Paging, interrupts

kernel/Makefile

@@ -13,7 +13,7 @@ EXEC_PREFIX?=$(PREFIX)
 BOOTDIR?=$(EXEC_PREFIX)/boot
 INCLUDEDIR?=$(PREFIX)/include
 
-CFLAGS:=$(CFLAGS) -ffreestanding -Wall -Wextra -fstack-protector
+CFLAGS:=$(CFLAGS) -ffreestanding -Wall -Wextra -fstack-protector-strong -mgeneral-regs-only -mno-red-zone
 CPPFLAGS:=$(CPPFLAGS) -D__is_kernel -Iinclude
 LDFLAGS:=$(LDFLAGS)
 LIBS:=$(LIBS) -nostdlib -lk -lgcc

kernel/arch/i386/boot/boot.S

@@ -26,7 +26,8 @@ stack_top:
 _start:
     movl $stack_top, %esp
     cli
-    call gdt_init          # call global constructors
+    call gdt_init           # initialize the GDT
+    call idt_init           # initialize the IDT
     call kernel_main        # transfer control to main kernel
     # Hang if kernel_main unexpectedly returns
 1:  hlt

kernel/arch/i386/boot/gdt.c

@@ -41,7 +41,7 @@ void gdt_init(void) {
         gdt_fill(GDT+i, rows+i);
     }
 
-    gp.base = (void*) GDT;
+    gp.base = &GDT;
     gp.limit = (GDT_ENTRIES * sizeof(gdt_entry)) - 1;
 
     gdt_load();

kernel/arch/i386/boot/idt.c

@@ -0,0 +1,49 @@
+#include <kernel/idt.h>
+#include <stdio.h>
+
+__attribute__((interrupt)) void hello_interrupt(idt_frame* frame) {
+    printf("Hello from interrupt!\n");
+    printf("ip=0x%x, cs=0x%x, flags=0b%b\n", frame->ip, frame->cs, frame->flags);
+}
+
+__attribute__((interrupt)) void hello_interrupt_err(idt_frame_err* frame) {
+    printf("Hello from error interrupt!\n");
+    printf("ip=0x%x, cs=0x%x, flags=0b%b, err=0x%x\n", frame->ip, frame->cs, frame->flags, frame->err);
+    asm volatile("cli; hlt");
+}
+
+void idt_fill_row(idt_entry_t* target, idt* source) {
+    target->isr_low = source->offset & 0xFFFF;
+    target->isr_high = (source->offset >> 16) & 0xFFFF;
+    target->kernel_cs = source->segment;
+    target->flags = 0x80;
+    target->flags |= (source->ring & 0x3) << 5;
+    target->flags |= (source->gate & 0xF);
+    target->reserved = 0;
+}
+
+__attribute__((aligned(0x10))) idt_entry_t IDT[IDT_ROWS];
+idtr_t idtptr;
+
+void idt_init(void) {
+    idt rows[] = {
+        {(uint32_t)hello_interrupt, 0x08, INT_GATE32, 0},
+        {(uint32_t)hello_interrupt_err, 0x08, INT_GATE32, 0},
+    };
+
+    int valid_rows = sizeof(rows) / sizeof(idt_entry_t);
+
+    for(int i = 0; i < valid_rows; ++i) {
+        idt_fill_row(IDT+i, rows+i);
+    }
+
+    idt blank_row = {0, 0, 0, 0};
+    for(int i = valid_rows; i < IDT_ROWS; ++i) {
+        idt_fill_row(IDT+i, &blank_row);
+    }
+
+    idtptr.base = &IDT;
+    idtptr.limit = (IDT_ROWS * sizeof(idt_entry_t)) - 1;
+
+    idt_load();
+}

kernel/arch/i386/boot/idt_load.S

@@ -0,0 +1,6 @@
+.global idt_load
+.type idt_load, @function
+idt_load:
+    lidt (idtptr)
+    sti
+    ret

kernel/arch/i386/make.config

@@ -7,4 +7,7 @@ KERNEL_ARCH_OBJS=\
 $(ARCHDIR)/boot/boot.o \
 $(ARCHDIR)/vga/tty.o \
 $(ARCHDIR)/boot/gdt.o \
-$(ARCHDIR)/boot/gdt_load.o
+$(ARCHDIR)/boot/gdt_load.o \
+$(ARCHDIR)/paging/paging.o \
+$(ARCHDIR)/boot/idt.o \
+$(ARCHDIR)/boot/idt_load.o

kernel/arch/i386/paging/paging.S

@@ -0,0 +1,22 @@
+.text
+.globl load_page_dir
+load_page_dir:
+    push %ebp
+    mov %esp, %ebp
+    mov 8(%esp), %eax
+    mov %eax, %cr3
+    mov %ebp, %esp
+    pop %ebp
+    ret
+
+.text
+.globl enable_paging
+enable_paging:
+    push %ebp
+    mov %esp, %ebp
+    mov %cr0, %eax
+    or $0x80000000, %eax
+    mov %eax, %cr0
+    mov %ebp, %esp
+    pop %ebp
+    ret

kernel/arch/i386/vga/tty.c

@@ -41,8 +41,13 @@ void terminal_putentryat(unsigned char c, uint8_t color, size_t x, size_t y) {
 void terminal_putchar(char c) {
     unsigned char uc = c;
 
+    if (uc == '\n') {
+        terminal_column = 0;
+        if (++terminal_row == VGA_HEIGHT) {
+            terminal_row = 0;
+        }
+    } else {
         terminal_putentryat(uc, terminal_color, terminal_column, terminal_row);
-
         if (++terminal_column == VGA_WIDTH) {
             terminal_column = 0;
             if (++terminal_row == VGA_HEIGHT) {
@@ -50,6 +55,7 @@ void terminal_putchar(char c) {
             }
         }
     }
+}
 
 void terminal_write(const char* data, size_t size) {
     for (size_t i = 0; i < size; i++) {

kernel/include/kernel/gdt.h

@@ -1,5 +1,5 @@
 /**
- * Referenced from https://tendstofortytwo/clay
+ * Referenced from https://github.com/tendstofortytwo/clay
  * kernel/kernel.c
  */
 

kernel/include/kernel/idt.h

@@ -0,0 +1,53 @@
+#ifndef _KERNEL_IDT_H
+#define _KERNEL_IDT_H
+
+#include <stdint.h>
+
+#define IDT_ROWS 256
+#define TASK_GATE 0x5
+#define INT_GATE16 0x6
+#define TRAP_GATE16 0x7
+#define INT_GATE32 0xE
+#define TRAP_GATE32 0xF
+
+typedef struct {
+    uint16_t limit;
+    uint32_t base;
+} __attribute__((packed)) idtr_t;
+
+typedef struct {
+    uint16_t isr_low; // lower 16-bits of ISR address
+    uint16_t kernel_cs; // The GDT selector that the CPU will load into CS before calling ISR
+    uint8_t reserved; // set to zero
+    uint8_t flags; // Type and attributes
+    uint16_t isr_high; // Higher 16-bits of ISR address
+} __attribute__((packed)) idt_entry_t;
+
+typedef struct {
+    uint32_t offset;
+    uint16_t segment;
+    uint8_t gate;
+    uint8_t ring;
+} idt;
+
+typedef struct {
+    uint32_t ip;
+    uint32_t cs;
+    uint32_t flags;
+    uint32_t sp;
+    uint32_t ss;
+} __attribute__((packed)) idt_frame;
+
+typedef struct {
+    uint32_t err;
+    uint32_t ip;
+    uint32_t cs;
+    uint32_t flags;
+    uint32_t sp;
+    uint32_t ss;
+} __attribute__((packed)) idt_frame_err;
+
+extern void idt_load();
+extern idtr_t idtptr;
+
+#endif

kernel/include/kernel/paging.h

@@ -0,0 +1,7 @@
+#ifndef _KERNEL_PAGING_H
+#define _KERNEL_PAGING_H
+
+extern void load_page_dir(unsigned int*);
+extern void enable_paging();
+
+#endif

kernel/kernel/exception.c

@@ -0,0 +1,8 @@
+#include <stdio.h>
+
+__attribute__((noreturn))
+void exception_handler(void);
+void exception_handler() {
+    printf("Kernel exception!\n");
+    __asm__ volatile ("cli; hlt");
+}

kernel/kernel/kernel.c

@@ -2,8 +2,35 @@
 
 #include <kernel/tty.h>
 #include <kernel/gdt.h>
+#include <kernel/paging.h>
+
+#define PAGE_ENTRIES 1024
+#define PAGE_SIZE 4 * PAGE_ENTRIES
+
+void paging_init() {
+    uint32_t page_dir[PAGE_ENTRIES] __attribute__((aligned(PAGE_SIZE)));
+    for(int i = 0; i < PAGE_ENTRIES; i++) {
+        // Supervisor: only kernel-mode can access
+        // Write Enabled: Can be both read and written to
+        // Not Present: Page table not present
+        page_dir[i] = 0x00000002;
+    }
+
+    uint32_t first_page_table[PAGE_ENTRIES] __attribute__((aligned(PAGE_SIZE)));
+    for(unsigned int i = 0; i < PAGE_ENTRIES; i++) {
+        // As the address is page aligned, it will leave 12 bits zeroed,
+        // which are used by the attributes.
+        first_page_table[i] = (i * 0x1000) | 3; // attr: supervisor, r/w, present
+    }
+
+    page_dir[0] = ((unsigned int)first_page_table) | 3; //attr: supervisor, r/w, present
+
+    load_page_dir(page_dir);
+    enable_paging();
+}
 
 void kernel_main(void) {
+    paging_init();
     terminal_initialize();
     printf("Hello, kernel World!\n");
     printf("String test: %s\n", "HELLOOOOO");
@@ -11,4 +38,6 @@ void kernel_main(void) {
     printf("Int test: %d\n", 747474);
     printf("Hex test: 0x%x\n", 0xDEADBEEF);
     printf("And now for 0.1 + 0.2...... which is: %.17f\n", 0.1 + 0.2);
+    asm("int $0");
+    asm("cli");
 }