Convert elf section flags to entry flags

3 files changed, 43 insertions, 3 deletions

diff --git a/arch/x86_64/include/arch/memory/paging/kernel_mapper.hpp b/arch/x86_64/include/arch/memory/paging/kernel_mapper.hpp
index f30ca24..54ec682 100644
--- a/arch/x86_64/include/arch/memory/paging/kernel_mapper.hpp
+++ b/arch/x86_64/include/arch/memory/paging/kernel_mapper.hpp
@@ -116,11 +116,11 @@ namespace teachos::arch::memory::paging
         allocator::physical_frame_iterator const begin{start_frame};
         allocator::physical_frame_iterator const end{end_frame};
         frame_container frames{begin, end};
+        entry entry{section.flags};
 
         for (auto const & frame : frames)
         {
-          // TODO: Use actual elf section flags, convert from one to the other flag type.
-          active_table.identity_map(allocator, frame, entry::WRITABLE);
+          active_table.identity_map(allocator, frame, entry.get_flags());
         }
       }
     }
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 5959801..ab9659d 100644
--- a/arch/x86_64/include/arch/memory/paging/page_entry.hpp
+++ b/arch/x86_64/include/arch/memory/paging/page_entry.hpp
@@ -2,6 +2,7 @@
 #define TEACHOS_ARCH_X86_64_MEMORY_PAGING_PAGE_ENTRY_HPP
 
 #include "arch/memory/allocator/physical_frame.hpp"
+#include "arch/memory/multiboot/elf_symbols_section.hpp"
 
 #include <bitset>
 #include <optional>
@@ -48,6 +49,18 @@ namespace teachos::arch::memory::paging
     explicit entry(uint64_t flags);
 
     /**
+     * @brief Converts the given elf section flags into the corresponding correct entry flags.
+     *
+     * @note Enables us to set the correct flags on a entry depending on which elf section it is contained in. For
+     * example entries of .text sections should be executable and read only or entries of .data sections should be
+     * writable but not executable.
+     *
+     * @param elf_flags Elf section flags we want to convert into entry flags.
+     * @return Entry that has the corresponding bit flags set.
+     */
+    explicit entry(multiboot::elf_section_flags elf_flags);
+
+    /**
      * @brief Whether the current page is unused, meaning the underlying std::bitset is 0.
      *
      * @return Current page is in memory.
@@ -86,6 +99,13 @@ namespace teachos::arch::memory::paging
      */
     auto contains_flags(std::bitset<64U> other) const -> bool;
 
+    /**
+     * @brief Extracts only the flags from the underlying entry and ignores all bits that contain the physical address.
+     *
+     * @return Extracted entry flags, without the physical address.
+     */
+    auto get_flags() -> std::bitset<64U>;
+
   private:
     std::bitset<64U> flags;  ///< Underlying bitset used to read the flags from. Bits 9 - 11 and 52 - 62 can be
                              ///< freely used for additional flags by the operating system.
diff --git a/arch/x86_64/src/memory/paging/page_entry.cpp b/arch/x86_64/src/memory/paging/page_entry.cpp
index 23c700f..5c4bc67 100644
--- a/arch/x86_64/src/memory/paging/page_entry.cpp
+++ b/arch/x86_64/src/memory/paging/page_entry.cpp
@@ -7,7 +7,8 @@ namespace teachos::arch::memory::paging
   namespace
   {
     std::size_t constexpr PHYSICAL_ADDRESS_MASK = 0x000fffff'fffff000;
-  }
+    std::size_t constexpr ENTRY_FLAGS_MASK = 0xfff00000'00000fff;
+  }  // namespace
 
   entry::entry(uint64_t flags)
       : flags(flags)
@@ -15,6 +16,23 @@ namespace teachos::arch::memory::paging
     // Nothing to do.
   }
 
+  entry::entry(multiboot::elf_section_flags elf_flags)
+  {
+    if (elf_flags.contains_flags(multiboot::elf_section_flags::OCCUPIES_MEMORY))
+    {
+      flags = flags.to_ulong() | entry::PRESENT;
+    }
+    if (elf_flags.contains_flags(multiboot::elf_section_flags::WRITABLE))
+    {
+      flags = flags.to_ulong() | entry::WRITABLE;
+    }
+    if (!elf_flags.contains_flags(multiboot::elf_section_flags::EXECUTABLE_CODE))
+    {
+      // TODO: Ensure to set the NXE bit, if we don't using this entry flag causes crashes
+      // flags = flags.to_ulong() | entry::EXECUTING_CODE_FORBIDDEN;
+    }
+  }
+
   auto entry::is_unused() const -> bool { return flags == 0U; }
 
   auto entry::set_unused() -> void { flags = 0U; }
@@ -37,4 +55,6 @@ namespace teachos::arch::memory::paging
                                "[Paging Entry] Start address is not aligned with page");
     flags = frame.start_address() | additional_flags.to_ulong();
   }
+
+  auto entry::get_flags() -> std::bitset<64U> { return flags.to_ulong() & ENTRY_FLAGS_MASK; }
 }  // namespace teachos::arch::memory::paging