From 0a51a5e8bccfdb5e3d99438eb738a5e56ac37590 Mon Sep 17 00:00:00 2001
From: slinky55 <lbmason55@gmail.com>
Date: Tue, 16 Jun 2026 10:04:49 -0400
Subject: [PATCH] added memory mapping functions, created first user process pd

---
 kernel/boot/boot.S |  3 ++-
 kernel/kmain.c     |  5 ++++
 kernel/memory/mm.c | 60 ++++++++++++++++++++++++++++++----------------
 kernel/memory/mm.h |  2 ++
 4 files changed, 49 insertions(+), 21 deletions(-)

diff --git a/kernel/boot/boot.S b/kernel/boot/boot.S
index 21303ab..0e41fab 100644
--- a/kernel/boot/boot.S
+++ b/kernel/boot/boot.S
@@ -52,4 +52,5 @@ page_directory:
 	.long 0x00000083
 	.skip 3068
 	.long 0x00000083
-	.skip 1020
\ No newline at end of file
+	.skip 1016
+	.long (page_directory - 0xC0000000) + 0x03
\ No newline at end of file
diff --git a/kernel/kmain.c b/kernel/kmain.c
index 90ff2f0..284c9fb 100644
--- a/kernel/kmain.c
+++ b/kernel/kmain.c
@@ -21,6 +21,8 @@ void* page = NULL;
 extern char __kernel_start;
 extern char __kernel_end;
 
+void* user_page_directories[10];
+
 void kmain(uint32_t magic, multiboot_info* mbi)  {
   extern print_stream_t vga_print_stream;
   extern print_stream_t* kout;
@@ -68,5 +70,8 @@ void kmain(uint32_t magic, multiboot_info* mbi)  {
   init_page_tables();
   kprintf("Page tables initialized\n");
 
+  user_page_directories[0] = create_user_pd();
+  kprintf("Created first user process page directory @ 0x%x\n", user_page_directories[0]);
+
   while(1);
 }
diff --git a/kernel/memory/mm.c b/kernel/memory/mm.c
index e9c7f41..634d8b9 100644
--- a/kernel/memory/mm.c
+++ b/kernel/memory/mm.c
@@ -17,6 +17,8 @@ extern void disable_pae();
 #define PAGE_TABLES  0xFFC00000
 #define PAGE_DIRECTORY  0xFFFFF000
 
+#define TEMP_MAPPING_VADDR 0xE0000000
+
 #define PAGE_PRESENT  0x1
 #define PAGE_WRITABLE 0x2
 #define PAGE_USER     0x4
@@ -113,28 +115,24 @@ static void p_free_frame(void* addr) {
     mark_free((uint32_t)addr);
 }
 
+// MODIFIES THE ACTIVE PAGE TABLE AT THE PHYSICAL ADDRESS LOADED INTO CR3 VIA RECURSIVE MAPPING
 static void map_page(uint32_t vaddr, uint32_t paddr, uint32_t flags) {
     uint32_t pde_entry = vaddr >> 22;
     uint32_t pte_entry = (vaddr >> 12) & 0x3FF;
+    uint32_t* pd = (uint32_t*)PAGE_DIRECTORY;
+    uint32_t* tablev = (uint32_t*)(PAGE_TABLES + (pde_entry * PAGE_SIZE));
 
-    uint32_t* page_directory = (uint32_t*)PAGE_DIRECTORY;
-    if (page_directory[pde_entry] & PAGE_PRESENT == 0) {
-        uint32_t* new_table = (uint32_t*)p_alloc_frame();
-        page_directory[pde_entry] = (uint32_t)new_table | flags;
-    }
-}
-
-static void* p_alloc(uint32_t size_b, uint32_t vstart) {
-    uint32_t pages = (size_b + PAGE_SIZE - 1) / PAGE_SIZE;
-    
-    for (uint32_t i = 0; i < pages; i++) {
-        uint32_t vaddr = vstart + i * PAGE_SIZE;
-        uint32_t paddr = (uint32_t)p_alloc_frame();
-        
-        map_page(vaddr, paddr, PAGE_PRESENT | PAGE_WRITABLE);
+    if ((pd[pde_entry] & PAGE_PRESENT) == 0) {
+        uint32_t new_table = (uint32_t)p_alloc_frame();
+        pd[pde_entry] = new_table | PAGE_PRESENT | PAGE_WRITABLE;
+        flush_tlb();
+        for (int i = 0; i < 1024; i++) {
+            tablev[i] = 0;
+        }
     }
 
-    return (void*)vstart;
+    tablev[pte_entry] = paddr | flags;
+    flush_tlb();
 }
 
 void init_pmm(void* mmap_base, uint32_t mmap_limit) {
@@ -158,10 +156,32 @@ void init_page_tables() {
     flush_tlb();
 }
 
-void* init_kheap() {
-
-}
-
 uint32_t total_free_memory() {
     return total_available_memory;
+}
+
+void* create_user_pd() {
+    uint32_t pd_address = (uint32_t)p_alloc_frame();
+    if (pd_address == 0) {
+        return 0;
+    }
+
+    map_page(TEMP_MAPPING_VADDR, pd_address, PAGE_PRESENT | PAGE_WRITABLE);
+
+    uint32_t* user_pd = (uint32_t*)TEMP_MAPPING_VADDR;
+    uint32_t* kernel_pd = (uint32_t*)PAGE_DIRECTORY;
+
+    for(int i = 0; i < 1024; i++) {
+        user_pd[i] = 0;
+    }
+
+    user_pd[768] = kernel_pd[768];
+    user_pd[1023] = (uint32_t)pd_address | PAGE_PRESENT | PAGE_WRITABLE;
+
+    uint32_t pde = TEMP_MAPPING_VADDR >> 22;
+    uint32_t pte = (TEMP_MAPPING_VADDR >> 12) & 0x3FF; 
+    uint32_t* kernel_pt = (uint32_t*)(PAGE_TABLES + (pde * PAGE_SIZE));
+    kernel_pt[pte] = 0;
+    flush_tlb();
+    return (void*)pd_address;
 }
\ No newline at end of file
diff --git a/kernel/memory/mm.h b/kernel/memory/mm.h
index 355d50d..a17876a 100644
--- a/kernel/memory/mm.h
+++ b/kernel/memory/mm.h
@@ -13,4 +13,6 @@ void* init_kheap();
 
 uint32_t total_free_memory();
 
+void* create_user_pd();
+
 #endif