Fix next table overwriting old page handle

2 files changed, 9 insertions, 7 deletions

diff --git a/arch/x86_64/include/arch/memory/paging/page_table.hpp b/arch/x86_64/include/arch/memory/paging/page_table.hpp
index 9449ef2..7a15875 100644
--- a/arch/x86_64/include/arch/memory/paging/page_table.hpp
+++ b/arch/x86_64/include/arch/memory/paging/page_table.hpp
@@ -72,7 +72,7 @@ namespace teachos::arch::memory::paging
      *
      * @param table_index Index of this page table in the page table one level lower.
      */
-    auto next_table(std::size_t table_index) -> std::optional<page_table_handle>;
+    auto next_table(std::size_t table_index) const -> std::optional<page_table_handle>;
 
     /**
      * @brief Call next_table and then checks if the table already exists, if it does not it will use the given
@@ -120,8 +120,8 @@ namespace teachos::arch::memory::paging
     auto operator[](std::size_t index) const -> entry const &;
 
     /**
-     * @brief Decrements the page table level enum by one, is defined so we can use it as a replacement for an
-     * int index in a range based for loop.
+     * @brief Pre decrement operator on the page table level enum, is defined so we can use it as a replacement
+     * for an int index in a range based for loop.
      *
      * @note Will halt execution if called with page_table_handle::LEVEL1, because there is no level below. Has to be
      * defined as either a friend function or inline header method, because we define an operator of another type. In
@@ -132,12 +132,13 @@ namespace teachos::arch::memory::paging
      * header file.
      *
      * @param value Value we want to decrement on
-     * @return level New level value decrement by one, meaning the level is also decrement by one Level4 --> Level3, ...
+     * @return New level value decrement by one, meaning the level is also decrement by one Level4 --> Level3, ...
      */
     friend auto operator--(level & value) -> level &;
 
   private:
-    page_table * table;  ///< Handle to underlying page table, can never be null (invariant ensured by constructor)
+    page_table * table;  ///< Handle to underlying page table, can never be null (invariant ensured by
+                         ///< constructor)
     level table_level;   ///< Level page table is currently on, depends on how often next_level was
                          ///< called successfully.
   };
diff --git a/arch/x86_64/src/memory/paging/page_table.cpp b/arch/x86_64/src/memory/paging/page_table.cpp
index a39c235..eb11810 100644
--- a/arch/x86_64/src/memory/paging/page_table.cpp
+++ b/arch/x86_64/src/memory/paging/page_table.cpp
@@ -100,14 +100,15 @@ namespace teachos::arch::memory::paging
 
   auto page_table_handle::is_empty() const -> bool { return table->is_empty(); }
 
-  auto page_table_handle::next_table(std::size_t table_index) -> std::optional<page_table_handle>
+  auto page_table_handle::next_table(std::size_t table_index) const -> std::optional<page_table_handle>
   {
     exception_handling::assert(table_level != page_table_handle::LEVEL1,
                                "[Page Table] Attempted to call next_table on level 1 page table");
     auto const next_table = table->next_table(table_index);
     if (next_table.has_value())
     {
-      return page_table_handle{next_table.value(), --table_level};
+      auto const new_level = static_cast<page_table_handle::level>(table_level - 1);
+      return page_table_handle{next_table.value(), new_level};
     }
     return std::nullopt;
   }