[feat] Simple Filesystem

kernel/memory/heap.cpp

@@ -112,7 +112,7 @@ void* kmalloc(UINTN size) {
                 split->size = block_sz - alloc_size;
                 // Insert split into free list
                 split->next = block->next;
-                block->size = alloc_size;
+                block->size = alloc_size | 1;
                 *prev = split;
             } else {
                 // Use the whole block

kernel/memory/pmm.cpp

@@ -133,6 +133,15 @@ EFI_STATUS pmm_init() {
         bitmap_set((UINTN)p);
     }
 
+    // Reserve low memory (first 4 MB) — UEFI firmware may use it during BS calls
+    UINT64 low_reserve_pages = 0x400;
+    for (UINT64 p = 0; p < low_reserve_pages && p < g_pmm.total_pages; p++) {
+        if (!bitmap_test((UINTN)p)) {
+            bitmap_set((UINTN)p);
+            g_pmm.free_pages--;
+        }
+    }
+
     // Build free list by linking free pages
     g_pmm.free_list_head = NULL;
     void* prev = NULL;
@@ -145,6 +154,7 @@ EFI_STATUS pmm_init() {
 
         for (UINT64 p = start_page; p < end_page; p++) {
             if (p >= bm_start_page && p < bm_end_page) continue;
+            if (p < low_reserve_pages) continue;
             void* page = (void*)(UINTN)(p * PAGE_SIZE);
             if (prev) {
                 *(void**)prev = page;