Add files to cmake and implement gdt flags

4 files changed, 90 insertions, 0 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8657cab..3717788 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -116,6 +116,13 @@ add_library("_exception" OBJECT)
 add_library("teachos::exception" ALIAS "_exception")
 
 #[============================================================================[
+# The Context switching Library
+#]============================================================================]
+
+add_library("_context" OBJECT)
+add_library("teachos::context_switching" ALIAS "_context")
+
+#[============================================================================[
 # The Shared Library
 #]============================================================================]
 
diff --git a/arch/x86_64/CMakeLists.txt b/arch/x86_64/CMakeLists.txt
index e9f8d5f..8cb1ca2 100644
--- a/arch/x86_64/CMakeLists.txt
+++ b/arch/x86_64/CMakeLists.txt
@@ -82,6 +82,15 @@ target_sources("_exception" PRIVATE
 )
 
 #[============================================================================[
+# The Context switching Library
+#]============================================================================]
+
+target_sources("_context" PRIVATE
+  "src/context_switching/descriptor_table/gdt_flags.cpp"
+  "src/context_switching/descriptor_table/access_byte.cpp"
+)
+
+#[============================================================================[
 # The Bootable ISO Image
 #]============================================================================]
 
diff --git a/arch/x86_64/include/arch/context_switching/descriptor_table/gdt_flags.hpp b/arch/x86_64/include/arch/context_switching/descriptor_table/gdt_flags.hpp
index e69de29..83a7c06 100644
--- a/arch/x86_64/include/arch/context_switching/descriptor_table/gdt_flags.hpp
+++ b/arch/x86_64/include/arch/context_switching/descriptor_table/gdt_flags.hpp
@@ -0,0 +1,68 @@
+#ifndef TEACHOS_ARCH_X86_64_MEMORY_ALLOCATOR_PHYSICAL_FRAME_HPP
+#define TEACHOS_ARCH_X86_64_MEMORY_ALLOCATOR_PHYSICAL_FRAME_HPP
+
+#include <bitset>
+#include <cstdint>
+
+namespace teachos::arch::context_switching::descriptor_table
+{
+  /**
+   * @brief Defines helper function for all states that the global descriptor flags of a segment descriptor can
+   * have.
+   *
+   * @note See https://docs.oracle.com/cd/E19683-01/816-1386/chapter6-94076/index.html for more information.
+   */
+  struct gdt_flags
+  {
+    /**
+     * @brief Possible set bits in our underlying std::bitset and the meaning when they are set.
+     */
+    enum bitset : uint8_t
+    {
+      GRANULARITY = 1U << 0U,  ///< Indicates the size the Limit value in the segement descriptor is scaled by 1 Byte
+                               ///< blocks if the bit is not set or by 4 KiB blocks if the bit is set.
+      PROTECTED_MODE_SEGMENT_16_OR_32_BIT_SIZE = 1U << 1U,  ///< Descriptor defines either a 16-bit protected mdoe
+                                                            ///< segment if bit is not set or 32-bit if the bit is set.
+      ENABLE_LONG_MODE = 1U << 2U  ///< If set the descriptor defines a 64-bit code segment, when set
+                                   ///< PROTECTED_MODE_SEGMENT_16_OR_32_BIT_SIZE should always be clear. For other types
+                                   ///< of segments bit should not be set.
+    };
+
+    /**
+     * @brief Constructor.
+     *
+     * @param flags Actual value read from the elf section header, which should be converted into a std::bitset, to
+     * allow reading the state of single bits more easily. Only the first 3 bit of the value will actually be converted
+     * into the std::bitset, because the latter 4 bits are not relevant and the 4th bit is reserved.
+     */
+    explicit gdt_flags(uint8_t flags)
+        : flags(flags >> 5U)
+    {
+      // Nothing to do
+    }
+
+    /**
+     * @brief Checks if the given std::bitset is a subset or equivalent to the underlying std::bitset.
+     *
+     * @note Meaning that all bits that are set in the given std::bitset also have to be set in the underlyng
+     * std::bitset. Any additional bits that are set are not relevant.
+     *
+     * @param other Flags that we want to compare against and check if the underlying std::bitset has the same bits set.
+     * @return Whether the given flags are a subset or equivalent with the underlying std::bitset.
+     */
+    auto contains_flags(std::bitset<4U> other) const -> bool;
+
+    /**
+     * @brief Allows to compare the underlying std::bitset of two instances.
+     *
+     * @param other Other instance that we want to compare with.
+     * @return Whether the underlying std::bitset of both types is the same.
+     */
+    auto operator==(gdt_flags const & other) const -> bool = default;
+
+  private:
+    std::bitset<4U> flags;  ///< Underlying bitset used to read the flags from.
+  };
+}  // namespace teachos::arch::context_switching::descriptor_table
+
+#endif  // TEACHOS_ARCH_X86_64_MEMORY_ALLOCATOR_PHYSICAL_FRAME_HPP
diff --git a/arch/x86_64/src/context_switching/descriptor_table/gdt_flags.cpp b/arch/x86_64/src/context_switching/descriptor_table/gdt_flags.cpp
new file mode 100644
index 0000000..8a05956
--- /dev/null
+++ b/arch/x86_64/src/context_switching/descriptor_table/gdt_flags.cpp
@@ -0,0 +1,6 @@
+#include "arch/context_switching/descriptor_table/gdt_flags.hpp"
+
+namespace teachos::arch::context_switching::descriptor_table
+{
+  auto gdt_flags::contains_flags(std::bitset<4U> other) const -> bool { return (flags & other) == other; }
+}  // namespace teachos::arch::context_switching::descriptor_table