syscalls: start adding fork syscall, not done yet

src/mm/paging.c

@@ -188,4 +188,63 @@ void destroy_page_dir(uint32_t* page_dir_virt) {
     // We need its physical address to pass to the physical memory manager.
     debug_log("freeing PD page %X\n", virt_to_phys(page_dir_virt));
     free_page((void*)virt_to_phys(page_dir_virt));
+}
+
+uint32_t* copy_page_dir(uint32_t* page_dir_virt)
+{
+    if(page_dir_virt == NULL)
+        return 0;
+    
+    uint32_t* new_pagedir = create_page_dir();
+    
+    for(int i = 0; i < 768; i++)
+    {
+        uint32_t pde = page_dir_virt[i];
+
+        if(pde & PAGE_PRESENT)
+        {
+            debug_log("PDE %X present\n", pde);
+            uint32_t* new_page_table = (uint32_t*)alloc_page();
+            if(new_page_table == NULL) {
+                return NULL;
+            }
+            
+            // Get original page table (physical address from PDE)
+            uint32_t* orig_page_table = (uint32_t*)phys_to_virt(pde & ~0xFFF);
+
+            for(int j = 0; j < 1024; j++)
+            {
+                uint32_t pte = orig_page_table[j];
+                if(pte & PAGE_PRESENT)
+                {
+                    void* new_phys_page = alloc_page();
+                    if(!new_phys_page)
+                    {
+                        return NULL;
+                    }
+
+                    void* orig_phys_page = (void*)(pte & ~0xFFF);
+
+                    debug_log("copying %X to %X...", orig_phys_page, new_phys_page);
+                    memcpy(new_phys_page, orig_phys_page, PAGE_SIZE);
+                    debug_log("done\n");
+                    new_page_table[j] = (uint32_t)new_phys_page | (pte & 0xFFF);
+                }
+                else
+                {
+                    new_page_table[j] = pte;
+                }
+            }
+            
+            
+            // Set the new PDE in the child's page directory
+            new_pagedir[i] = (uint32_t)virt_to_phys(new_page_table) | (pde & 0xFFF);
+        }
+        else
+        {
+            new_pagedir[i] = pde;
+        }
+    }
+    debug_log("ENDENDENDEND\n");
+    return new_pagedir;
 }