A update

lib/mm/pmm.c

@@ -0,0 +1,79 @@
+#include <stddef.h>
+
+#include <mm/pmm.h>
+
+#define PAGE_SIZE 4096
+#define BITMAP_SIZE (1024 * 1024) /* Supports up to 4GB RAM (1 bit per page) */
+
+static uint8_t bitmap[BITMAP_SIZE / 8];
+static uint32_t total_pages;
+static uint32_t used_pages = 0;
+
+static inline void set_bit(uint32_t idx)
+{
+  bitmap[idx / 8] |= (1 << (idx % 8));
+}
+
+static inline void clear_bit(uint32_t idx)
+{
+  bitmap[idx / 8] &= ~(1 << (idx % 8));
+}
+
+static inline int test_bit(uint32_t idx)
+{
+  return (bitmap[idx / 8] >> (idx % 8)) & 1;
+}
+
+void pmm_init(multiboot_info_t* mb_info)
+{
+  total_pages = 0x100000; /* 4GB / 4KB = 1M pages */
+  for (uint32_t i = 0; i < total_pages / 8; i++)
+  {
+      bitmap[i] = 0xFF; /* Mark all as used */
+  }
+
+  multiboot_memory_map_t* mmap = (multiboot_memory_map_t*) mb_info->mmap_addr;
+  while ((uint32_t)mmap < mb_info->mmap_addr + mb_info->mmap_length)
+  {
+    if (mmap->type == 1) /* Usable */
+    {
+      uint64_t base = mmap->addr;
+      uint64_t len = mmap->len;
+      for (uint64_t addr = base; addr < base + len; addr += PAGE_SIZE)
+      {
+        if (addr >= 0x210000) /* Skip first 2.1MB, or ≈ 2.06MiB */
+        {
+          uint32_t idx = addr / PAGE_SIZE;
+          
+          if (idx >= total_pages)
+          {
+            continue; /* skip entries above 4GB */
+          }
+          
+          clear_bit(idx);
+          used_pages--;
+        }
+      }
+    }
+    mmap = (multiboot_memory_map_t*)((uint32_t)mmap + mmap->size + sizeof(mmap->size));
+  }
+}
+
+void* alloc_page(void) {
+  for (uint32_t i = 0; i < total_pages; i++)
+  {
+    if (!test_bit(i))
+    {
+      set_bit(i);
+      used_pages++;
+      return (void*)(i * PAGE_SIZE);
+    }
+  }
+  return NULL; /* Out of memory */
+}
+
+void free_page(void* ptr)
+{
+  uint32_t idx = (uint32_t)ptr / PAGE_SIZE;
+  clear_bit(idx);
+}