Paging!!

.ccls

@@ -0,0 +1,2 @@
+clang
+-Isrc/include

Makefile

@@ -9,15 +9,17 @@ CFLAGS?=
 ASFLAGS?=
 
 # Define flags for C files
+
 CFLAGS:=\
 -O2 \
--std=gnu99 \
 -ffreestanding \
 -Wall -Wextra \
--Wno-incompatible-pointer-types\
+-fno-exceptions -fno-rtti \
 -I$(INCLUDEDIR) \
 $(CFLAGS)
 
+CXXFLAGS:=$(CFLAGS)
+
 # Define flags for assembly files
 ASFLAGS:=\
 -I$(SOURCEIDR)$(INCLUDEDIR) \
@@ -31,7 +33,10 @@ LINKERFLAGS:=\
 -lgcc
 
 LIB_OBJS=\
-$(BUILDDIR)$(ARCHDIR)bootstrap.o
+$(BUILDDIR)$(ARCHDIR)bootstrap.o \
+$(BUILDDIR)$(ARCHDIR)paging.o \
+$(BUILDDIR)$(ARCHDIR)initialize_pages.o \
+$(BUILDDIR)$(ARCHDIR)tty.o
 
 KERNEL_OBJS=\
 $(BUILDDIR)kernel/kernel.o
@@ -43,6 +48,9 @@ LINKER_PATH=$(SOURCEDIR)$(ARCHDIR)linker.ld
 .PHONY: all clean snowstorm.iso debug
 .SUFFIXES: .c .o .s
 
+$(BUILDDIR)%.o : $(SOURCEDIR)%.cpp
+	i686-elf-g++ -c $< -o $@ $(CXXFLAGS)
+
 $(BUILDDIR)%.o : $(SOURCEDIR)%.c
 	i686-elf-gcc -c $< -o $@ $(CFLAGS)
 
@@ -61,11 +69,11 @@ snowstorm.kernel: $(OBJS)
 	i686-elf-gcc -T $(LINKER_PATH) -o build/snowstorm.kernel $(OBJS) $(LINKERFLAGS) 
 	grub-file --is-x86-multiboot build/snowstorm.kernel
 
-debug: CFLAGS += -g -O0
+debug: CXXFLAGS += -g -O1
 debug: ASFLAGS += -g
+debug: CFLAGS += -g -O1
 debug: all
 
-
 clean:
 	rm -f $(OBJS)
 	rm -f build/snowstorm.kernel
@@ -76,7 +84,5 @@ run: all
 	qemu-system-i386 -d int -no-reboot -kernel build/snowstorm.kernel
 
 run-debug: debug
-	qemu-system-i386 -d int -no-reboot -S -gdb tcp::9000 build/snowstorm.iso
-
-run-debug-kernel: debug
 	qemu-system-i386 -d int -no-reboot -S -gdb tcp::9000 -kernel build/snowstorm.kernel
+

src/arch/i686/bootstrap.s

@@ -12,26 +12,20 @@
 .long FLAGS
 .long CHECKSUM
 
-.section .bss, "aw", @nobits
+.section .multiboot.bss, "aw", @nobits
 .align 16
 stack_bottom:
 .skip (1 << 16) # 64 KiB
 stack_top:
 
-.global boot_page_directory
- 	.align 4096
-boot_page_directory:
-	.skip 4096
-boot_page_table1:
-    .skip 4096
-
 .section .multiboot.text, "a"
 .global _start
 .type _start, @function
-.extern kernel_main
 _start:
 	mov $stack_top, %esp # The stack grows downwards so it starts at the top
-    # (We kind of need to have a stack to do anything)
+    # (We kind of need to have a stack to do anything in a high-level language)
+
+    call initialize_pages
 
     call kernel_main
 

src/arch/i686/initialize_pages.c

@@ -0,0 +1,74 @@
+#include <stdint.h>
+#include <stdbool.h>
+#include "units.h"
+
+struct PageDirectoryEntry {
+    bool present : 1;
+    bool write : 1;
+    bool user : 1;
+    bool write_through : 1;
+    bool cache_disabled : 1;
+    bool accessed : 1;
+    bool available_2 : 1;
+    bool size : 1;
+    size_t available_1 : 4;
+    size_t page_table_address : 20;
+} __attribute__((packed)); // Force the compiler to keep our structure intact.
+
+struct PageTableEntry {
+    bool present : 1;
+    bool write : 1;
+    bool user : 1;
+    bool write_through : 1;
+    bool cache_disabled : 1;
+    bool accessed : 1;
+    bool dirty : 1;
+    bool pat : 1;
+    bool global : 1;
+    size_t available : 3;
+    size_t physical_address : 20;
+} __attribute__((packed));
+
+extern const size_t _kernel_start;
+extern const size_t _kernel_end;
+
+struct PageDirectoryEntry _page_directory[1024] __attribute__((aligned(4096))); // Create a page directory with 1024 entries and make sure it's 4 KiB aligned
+
+// Identity page table for lowest 4 MiB, including this
+struct PageTableEntry _identity_page_table[1024] __attribute__((aligned(4096)));
+
+// Assumes kernel is smaller than 4 MiB, should change later
+struct PageTableEntry _kernel_page_table[1024] __attribute__((aligned(4096)));
+
+void initialize_pages() {
+    struct PageDirectoryEntry identity_pd_entry = {
+        .page_table_address = (size_t)(_identity_page_table) >> 12,
+        .size = false, // Small (4 KiB) Pages
+        .user = false, // Ring 3 can't access
+        .write = true, // Write enabled
+        .present = true, 
+    };
+
+    _page_directory[0] = identity_pd_entry;
+
+    // Identity page lowest 4 MiB to not crash instantly
+    for (size_t i = 0; i < mib(4) / kib(4); i++) {
+        struct PageTableEntry table_entry = {
+            .physical_address = i,
+            .user = false,
+            .write = true,
+            .present = true,
+        };
+        _identity_page_table[i] = table_entry;
+    }
+
+    _page_directory[768] = identity_pd_entry;
+
+    asm("mov %0, %%cr3" :: "r" (_page_directory));
+    uint32_t control_register_0;
+    asm("mov %%cr0, %0" : "=r" (control_register_0));
+    // Enable the paging bit
+    control_register_0 = control_register_0 | 0x80000000;
+    asm("mov %0, %%cr0" :: "r" (control_register_0));
+}
+

src/arch/i686/linker.ld

@@ -3,27 +3,55 @@ ENTRY(_start)
 
 SECTIONS
 {
-    /* Leave 1 Megabyte for GRUB */
-	. = 1M;
+    /* Leave 2 Mibibytes for GRUB */
+	. = 2M;
     
     .multiboot.data : 
     {
         *(.multiboot.data) /* Take the data from label .multiboot.data from all files and put it in our output file */
     }
 
-    .multiboot.text : 
+    .multiboot.text BLOCK(4K) : ALIGN(4K)
     {
-        *(.multiboot.text) /* Take the data from label .multiboot.data from all files and put it in our output file */
+        *(.multiboot.text) 
     }
     
-    .bss : 
+    .multiboot.bss : 
     {
-        *(.bss) /* Take the data from label .multiboot.data from all files and put it in our output file */
+        *(.multiboot.bss) /* Take the data from label .multiboot.data from all files and put it in our output file */
     }
 
-    .data : 
-    {
-        *(.data) /* Take the data from label .multiboot.data from all files and put it in our output file */
+    .pages.bss : ALIGN(4K) {
+        *initialize_pages.o(.bss)
     }
 
+    .pages.data : ALIGN(4K) {
+        *initialize_pages.o(.data)
+    }
+
+    .pages.text : ALIGN(4K) {
+        *initialize_pages.o(.text)
+    }
+
+    _kernel_start = .;
+
+    /* Higher half kernel */
+    . += 0xC0000000;
+
+    .data BLOCK(4K) : AT (ADDR (.data) - 0xC0000000)
+    {
+        EXCLUDE_FILE (*initialize_pages.o) *(.data) 
+    }
+
+    .bss BLOCK(4K) :  AT (ADDR (.bss)  - 0xC0000000)
+    {
+        EXCLUDE_FILE (*initialize_pages.o) *(.bss) 
+    }
+
+    .text BLOCK(4K) : AT (ADDR (.text) - 0xC0000000)
+    {
+        EXCLUDE_FILE (*initialize_pages.o) *(.text) 
+    }
+    
+    _kernel_end = .;
 }

src/arch/i686/paging.cpp

@@ -0,0 +1,123 @@
+#include <stdint.h>
+#include "arch/paging.hpp"
+#include "units.h"
+
+/*
+* When doing paging on x86, we need to keep track of a few things.
+* The "Page Directory" is a 4 KiB aligned table containing 1024 entries, each of which point to a "Page Table", which also is a 4 KiB table with 1024 entries where each entry points to a 4 KiB page.
+* When accessing virtual memory, the MMU will take the first 10 bits to index into the page directory and lookup the corresponding page table. 
+* It will then use the next 10 bits to index into the page table. Then it will use the last 12 bits as an offset into the page, returning that byte.
+* (And a lot of complicated other caching stuff that we don't need to worry to much about)
+*
+* Paging is very important since every program wants the same region of memory, and paging makes them think they get the memory that they want.
+*
+*/
+
+/*
+*
+* I want to both have a nice user interface, but also a bit of low-level control for the rest of the kernel
+*
+*
+*
+*/
+
+#define NUM_PAGES 32768
+
+// Make a list of 32768 pages, representing 128 MiB of physical memory
+Page pages[NUM_PAGES];
+
+struct PageDirectoryEntry {
+    uint32_t page_table_address : 20;
+    uint32_t available_1 : 4;
+    bool size : 1;
+    bool available_2 : 1;
+    bool accessed : 1;
+    bool cache_disabled : 1;
+    bool write_through : 1;
+    bool user : 1;
+    bool write : 1;
+    bool present : 1;
+} __attribute__((packed)); // Force the compiler to keep our structure intact.
+
+struct PageTableEntry {
+    uint32_t physical_address : 20;
+    uint32_t available : 3;
+    bool global : 1;
+    bool pat : 1;
+    bool dirty : 1;
+    bool accessed : 1;
+    bool cache_disabled : 1;
+    bool write_through : 1;
+    bool user : 1;
+    bool write : 1;
+    bool present : 1;
+} __attribute__((packed));
+
+PageDirectoryEntry dynamic_page_table[1024] __attribute__((aligned(4096))); // Create a page directory with 1024 entries and make sure it's 4 KiB aligned
+
+Page::Page() { }
+
+Page* Page::alloc(void* virtual_addr) {
+    int i = 0;
+    while (pages[i].present && i < NUM_PAGES) { i++; }
+
+    pages[i].virtual_addr = virtual_addr;
+    pages[i].present = true;
+
+    return pages + i;
+}
+
+Page* Page::alloc_fixed(void* physical_address, void* virtual_addr) {
+    Page* page = Page::from_physical(physical_address);
+    if (page->exists()) { return 0; }
+
+    page->present = true;
+    page->virtual_addr = virtual_addr;
+
+    return page;
+}
+
+void Page::free() {
+    this->unload();
+    this->present = false;
+}
+
+bool Page::load() {
+    return false;
+}
+
+bool Page::unload() {
+    return false;
+}
+
+bool Page::exists() {
+    return this->virtual_addr != 0;
+}
+
+void* Page::physical_location() {
+    return (void*)(0x1000 * (this - pages));
+}
+
+Page* Page::from_physical(void* physical_address) {
+    return pages + ((size_t)physical_address >> 12);
+}
+
+size_t Page::pd_entry() {
+    return (size_t)(this->virtual_addr) >> 22;
+}
+
+size_t Page::pt_entry() {
+    return ((size_t)(this->virtual_addr) >> 12) & ((1 << 10) - 1);
+}
+
+void Page::initialize() {
+    // Allocate the lowest 1 MiB of both virtual and physical memory to BIOS
+    for (size_t i = 0; i < mib(1); i += kib(4)) {
+        Page::alloc_fixed((void*)i, (void*)i);
+    }
+
+    /* for (size_t index = _kernel_start; index + kib(4) < _kernel_end; index += kib(4)) {
+        Page::alloc_fixed(void *physical_address, void *virtual_addr)
+    } */
+}
+

src/arch/i686/tty.c

@@ -0,0 +1,55 @@
+#include "arch/tty.h"
+#include <stddef.h>
+#include "strlib.h"
+
+#define VGA_WIDTH  80
+#define VGA_HEIGHT 25
+#define VGA_MEMORY 0xB8000
+
+int x = 0;
+int y = 0;
+uint16_t color = 0x0F;
+uint16_t* tty_buffer = (uint16_t*)VGA_MEMORY;
+
+void initialize_terminal() {
+    uint16_t entry = 0;
+    for (int y = 0; y < VGA_HEIGHT; y++) {
+        for (int x = 0; x < VGA_WIDTH; x++) {
+            write_character(x, y, entry);
+        }
+    }
+}
+
+uint16_t character_data(char character, uint8_t color) {
+    return character | (color << 8);
+}
+
+void write_character(int x, int y, uint16_t entry) {
+    size_t index = VGA_WIDTH * y + x;
+    tty_buffer[index] = entry;
+}
+
+void put_character(char character) {
+    if (character == '\n') {
+        y += 1;
+        x = 0;
+        return;
+    }
+
+    write_character(x, y, character_data(character, color));
+
+    x += 1;
+    if (x == VGA_WIDTH) {
+        x = 0;
+        y += 1;
+        if (y == VGA_HEIGHT) {
+            y = 0;
+        }
+    }
+}
+
+void write_string(char* str) {
+    for (size_t i = 0; i < strlen(str); i++) {
+        put_character(str[i]);
+    }
+}

src/include/arch/paging.hpp

@@ -0,0 +1,29 @@
+#include <stdbool.h>
+#include <stddef.h>
+
+class Page {
+private:
+    void* virtual_addr;
+    bool present;  
+    bool write_enable;
+    bool user;
+
+
+public:
+    Page();
+    static Page* alloc(void* virtual_addr);
+    static Page* alloc_fixed(void* physical_address, void* virtual_addr);
+    bool load();
+    bool unload();
+    bool exists();
+    void free();
+
+    void* physical_location();
+    static Page* from_physical(void* physical_address);
+
+    size_t pd_entry();
+    size_t pt_entry();
+
+    static void initialize();
+};
+

src/include/arch/tty.h

@@ -0,0 +1,27 @@
+#include <stdint.h>
+
+// TODO: Define colors
+enum vga_color {
+	VGA_COLOR_BLACK = 0,
+	VGA_COLOR_BLUE = 1,
+	VGA_COLOR_GREEN = 2,
+	VGA_COLOR_CYAN = 3,
+	VGA_COLOR_RED = 4,
+	VGA_COLOR_MAGENTA = 5,
+	VGA_COLOR_BROWN = 6,
+	VGA_COLOR_LIGHT_GREY = 7,
+	VGA_COLOR_DARK_GREY = 8,
+	VGA_COLOR_LIGHT_BLUE = 9,
+	VGA_COLOR_LIGHT_GREEN = 10,
+	VGA_COLOR_LIGHT_CYAN = 11,
+	VGA_COLOR_LIGHT_RED = 12,
+	VGA_COLOR_LIGHT_MAGENTA = 13,
+	VGA_COLOR_LIGHT_BROWN = 14,
+	VGA_COLOR_WHITE = 15,
+};
+
+void initialize_terminal();
+uint16_t character_data(char character, uint8_t color);
+void write_character(int x, int y, uint16_t entry);
+void put_character(char character);
+void write_string(char* str);

src/include/arch/tty.hpp

@@ -0,0 +1,27 @@
+#include <stdint.h>
+
+// TODO: Define colors
+enum vga_color {
+	VGA_COLOR_BLACK = 0,
+	VGA_COLOR_BLUE = 1,
+	VGA_COLOR_GREEN = 2,
+	VGA_COLOR_CYAN = 3,
+	VGA_COLOR_RED = 4,
+	VGA_COLOR_MAGENTA = 5,
+	VGA_COLOR_BROWN = 6,
+	VGA_COLOR_LIGHT_GREY = 7,
+	VGA_COLOR_DARK_GREY = 8,
+	VGA_COLOR_LIGHT_BLUE = 9,
+	VGA_COLOR_LIGHT_GREEN = 10,
+	VGA_COLOR_LIGHT_CYAN = 11,
+	VGA_COLOR_LIGHT_RED = 12,
+	VGA_COLOR_LIGHT_MAGENTA = 13,
+	VGA_COLOR_LIGHT_BROWN = 14,
+	VGA_COLOR_WHITE = 15,
+};
+
+extern "C" void initialize_terminal();
+extern "C" uint16_t character_data(char character, uint8_t color);
+extern "C" void write_character(int x, int y, uint16_t entry);
+extern "C" void put_character(char character);
+extern "C" void write_string(char* str);

src/include/units.h

@@ -0,0 +1,10 @@
+#include <stddef.h>
+
+static inline size_t kib(size_t amounts) {
+    return 1024 * amounts;
+}
+
+static inline size_t mib(size_t amounts) {
+    return 1024 * 1024 * amounts;
+}
+

src/kernel/kernel.c

@@ -1,12 +0,0 @@
-#include <stdbool.h>
-#include <stdint.h>
-#include "strlib.h"
-
-uint16_t* VGA_screen = (uint16_t*)0xB8000;
-char* text = "Hello World!";
-
-void kernel_main() {
-    for (int i = 0; i < strlen(text); i++) {
-        VGA_screen[i] = text[i] | 0x0F00; // 0x0F00: two bytes color, two bytes to combine it with text
-    }
-}

src/kernel/kernel.cpp

@@ -0,0 +1,18 @@
+#include <stdbool.h>
+#include <stdint.h>
+#include "strlib.h"
+#include "arch/paging.hpp"
+#include "arch/tty.hpp"
+
+uint16_t* VGA_screen = (uint16_t*)0xC00B8000;
+char* text = "Hello World!";
+
+extern "C" void kernel_main() {
+    initialize_terminal();
+
+    write_string(text);
+
+    Page::initialize();
+
+    while (true) { }
+}

src/kernel/pages.cpp

@@ -0,0 +1 @@
+