os: rework kernel architecture

Rework the code structure and architecture of the kernel by separating
platform-dependent and platform-independent code more cleanly. As of
this patchset, full feature parity has not been achieved. Nonetheless, a
sufficient subset of functionality has been ported to the new
architecture to demonstrate the feasibility of the new structure.

72 files changed, 3573 insertions, 0 deletions

diff --git a/arch/x86_64/pre/include/arch/context_switching/interrupt_descriptor_table/gate_descriptor.hpp b/arch/x86_64/pre/include/arch/context_switching/interrupt_descriptor_table/gate_descriptor.hpp
new file mode 100644
index 0000000..07110c8
--- /dev/null
+++ b/arch/x86_64/pre/include/arch/context_switching/interrupt_descriptor_table/gate_descriptor.hpp
@@ -0,0 +1,69 @@
+#ifndef TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_INTERRUPT_DESCRIPTOR_TABLE_GATE_DESCRIPTOR_HPP
+#define TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_INTERRUPT_DESCRIPTOR_TABLE_GATE_DESCRIPTOR_HPP
+
+#include "arch/context_switching/interrupt_descriptor_table/idt_flags.hpp"
+#include "arch/context_switching/interrupt_descriptor_table/ist_offset.hpp"
+#include "arch/context_switching/interrupt_descriptor_table/segment_selector.hpp"
+
+#include <bitset>
+#include <cstdint>
+
+namespace teachos::arch::context_switching::interrupt_descriptor_table
+{
+  __extension__ typedef __int128 int128_t;
+  __extension__ typedef unsigned __int128 uint128_t;
+
+  /**
+   * @brief Defines helper function for all states and the actual data the gate descriptor can have.
+   */
+  struct [[gnu::packed]] gate_descriptor
+  {
+    /**
+     * @brief Default Constructor.
+     */
+    gate_descriptor() = default;
+
+    /**
+     * @brief Constructor.
+     *
+     * @note Created gate descriptor copies the given bytes into these components ending with a 32 bit reserved
+     * field that has to be used, because the 64-bit gate descriptor needs to be big enough for two 32-bit gate
+     * descriptor.
+     * - 16 bit Segment Selector
+     * - 3 bit Interrupt Stack Table Offset
+     * - 8 bit Type and Flags
+     * - 64 bit Offset
+     *
+     * @param flags Copies the bits set from the given data into the individual components of a gate
+     * descriptor.
+     */
+    explicit gate_descriptor(uint128_t flags);
+
+    /**
+     * @brief Constructor.
+     *
+     * @param selector, ist, flags, offset Copies the bits set from the given data into the individual components of
+     * a gate descriptor.
+     */
+    gate_descriptor(segment_selector selector, ist_offset ist, idt_flags flags, uint64_t offset);
+
+    /**
+     * @brief Allows to compare the underlying bits of two instances.
+     *
+     * @param other Other instance that we want to compare with.
+     * @return Whether the underlying set bits of both types are the same.
+     */
+    auto operator==(gate_descriptor const & other) const -> bool = default;
+
+  private:
+    // The order in private variables starts for the first variable being the rightmost bit.
+    uint16_t _offset_1 = {};          ///< Lower 16 bits of handler function address (0 - 15)
+    segment_selector _selector = {};  ///< Segment selector (16 - 31)
+    ist_offset _ist = {};             ///< Interrupt Stack Table offset (32 - 39)
+    idt_flags _flags = {};            ///< Gate Type and Flags (40 - 47)
+    uint64_t _offset_2 : 48 = {};     ///< Upper 48 bits of handler function address (48 - 95)
+    uint32_t : 32;                    ///< Reserved field used to ensure this struct is 128 bits big (96 - 127)
+  };
+}  // namespace teachos::arch::context_switching::interrupt_descriptor_table
+
+#endif  // TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_INTERRUPT_DESCRIPTOR_TABLE_GATE_DESCRIPTOR_HPP
diff --git a/arch/x86_64/pre/include/arch/context_switching/interrupt_descriptor_table/idt_flags.hpp b/arch/x86_64/pre/include/arch/context_switching/interrupt_descriptor_table/idt_flags.hpp
new file mode 100644
index 0000000..5104c36
--- /dev/null
+++ b/arch/x86_64/pre/include/arch/context_switching/interrupt_descriptor_table/idt_flags.hpp
@@ -0,0 +1,81 @@
+
+#ifndef TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_INTERRUPT_DESCRIPTOR_TABLE_IDT_FLAGS_HPP
+#define TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_INTERRUPT_DESCRIPTOR_TABLE_IDT_FLAGS_HPP
+
+#include <bitset>
+#include <cstdint>
+
+namespace teachos::arch::context_switching::interrupt_descriptor_table
+{
+  /**
+   * @brief Defines helper function for all states that the access byte field of a segment descriptor can
+   * have.
+   */
+  struct [[gnu::packed]] idt_flags
+  {
+    /**
+     * @brief Possible set bits in our underlying bits and the meaning when they are set.
+     */
+    enum bitset : uint8_t
+    {
+      INTERRUPT_GATE = 0b01110,  ///< The actual type of gate segment is a interrupt gate.
+      TRAP_GATE = 0b01111,       ///< The actual type of gate segment is a trap gate.
+      DESCRIPTOR_LEVEL_KERNEL =
+          0U << 5U,  ///< Highest privileged level used by the kernel to allow for full access of resources.
+      DESCRIPTOR_LEVEL_ADMIN =
+          1U << 5U,  ///< Restricts access to own application and thoose of lower privilege. Should only be used if more
+                     ///< than two privilege levels are required, otherwise using Level 3 and Level 0 is recommended.
+      DESCRIPTOR_LEVEL_PRIVILEGED_USER =
+          2U << 5U,  ///< Restricts access to own application and thoose of lower privilege. Should only be used if more
+                     ///< than two privilege levels are required, otherwise using Level 3 and Level 0 is recommended.
+      DESCRIPTOR_LEVEL_USER = 3U << 5U,  ///< Restricts access to only application and their specific memory.
+      PRESENT = 1U << 7U,                ///< Present bit; Allows an entry to refer to a valid segment.
+                                         ///< Must be set (1) for any valid segment.
+    };
+
+    /**
+     * @brief Default Constructor.
+     */
+    idt_flags() = default;
+
+    /**
+     * @brief Constructor.
+     *
+     * @param flags Allows to set flags for the access byte field using the unscoped enum contained in this class, used
+     * to allow for direct integer conversion. This value is saved and can later be used to check whether certain flags
+     * are enabled or not using contains_flags method.
+     */
+    idt_flags(uint8_t flags);
+
+    /**
+     * @brief Checks if the given std::bitset is a subset or equivalent to the underlying data.
+     *
+     * @note Meaning that all bits that are set in the given std::bitset also have to be set in the underlyng
+     * data. Any additional bits that are set are not relevant.
+     *
+     * @param other Flags that we want to compare against and check if the underlying data has the same bits set.
+     * @return Whether the given flags are a subset or equivalent with the underlying data.
+     */
+    auto contains_flags(std::bitset<8U> other) const -> bool;
+
+    /**
+     * @brief Allows to compare the underlying bits of two instances.
+     *
+     * @param other Other instance that we want to compare with.
+     * @return Whether the underlying set bits of both types are the same.
+     */
+    auto operator==(idt_flags const & other) const -> bool = default;
+
+    /**
+     * @brief Combines all bits that are set in the std::bitset flags with the bits already set in the underlying data.
+     *
+     * @param other Additional bits that should be set.
+     */
+    auto operator|=(std::bitset<8U> other) -> void;
+
+  private:
+    uint8_t _flags = {};  ///< Underlying bits used to read the flags from.
+  };
+}  // namespace teachos::arch::context_switching::interrupt_descriptor_table
+
+#endif  // TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_INTERRUPT_DESCRIPTOR_TABLE_IDT_FLAGS_HPP
\ No newline at end of file
diff --git a/arch/x86_64/pre/include/arch/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.hpp b/arch/x86_64/pre/include/arch/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.hpp
new file mode 100644
index 0000000..b388e0e
--- /dev/null
+++ b/arch/x86_64/pre/include/arch/context_switching/interrupt_descriptor_table/interrupt_descriptor_table.hpp
@@ -0,0 +1,24 @@
+#ifndef TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_INTERRUPT_DESCRIPTOR_TABLE_INTERRUPT_DESCRIPTOR_TABLE_HPP
+#define TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_INTERRUPT_DESCRIPTOR_TABLE_INTERRUPT_DESCRIPTOR_TABLE_HPP
+
+#include "arch/context_switching/interrupt_descriptor_table/interrupt_descriptor_table_pointer.hpp"
+
+namespace teachos::arch::context_switching::interrupt_descriptor_table
+{
+  /**
+   * @brief Updates the IDTR with the created interrupt descriptor table. If it has not been created yet this
+   * method will create it.
+   */
+  auto update_interrupt_descriptor_table_register() -> void;
+
+  /**
+   * @brief Creates the interrupt descriptor table, with the minimum required configuration. If this method is called
+   * more than once, the previously created instance is returned instead.
+   *
+   * @return Reference to the created interrupt_descriptor_table.
+   */
+  auto get_or_create_interrupt_descriptor_table() -> interrupt_descriptor_table &;
+
+}  // namespace teachos::arch::context_switching::interrupt_descriptor_table
+
+#endif  // TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_INTERRUPT_DESCRIPTOR_TABLE_INTERRUPT_DESCRIPTOR_TABLE_HPP
diff --git a/arch/x86_64/pre/include/arch/context_switching/interrupt_descriptor_table/interrupt_descriptor_table_pointer.hpp b/arch/x86_64/pre/include/arch/context_switching/interrupt_descriptor_table/interrupt_descriptor_table_pointer.hpp
new file mode 100644
index 0000000..7fe933b
--- /dev/null
+++ b/arch/x86_64/pre/include/arch/context_switching/interrupt_descriptor_table/interrupt_descriptor_table_pointer.hpp
@@ -0,0 +1,40 @@
+#ifndef TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_INTERRUPT_DESCRIPTOR_TABLE_INTERRUPT_DESCRIPTOR_TABLE_POINTER_HPP
+#define TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_INTERRUPT_DESCRIPTOR_TABLE_INTERRUPT_DESCRIPTOR_TABLE_POINTER_HPP
+
+#include "arch/context_switching/interrupt_descriptor_table/gate_descriptor.hpp"
+#include "arch/stl/vector.hpp"
+
+namespace teachos::arch::context_switching::interrupt_descriptor_table
+{
+  using interrupt_descriptor_table = stl::vector<gate_descriptor>;
+
+  /**
+   * @brief Represents a pointer to the Interrupt Descriptor Table (IDT).
+   *
+   * This structure is used to store the base address and length of the IDT.
+   */
+  struct [[gnu::packed]] interrupt_descriptor_table_pointer
+  {
+    /**
+     * @brief Default constructor.
+     */
+    interrupt_descriptor_table_pointer() = default;
+
+    /**
+     * @brief Constructor.
+     */
+    interrupt_descriptor_table_pointer(uint16_t table_length, gate_descriptor * address);
+
+    /**
+     * @brief Defaulted three-way comparsion operator.
+     */
+    auto operator<=>(interrupt_descriptor_table_pointer const & other) const -> std::strong_ordering = default;
+
+  private:
+    uint16_t table_length = {};      ///< The amount of segment descriptor entries in the global descriptor table - 1.
+    gate_descriptor * address = {};  ///< Non-owning pointer to the IDT base address.
+  };
+
+}  // namespace teachos::arch::context_switching::interrupt_descriptor_table
+
+#endif  // TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_INTERRUPT_DESCRIPTOR_TABLE_INTERRUPT_DESCRIPTOR_TABLE_POINTER_HPP
diff --git a/arch/x86_64/pre/include/arch/context_switching/interrupt_descriptor_table/ist_offset.hpp b/arch/x86_64/pre/include/arch/context_switching/interrupt_descriptor_table/ist_offset.hpp
new file mode 100644
index 0000000..e45bcf4
--- /dev/null
+++ b/arch/x86_64/pre/include/arch/context_switching/interrupt_descriptor_table/ist_offset.hpp
@@ -0,0 +1,45 @@
+#ifndef TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_INTERRUPT_DESCRIPTOR_TABLE_IST_OFFSET_HPP
+#define TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_INTERRUPT_DESCRIPTOR_TABLE_IST_OFFSET_HPP
+
+#include <bitset>
+#include <cstdint>
+
+namespace teachos::arch::context_switching::interrupt_descriptor_table
+{
+  /**
+   * @brief Defines helper function for all states that the interrupt stack table offset field of a gate descriptor can
+   * have. Is automatically increased to one byte in size, to include the following 5 reserved bits in the gate
+   * descriptor.
+   */
+  struct [[gnu::packed]] ist_offset
+  {
+    /**
+     * @brief Default Constructor.
+     */
+    ist_offset() = default;
+
+    /**
+     * @brief Constructor.
+     *
+     * @param offset Offset into the interrupt stack table. A value of of 0 means we do not switch stacks, whereas 1 - 7
+     * mean we switch to the n-th stack in the Interrupt Stack Table, contained in the TSS if the gate descriptor that
+     * contains this field is called.
+     */
+    ist_offset(uint8_t offset);
+
+    /**
+     * @brief Allows to compare the underlying set bits of two instances.
+     *
+     * @param other Other instance that we want to compare with.
+     * @return Whether the underlying set bits of both types are the same.
+     */
+    auto operator==(ist_offset const & other) const -> bool = default;
+
+  private:
+    uint8_t _ist : 3 = {};  ///< Offset into the interrupt stack table. A value of of 0 means we do not switch stacks,
+                            ///< whereas 1 - 7 mean we switch to the n-th stack in the Interrupt Stack Table, contained
+                            ///< in the TSS if the gate descriptor that contains this field is called.
+  };
+}  // namespace teachos::arch::context_switching::interrupt_descriptor_table
+
+#endif  // TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_INTERRUPT_DESCRIPTOR_TABLE_IST_OFFSET_HPP
diff --git a/arch/x86_64/pre/include/arch/context_switching/interrupt_descriptor_table/segment_selector.hpp b/arch/x86_64/pre/include/arch/context_switching/interrupt_descriptor_table/segment_selector.hpp
new file mode 100644
index 0000000..ea8c145
--- /dev/null
+++ b/arch/x86_64/pre/include/arch/context_switching/interrupt_descriptor_table/segment_selector.hpp
@@ -0,0 +1,105 @@
+#ifndef TEACHOS_ARCH_X86_64_CONTEXT_SWITCHING_INTERRUPT_DESCRIPTOR_TABLE_SEGMENT_SELECTOR