\n", descriptor[0], descriptor[1], descriptor[2], descriptor[3]);
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present_ = descriptor[2] & 0x8000;
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privilege_level_ = (descriptor[2] >> 13) & 3;
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// TODO: need to know more about the below.
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if(descriptor[2] & 0x1000) {
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executable_ = descriptor[2] & 0x800;
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if(executable_) {
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conforming_ = descriptor[2] & 0x400;
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readable_ = descriptor[2] & 0x200;
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} else {
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// expand down = descriptor[2] & 0x400;
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// writeable_ = descriptor[2] & 0x200;
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}
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} else {
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assert(false);
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}
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}
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uint32_t to_linear(const uint32_t address) const {
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return base_ + address;
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}
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uint32_t base() const { return base_; }
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uint32_t limit() const { return limit_; }
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int privilege_level() const {
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return privilege_level_;
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}
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private:
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uint32_t base_;
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uint32_t limit_;
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// TODO: permissions, type, etc.
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int privilege_level_;
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enum class Type {
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AvailableTaskStateSegment = 1,
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LDTDescriptor = 2,
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BusyTaskStateSegment = 3,
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Invalid0 = 0, Invalid8 = 8,
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Control4 = 4, Control5 = 5, Control6 = 6, Control7 = 7,
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Reserved9 = 9, ReservedA = 10, ReservedB = 11, ReservedC = 12,
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ReservedD = 13, ReservedE = 14, ReservedF = 15,
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} type_;
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bool present_;
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bool readable_;
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bool conforming_;
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bool executable_;
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};
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template <typename SegmentT>
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struct SegmentRegisterSet {
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SegmentT &operator[](const Source segment) {
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return values_[index_of(segment)];
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}
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const SegmentT &operator[](const Source segment) const {
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return values_[index_of(segment)];
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}
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private:
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std::array<SegmentT, 6> values_;
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static constexpr size_t index_of(const Source segment) {
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assert(is_segment_register(segment));
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return size_t(segment) - size_t(Source::ES);
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}
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};
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}
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