From b9d445bf92725d79269becf978059e040519c00a Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@ost.ch>
Date: Wed, 10 Dec 2025 16:51:44 +0100
Subject: x86_64/memory: implement simple kernel remapper

---
 arch/x86_64/src/memory/kernel_mapper.cpp | 107 +++++++++++++++++++++++++++++++
 1 file changed, 107 insertions(+)
 create mode 100644 arch/x86_64/src/memory/kernel_mapper.cpp

(limited to 'arch/x86_64/src/memory/kernel_mapper.cpp')

diff --git a/arch/x86_64/src/memory/kernel_mapper.cpp b/arch/x86_64/src/memory/kernel_mapper.cpp
new file mode 100644
index 0000000..b1d12a4
--- /dev/null
+++ b/arch/x86_64/src/memory/kernel_mapper.cpp
@@ -0,0 +1,107 @@
+#include "x86_64/memory/kernel_mapper.hpp"
+
+#include "kapi/cio.hpp"
+#include "kapi/memory.hpp"
+#include "kapi/system.hpp"
+
+#include "x86_64/boot/ld.hpp"
+#include "x86_64/memory/page_table.hpp"
+#include "x86_64/memory/paging_root.hpp"
+
+#include <elf/format.hpp>
+#include <elf/section_header.hpp>
+
+#include <algorithm>
+#include <ranges>
+
+namespace teachos::memory::x86_64
+{
+
+  inline namespace
+  {
+    using namespace std::string_view_literals;
+
+    constexpr auto static ignored_section_prefixes = std::array{
+      ".boot_"sv,
+    };
+
+    constexpr auto static user_accessible_prefixes = std::array{
+      ".user"sv,
+      ".stl"sv,
+    };
+
+  }  // namespace
+
+  kernel_mapper::kernel_mapper(frame_allocator & allocator, multiboot2::information_view const * mbi)
+      : m_allocator{&allocator}
+      , m_mbi(std::move(mbi))
+      , m_kernel_load_base{std::bit_cast<std::uintptr_t>(&boot::x86_64::TEACHOS_VMA)}
+  {}
+
+  auto kernel_mapper::remap_kernel() -> void
+  {
+    auto elf_information = m_mbi->maybe_elf_symbols<elf::format::elf64>();
+    if (!elf_information)
+    {
+      system::panic("[x86_64:MEM] ELF section information is not available.");
+    }
+
+    auto sections = *elf_information;
+    auto allocated_sections =
+        std::views::all(sections) | std::views::filter(&elf::section_header<elf::format::elf64>::allocated) |
+        std::views::filter([&](auto const & section) -> auto {
+          auto name = sections.name(section);
+          return !std::ranges::any_of(ignored_section_prefixes,
+                                      [&](auto const & prefix) -> auto { return name.starts_with(prefix); });
+        });
+
+    if (allocated_sections.empty())
+    {
+      system::panic("[x86_64:MEM] No allocated ELF sections were found.");
+    }
+
+    std::ranges::for_each(allocated_sections,
+                          [&](auto const & section) -> auto { map_section(section, sections.name(section)); });
+  }
+
+  auto kernel_mapper::map_section(section_header_type const & section, std::string_view name) -> void
+  {
+    cio::print("[x86_64:MEM] mapping ");
+    cio::println(name);
+
+    auto number_of_pages = (section.size + (PLATFORM_PAGE_SIZE - 1)) / PLATFORM_PAGE_SIZE;
+
+    auto linear_start_address = linear_address{section.virtual_load_address};
+    auto physical_start_address = physical_address{section.virtual_load_address & ~m_kernel_load_base};
+
+    auto first_page = page::containing(linear_start_address);
+    auto first_frame = frame::containing(physical_start_address);
+
+    auto page_flags = page_table::entry::flags::empty;
+
+    if (section.writable())
+    {
+      page_flags |= page_table::entry::flags::writable;
+    }
+
+    if (!section.executable())
+    {
+      page_flags |= page_table::entry::flags::no_execute;
+    }
+
+    auto is_prefix_of_name = [=](auto prefix) -> bool {
+      return name.starts_with(prefix);
+    };
+
+    if (std::ranges::any_of(user_accessible_prefixes, is_prefix_of_name))
+    {
+      page_flags |= page_table::entry::flags::user_accessible;
+    }
+
+    for (auto i = 0uz; i < number_of_pages; ++i)
+    {
+      paging_root::get().map(page{first_page.number() + i}, frame{first_frame.number() + i}, page_flags, *m_allocator);
+    }
+  }
+
+}  // namespace teachos::memory::x86_64
\ No newline at end of file
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