From e284d574ed9237a215d994861cc502452fec11ce Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@ost.ch>
Date: Fri, 13 Mar 2026 22:28:50 +0100
Subject: kernel/memory: implement basic bitmap allocator

---
 kernel/kapi/memory.cpp | 56 +++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 53 insertions(+), 3 deletions(-)

(limited to 'kernel/kapi')

diff --git a/kernel/kapi/memory.cpp b/kernel/kapi/memory.cpp
index 7c9b1da..1699cd3 100644
--- a/kernel/kapi/memory.cpp
+++ b/kernel/kapi/memory.cpp
@@ -2,8 +2,17 @@
 
 #include "kapi/system.hpp"
 
+#include "kernel/memory/bitmap_allocator.hpp"
+
+#include <kstd/print>
+
+#include <algorithm>
+#include <bit>
 #include <cstddef>
+#include <cstdint>
 #include <optional>
+#include <ranges>
+#include <span>
 #include <utility>
 
 namespace kapi::memory
@@ -20,6 +29,11 @@ namespace kapi::memory
         system::panic("Tried to allocate frames without an active allocator.");
       }
 
+      auto mark_used(frame) -> void override
+      {
+        system::panic("Tried to mark frame as used without an active allocator.");
+      }
+
       auto release_many(std::pair<frame, std::size_t>) -> void override
       {
         system::panic("Tried to release frames without an active allocator.");
@@ -48,11 +62,17 @@ namespace kapi::memory
 
     constinit bad_frame_allocator bad_frame_allocator::instance{};
     constinit bad_page_mapper bad_page_mapper::instance{};
+    auto constinit allocator = std::optional<kernel::memory::bitmap_frame_allocator>{};
   }  // namespace
 
   constinit auto static active_frame_allocator = static_cast<frame_allocator *>(&bad_frame_allocator::instance);
   constinit auto static active_page_mapper = static_cast<page_mapper *>(&bad_page_mapper::instance);
 
+  auto get_frame_allocator() -> frame_allocator &
+  {
+    return *active_frame_allocator;
+  }
+
   auto set_frame_allocator(frame_allocator & allocator) -> std::optional<frame_allocator *>
   {
     if (&allocator == active_frame_allocator)
@@ -73,12 +93,12 @@ namespace kapi::memory
 
   auto allocate_frame() -> std::optional<frame>
   {
-    return active_frame_allocator->allocate();
+    return get_frame_allocator().allocate();
   }
 
   auto allocate_many_frames(std::size_t count) -> std::optional<std::pair<frame, std::size_t>>
   {
-    return active_frame_allocator->allocate_many(count);
+    return get_frame_allocator().allocate_many(count);
   }
 
   auto map(page page, frame frame) -> std::byte *
@@ -91,4 +111,34 @@ namespace kapi::memory
     return active_page_mapper->unmap(page);
   }
 
-}  // namespace kapi::memory
\ No newline at end of file
+  auto init_pmm(std::size_t frame_count, void (&handoff_handler)(frame_allocator &)) -> void
+  {
+    auto const bitmap_bytes = (frame_count + 7uz) / 8uz;
+    auto const bitmap_pages = (bitmap_bytes + page::size - 1uz) / page::size;
+
+    auto const bitmap_frames = allocate_many_frames(bitmap_pages);
+    if (!bitmap_frames)
+    {
+      system::panic("[OS:MEM] Not enough memory for bitmap allocator!");
+    }
+
+    auto const base_address = 0xffff'c000'0000'0000uz;
+    auto const flags = page_mapper::flags::writable | page_mapper::flags::supervisor_only;
+
+    std::ranges::for_each(std::views::iota(0uz, bitmap_pages), [&](auto index) {
+      auto page = page::containing(linear_address{base_address + index * page::size});
+      auto frame = memory::frame(bitmap_frames->first.number() + index);
+      active_page_mapper->map(page, frame, flags);
+    });
+
+    auto bitmap_ptr = std::bit_cast<std::uint64_t *>(base_address);
+    auto bitmap = std::span{bitmap_ptr, (bitmap_bytes + sizeof(std::uint64_t) - 1uz) / sizeof(std::uint64_t)};
+
+    allocator.emplace(bitmap, frame_count);
+
+    handoff_handler(allocator.value());
+    set_frame_allocator(allocator.value());
+    kstd::println("[OS:MEM] Physical memory manager initialized.");
+  }
+
+}  // namespace kapi::memory
-- 
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