From 920d0b01e1b6623cb3a1b48f6cd4f9a0f3c8a06a Mon Sep 17 00:00:00 2001
From: Nathan Singer <nathan.r.singer@gmx.com>
Date: Mon, 9 Jun 2025 21:01:17 -0400
Subject: [PATCH] paging is now enabled with __shaky__ code

---
 TODO.md                         |  3 ++
 kernel/arch/io/io.s             |  2 +-
 kernel/arch/paging.c            |  6 ----
 kernel/arch/paging/paging.c     | 55 +++++++++++++++++++++++++++++++++
 kernel/arch/paging/paging_src.s | 20 ++++++++++++
 kernel/include/kernel/paging.h  | 17 ++++++++--
 kernel/kmain.c                  |  4 ++-
 7 files changed, 97 insertions(+), 10 deletions(-)
 delete mode 100644 kernel/arch/paging.c
 create mode 100644 kernel/arch/paging/paging.c
 create mode 100644 kernel/arch/paging/paging_src.s

diff --git a/TODO.md b/TODO.md
index a262528..a658665 100644
--- a/TODO.md
+++ b/TODO.md
@@ -5,6 +5,9 @@
     (https://wiki.osdev.org/Troubleshooting#Showing_the_stack_content)
     lets implmeent some better testing functions aswell
 - Paging & virtual memory
+    - Get GRUB to show memory map - DONE
+    - Write a page allocator - WIP
+    - Setup paging
     - Setup higher half kernel
 - Heap allocator (malloc)
     - after this, implment some data structures? cleanup queue?
diff --git a/kernel/arch/io/io.s b/kernel/arch/io/io.s
index 7e2ae7b..c94152e 100644
--- a/kernel/arch/io/io.s
+++ b/kernel/arch/io/io.s
@@ -10,7 +10,7 @@ outb:
 	ret			; return to the calling function
 
 
-global outb_16
+global outb_16 ; TODO these are probably wrong, eh, the stack might need more bcs the variables are bigger? im not sure
 outb_16:
 	mov ax, [esp + 8]
 	mov dx, [esp + 4]
diff --git a/kernel/arch/paging.c b/kernel/arch/paging.c
deleted file mode 100644
index 6ba6414..0000000
--- a/kernel/arch/paging.c
+++ /dev/null
@@ -1,6 +0,0 @@
-#include <stdint.h>
-
-extern uint32_t endkernel; // found in link.ld
-
-
-
diff --git a/kernel/arch/paging/paging.c b/kernel/arch/paging/paging.c
new file mode 100644
index 0000000..4ceafb1
--- /dev/null
+++ b/kernel/arch/paging/paging.c
@@ -0,0 +1,55 @@
+#include <stdint.h>
+
+#include <stdio.h>
+
+#include <kernel/paging.h>
+
+//extern uint32_t endkernel; // found in link.ld
+
+/**
+ * The page table must be page aligned (aligned at 4KiB)
+ *
+ *
+ * This is a temporary solution, as we want a page frame allocator, to properly get page frames.. but this works for now
+ */
+uint32_t page_directory[PAGE_DIRECTORY_ENTRIES] __attribute__((aligned(4096)));
+
+uint32_t first_page_table[PAGE_TABLE_ENTRIES] __attribute__((aligned(4096)));
+
+void setup_page_table(void)
+{
+	uint32_t i;
+	for (i = 0; i < PAGE_TABLE_ENTRIES; i++) {
+		first_page_table[i] = (i * 0x1000) | 3; // supervisor, r/w, present
+	}
+	puts("test");
+}
+
+void setup_page_dir(void)
+{
+	setup_page_table();
+	/**
+	 * Now that we have a page directory, we need to blank it.
+	 *
+	 * The page directory should have exactly 1024 entries. We will set each entry to not present, so that the if the
+	 * MMU looks for that page table, it will see that it is not there yet.
+	 */
+	int i;
+	for (i = 0; i < PAGE_DIRECTORY_ENTRIES; i++) {
+		// This sets the following flags to the pages:
+		// 	Supervisor: Only kernel-mode can access them
+		// 	Write Enabled: It can be both read from and written to
+		// 	Not Present: The page table is not present
+		page_directory[i] = 0x00000002;
+	}
+
+	page_directory[0] = ((uint32_t) first_page_table) | 3;
+}
+
+void setup_paging(void)
+{
+	setup_page_dir();
+
+	load_page_directory(page_directory);
+	enable_paging();
+}
diff --git a/kernel/arch/paging/paging_src.s b/kernel/arch/paging/paging_src.s
new file mode 100644
index 0000000..36fc876
--- /dev/null
+++ b/kernel/arch/paging/paging_src.s
@@ -0,0 +1,20 @@
+global load_page_directory
+load_page_directory:
+	push ebp
+	mov esp, ebp
+	mov eax, [esp + 4]
+	mov cr3, eax
+	mov esp, ebp
+	pop ebp
+	ret
+
+global enable_paging
+enable_paging:
+	push ebp
+	mov ebp, esp
+	mov eax, cr0
+	or eax, 0x80000000
+	mov cr0, eax
+	mov esp, ebp
+	pop ebp
+	ret
diff --git a/kernel/include/kernel/paging.h b/kernel/include/kernel/paging.h
index 75a5e30..d41c280 100644
--- a/kernel/include/kernel/paging.h
+++ b/kernel/include/kernel/paging.h
@@ -1,3 +1,16 @@
-typedef struct {
+#include <stdint.h>
 
-} pageframe_t;
+#ifndef ARCH_PAGING_H
+#define ARCH_PAGING_H
+
+#define PAGE_TABLE_ENTRIES 1024
+#define PAGE_DIRECTORY_ENTRIES 1024
+
+void load_page_directory(uint32_t*);
+
+void enable_paging();
+
+
+void setup_paging(void);
+
+#endif
diff --git a/kernel/kmain.c b/kernel/kmain.c
index 45ad6a1..820ecb4 100644
--- a/kernel/kmain.c
+++ b/kernel/kmain.c
@@ -5,12 +5,12 @@
 #include <kernel/_kernel.h>
 #include <kernel/tty.h>
 #include <kernel/serial.h>
+#include <kernel/paging.h>
 #include <kernel/x86/gdt.h>
 #include <kernel/x86/idt.h>
 #include <kernel/x86/io.h>
 #include <kernel/x86/keyb.h>
 #include <kernel/x86/pit.h>
-
 #include <kernel/x86/pci.h>
 
 #include "multiboot.h"
@@ -76,6 +76,8 @@ void _main(multiboot_info_t* mbd, uint32_t magic)
 	serial_initialize();
 #endif
 
+	setup_paging();
+
 	init_kb();
 
 	init_pit(0x36, PIT_CHANNEL_0, 0);