From f4ab51df7f9ed783dbcfbecffc0a9d919c501135 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Matteo=20Gm=C3=BCr?= <matteo.gmuer1@ost.ch>
Date: Sat, 26 Oct 2024 11:44:12 +0000
Subject: Write P3 table into P4 table at index 0

---
 arch/x86_64/include/arch/memory/paging/page_entry.hpp | 8 ++++++++
 arch/x86_64/src/memory/paging/page_entry.cpp          | 6 ++++++
 arch/x86_64/src/memory/paging/page_table.cpp          | 2 ++
 3 files changed, 16 insertions(+)

(limited to 'arch')

diff --git a/arch/x86_64/include/arch/memory/paging/page_entry.hpp b/arch/x86_64/include/arch/memory/paging/page_entry.hpp
index 9ca5469..ba972d6 100644
--- a/arch/x86_64/include/arch/memory/paging/page_entry.hpp
+++ b/arch/x86_64/include/arch/memory/paging/page_entry.hpp
@@ -34,6 +34,14 @@ namespace teachos::arch::memory::paging
           1UL << 63UL,  ///< Page is forbidden from executing code (NXE bit in the EFER register has to be set)
     };
 
+    /**
+     * @brief Creates a new entry object from a 64bit address. Should follow the scheme where bit index 12 - 51 are the
+     * actual address and the other bits are flags.
+     *
+     * @param flags Flags that will be passed to underlying std::bitset.
+     */
+    explicit entry(uint64_t flags);
+
     /**
      * @brief Whether the current page is unused, meaning the underlying std::bitset is 0.
      *
diff --git a/arch/x86_64/src/memory/paging/page_entry.cpp b/arch/x86_64/src/memory/paging/page_entry.cpp
index 5d597ab..09d048b 100644
--- a/arch/x86_64/src/memory/paging/page_entry.cpp
+++ b/arch/x86_64/src/memory/paging/page_entry.cpp
@@ -4,6 +4,12 @@
 
 namespace teachos::arch::memory::paging
 {
+  entry::entry(uint64_t flags)
+      : flags(flags)
+  {
+    // Nothing to do.
+  }
+
   auto entry::is_unused() const -> bool { return flags == 0U; }
 
   auto entry::set_unused() -> void { flags = 0U; }
diff --git a/arch/x86_64/src/memory/paging/page_table.cpp b/arch/x86_64/src/memory/paging/page_table.cpp
index c0f199a..4747e0b 100644
--- a/arch/x86_64/src/memory/paging/page_table.cpp
+++ b/arch/x86_64/src/memory/paging/page_table.cpp
@@ -123,6 +123,8 @@ namespace teachos::arch::memory::paging
         std::construct_at(reinterpret_cast<page_table *>(&_end_of_image + offset));
       }
     }
+    size_t const flags = reinterpret_cast<size_t>(level3_page_table);
+    this->operator[](0U) = entry{flags};
   }
 
   auto page_table_handle::zero_entries() -> void { handle->zero_entries(); }
-- 
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