Enable paging.

CMakeLists.txt

@@ -49,6 +49,7 @@ if(${CMAKE_SYSTEM_PROCESSOR} MATCHES "i.86")
 		${SRCS}
 		src/kernel/arch/x86/gdt.s
 		src/kernel/arch/x86/gdt.c
+		src/kernel/arch/x86/paging.c
 		src/kernel/arch/x86/tty.c)
 	set(CMAKE_EXE_LINKER_FLAGS
 		"-T ${CMAKE_CURRENT_SOURCE_DIR}/src/kernel/arch/x86/linker.ld -ffreestanding -nostdlib")

src/kernel/arch/x86/boot.s

@@ -67,6 +67,15 @@ _start:
 	movw $0x28, %ax
 	ltr %ax
 
+	# paging
+	call setup_paging  # will return pointer to page directory
+	# load page directory
+	movl %eax, %cr3
+	# enable the paging
+	movl %cr0, %eax
+	orl $0x80000000, %eax
+	movl %eax, %cr0
+
 boot_kernel:
 	# enter high-level kernel (C)
 	call kernel_main

src/kernel/arch/x86/paging.c

@@ -0,0 +1,47 @@
+/*
+ * Copyright (C) 2018  Ortega Froysa, Nicolás <nortega@themusicinnoise.net>
+ * Author: Ortega Froysa, Nicolás <nortega@themusicinnoise.net>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdint.h>
+#include <stddef.h>
+
+uint32_t page_dir[1024] __attribute__((aligned(4096)));
+uint32_t page_table[1024] __attribute__((aligned(4096)));
+
+uint32_t *setup_paging() {
+	/*
+	 * set all pages to:
+	 *  - supervisor: only kernel-mode can access
+	 *  - write enabled: can be read and written
+	 *  - not present: the page table is not present
+	 */
+	for(size_t i = 0; i < 1024; ++i)
+		page_dir[i] = 0x00000002;
+
+	/*
+	 * fill the 1024 entries of the table with the flags
+	 * supervisor, write enabled, and PRESENT.
+	 */
+	for(size_t i = 0; i < 1024; ++i)
+		page_table[i] = (i * 0x1000) | 3;
+
+	// put page table in first directory and enable the present
+	// flag
+	page_dir[0] = ((uint32_t) page_table) | 3;
+
+	return page_dir;
+}