Enable paging first before loading GDT.

It's assembly code, so no need to name it.

CMakeLists.txt

@@ -35,6 +35,17 @@ set(CMAKE_ASM_FLAGS "")
 set(CMAKE_ASM_FLAGS_DEBUG "-g")
 set(CMAKE_ASM_FLAGS_RELEASE "")
 
+set(CMAKE_EXE_LINKER_FLAGS "-ffreestanding -nostdlib")
+
+# perform data type checks
+include(CheckTypeSize)
+if(64BIT)
+	check_type_size("uint64_t" UINT64_T)
+endif()
+check_type_size("uint32_t" UINT32_T)
+check_type_size("uint16_t" UINT16_T)
+check_type_size("uint8_t" UINT8_T)
+
 include_directories(
 	"src/")
 
@@ -49,9 +60,10 @@ 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")
+		"-T ${CMAKE_CURRENT_SOURCE_DIR}/src/kernel/arch/x86/linker.ld ${CMAKE_EXE_LINKER_FLAGS}")
 	include_directories(
 		"src/kernel/arch/x86/")
 endif()

src/kernel/arch/x86/boot.s

@@ -61,8 +61,20 @@ _start:
 	mov $stack_top, %esp
 	mov %esp, %ebp
 
+	# 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
+
 	# GDT, paging, and other features
 	call gdt_install
+	# load the TSS which is in the 6th entry of the GDT
+	movw $0x28, %ax
+	ltr %ax
 
 boot_kernel:
 	# enter high-level kernel (C)

src/kernel/arch/x86/gdt.c

@@ -28,6 +28,7 @@
 #define GDT_SIZE 6
 
 struct segdesc gdt[GDT_SIZE];
+struct tss tss;
 struct segreg gdtr;
 
 void gdt_entry_set(struct segdesc *entry, uint32_t base,
@@ -57,9 +58,13 @@ void gdt_install() {
 	// user
 	gdt_entry_set(&gdt[3], 0, 0xFFFFFFFF, 0xFA, 0xCF);
 	gdt_entry_set(&gdt[4], 0, 0xFFFFFFFF, 0xF2, 0xCF);
+
 	// TSS
-	// TODO: create a proper TSS
-	gdt_entry_set(&gdt[5], 0, 0, 0x91, 0x40);
+	tss.ss0 = 0x10;
+	// TODO: set esp0 for system interrupts
+	tss.iopb = sizeof(tss);
+	gdt_entry_set(&gdt[5], (uint32_t)&tss,
+			sizeof(tss), 0x89, 0x40);
 
 	gdt_flush(&gdtr);
 }

src/kernel/arch/x86/gdt.h

@@ -20,7 +20,7 @@
 
 #include "structs.h"
 
-extern void gdt_flush(struct segreg *gdtr);
+extern void gdt_flush(struct segreg*);
 void gdt_entry_set(struct segdesc *entry, uint32_t base,
 		uint32_t limit, uint8_t access, uint8_t gran);
 void gdt_install();

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;
+}

toolchains/i686-elf.cmake

@@ -2,7 +2,9 @@ set(CMAKE_SYSTEM_NAME Generic)
 set(CMAKE_SYSTEM_PROCESSOR i686)
 
 set(CMAKE_C_COMPILER i686-elf-gcc)
-set(CMAKE_C_COMPILER_WORKS TRUE)
-set(CMAKE_CXX_COMPILER i686-elf-g++)
-set(CMAKE_CXX_COMPILER_WORKS TRUE)
+set(CMAKE_C_FLAGS "-ffreestanding -fno-builtin" CACHE STRING "C flags for test compilation.")
+set(CMAKE_EXE_LINKER_FLAGS "-ffreestanding -nostdlib" CACHE STRING "Linker flags for test compilation.")
+set(CMAKE_TRY_COMPILE_PLATFORM_VARIABLES CMAKE_C_FLAGS)
 set(CMAKE_ASM_COMPILER i686-elf-as)
+
+set(64BIT FALSE CACHE BOOL "Whether the architecture supports 64-bit.")