From ddf3cfff681ec4af542a1d4ee32736259f7e2a19 Mon Sep 17 00:00:00 2001
From: 0x35c <unai64@orange.fr>
Date: Wed, 18 Sep 2024 17:14:06 +0200
Subject: [PATCH] feature: enable paging and load page directory

---
 headers/memory.h     | 29 +++++++++++++++++++++++++++++
 src/kernel.c         |  6 ++----
 src/memory/load_pd.s | 12 ++++++++++++
 src/memory/memory.c  | 18 ++++++++++++++++++
 src/memory/paging.s  | 13 +++++++++++++
 5 files changed, 74 insertions(+), 4 deletions(-)
 create mode 100644 headers/memory.h
 create mode 100644 src/memory/load_pd.s
 create mode 100644 src/memory/memory.c
 create mode 100644 src/memory/paging.s

diff --git a/headers/memory.h b/headers/memory.h
new file mode 100644
index 0000000..ab5c9e5
--- /dev/null
+++ b/headers/memory.h
@@ -0,0 +1,29 @@
+#pragma once
+
+#include <stdint.h>
+
+#define NOT_PRESENT (1 << 0)
+#define RW          (1 << 1)
+#define SUPERVISOR  (0 << 2)
+#define INIT_FLAGS  (NOT_PRESENT | RW | SUPERVISOR)
+
+struct page_directory_entry {
+	uint32_t present : 1;
+	uint32_t rw : 1;
+	uint32_t user : 1;
+	uint32_t page_size : 1;
+	uint32_t unused : 8;
+	uint32_t frame : 20;
+};
+
+struct page_table_entry {
+	uint32_t present : 1;
+	uint32_t rw : 1;
+	uint32_t user : 1;
+	uint32_t accessed : 1;
+	uint32_t dirty : 1;
+	uint32_t unused : 7;
+	uint32_t frame : 20;
+};
+
+void init_memory(void);
diff --git a/src/kernel.c b/src/kernel.c
index 046d342..a94583e 100644
--- a/src/kernel.c
+++ b/src/kernel.c
@@ -1,8 +1,7 @@
 #include "gdt.h"
+#include "memory.h"
 #include "shell.h"
 #include "terminal.h"
-/* #include "power.h" */
-#include "gdt.h"
 
 #include <stdbool.h>
 #include <stddef.h>
@@ -21,9 +20,8 @@
 
 void kernel_main(void)
 {
-	/* Initialize terminal interface */
 	terminal_initialize();
-
 	init_gdt();
+	init_memory();
 	shell_init();
 }
diff --git a/src/memory/load_pd.s b/src/memory/load_pd.s
new file mode 100644
index 0000000..bffd31d
--- /dev/null
+++ b/src/memory/load_pd.s
@@ -0,0 +1,12 @@
+.intel_syntax noprefix
+
+.text
+.global load_page_directory
+load_page_directory:
+push ebp
+mov ebp, esp
+mov eax, [esp + 8]
+mov cr3, eax
+mov esp, ebp
+pop ebp
+ret
diff --git a/src/memory/memory.c b/src/memory/memory.c
new file mode 100644
index 0000000..a0e5c20
--- /dev/null
+++ b/src/memory/memory.c
@@ -0,0 +1,18 @@
+#include "memory.h"
+#include "string.h"
+
+extern void load_page_directory(uint32_t *);
+extern void enable_paging(void);
+
+uint32_t page_directory_entries[1024] __attribute__((aligned(4096)));
+uint32_t page_table_entries[1024] __attribute__((aligned(4096)));
+
+void init_memory(void)
+{
+	memset(page_directory_entries, INIT_FLAGS, 1024);
+	for (int i = 0; i < 1024; i++)
+		page_table_entries[i] = (i << 12) | INIT_FLAGS;
+	page_directory_entries[0] = (uint32_t)page_table_entries | INIT_FLAGS;
+	load_page_directory(page_directory_entries);
+	enable_paging();
+}
diff --git a/src/memory/paging.s b/src/memory/paging.s
new file mode 100644
index 0000000..10d62d3
--- /dev/null
+++ b/src/memory/paging.s
@@ -0,0 +1,13 @@
+.intel_syntax noprefix
+
+.text
+.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