feat(stdio): add the printf function to the kernel

Makefile

@@ -1,6 +1,6 @@
 all: kernel loader
 
-OBJS := main.o gdt.o page.o
+OBJS := main.o gdt.o page.o stdio.o
 
 kernel: kernel.lds kernel.o $(OBJS)
 	ld -Tkernel.lds kernel.o -o kernel $(OBJS)

main.c

@@ -5,6 +5,8 @@
 #include "msr.h"
 #include "page.h"
 #include "io.h"
+#include "stdio.h"
+
 char hello[] = "Hello, C world!";
 
 void *memset(void *s, int c, size_t n) {
@@ -81,15 +83,7 @@ void sys_print(unsigned x, unsigned y, uint16_t *chars, unsigned n) {
 }
 
 void sys_setcursor(unsigned x, unsigned y) {
-	if (x >= 80)
-		return;
-	if (y >= 25)
-		return;
-	unsigned addr = x + y * 80;
-	outb(0x3d4, 0xe);
-	outb(0x3d5, addr >> 8);
-	outb(0x3d4, 0xf);
-	outb(0x3d5, addr);
+	setcursor(x, y);
 }
 
 int kbd_getbyte(void) {
@@ -167,6 +161,11 @@ __asm__(
 extern void user_prog;
 
 void main() {
+	clrscr();
+	for (int i = 97; i < 127; i++) {
+		printf("printf demo: char=%c, dec=%d, hex=%x, str comment = %s\n", i, i, i, "\"no comment\"");
+	}
+
 	init_gdt();
 	init_pg();
 	// ELF loader start

stdio.c

@@ -0,0 +1,156 @@
+#include <stdarg.h>
+#include <stdint.h>
+#include "stdio.h"
+#include "io.h"
+
+
+#define VGA_WRITE_START 0xffff8000000b8000ull
+#define DEFAULT_FORCOLOR 0x0d
+#define DEFAULT_BACKCOLOR 0x0f
+#define WIDTH 80
+#define HEIGHT 25
+
+
+uint16_t screen[WIDTH * HEIGHT];
+int cur_x = 0;
+int cur_y = 0;
+
+
+static void writec(char c, unsigned x, unsigned y, uint8_t forecolor, uint8_t backcolor) {
+    uint16_t colors = (backcolor << 4) | (forecolor & 0x0F);
+    uint16_t write_arg = c | colors << 8;
+    unsigned pos = y * WIDTH + x;
+    screen[pos] = write_arg;
+    ((uint16_t*)VGA_WRITE_START)[pos] = screen[pos];
+}
+
+void setcursor(unsigned x, unsigned y) {
+    if (x >= WIDTH)
+        return;
+    if (y >= HEIGHT)
+        return;
+    unsigned addr = x + y * 80;
+    outb(0x3d4, 0xe);
+    outb(0x3d5, addr >> 8);
+    outb(0x3d4, 0xf);
+    outb(0x3d5, addr);
+}
+
+static void scroll(void) {
+    for (unsigned y = 1; y < HEIGHT; y++) {
+        for (unsigned x = 0; x < WIDTH; x++) {
+            unsigned src_pos = y * WIDTH + x;
+            unsigned dst_pos = (y - 1) * WIDTH + x;
+            screen[dst_pos] = screen[src_pos];
+            ((uint16_t*)VGA_WRITE_START)[dst_pos] = screen[dst_pos];
+        }
+    }
+
+    for (unsigned x = 0; x < WIDTH; x++) {
+        writec(' ', x, HEIGHT - 1, DEFAULT_FORCOLOR, DEFAULT_BACKCOLOR);
+    }
+}
+
+void clrscr(void) {
+    for (unsigned x = 0; x < WIDTH; x++) {
+        for (unsigned y = 0; y < HEIGHT; y++) {
+            writec(' ', x, y, DEFAULT_FORCOLOR, DEFAULT_BACKCOLOR);
+        }
+    }
+    setcursor(0, 0);
+}
+
+void putc(uint8_t c) {
+    if (c == '\n') {
+        cur_x = 0;
+        cur_y++;
+    }
+    else {
+        writec(c, cur_x, cur_y, DEFAULT_FORCOLOR, DEFAULT_BACKCOLOR);
+        cur_y = (cur_x + 1 == WIDTH) ? cur_y + 1 : cur_y;
+        cur_x = (cur_x + 1) % WIDTH;
+    }
+
+    if (cur_y == HEIGHT) {
+        scroll();
+        cur_y--;
+    }
+    setcursor(cur_x, cur_y);
+}
+
+static void print_char(char c) {
+    putc(c);
+}
+
+static void print_str(uint8_t* str) {
+    while (*str) {
+        putc(*str);
+        str++;
+    }
+}
+
+static void print_num(uint32_t num, uint8_t base) {
+    uint32_t tmp;
+    uint8_t i = 0;
+    uint8_t digits[8] = { 0 };
+
+    if (!num) {
+        putc('0');
+        return;
+    }
+
+    while (num) {
+        tmp = num;
+        num /= base;
+        digits[i] = "0123456789abcdef"[tmp - (num * base)];
+        i++;
+    }
+
+    for (int j = i - 1; j >= 0; j--) {
+        putc(digits[j]);
+    }
+}
+
+void printf(uint8_t* format, ...) {
+    va_list va;
+    va_start(va, format);
+    uint8_t c, b;
+    uint8_t* str;
+    uint32_t num;
+
+    while (*format) {
+        c = *format;
+        if (c != '%') {
+            putc(c);
+        }
+        else {
+            format++;
+            c = *format;
+
+            switch(c) {
+                case 'c':
+                    b = (uint8_t) va_arg(va, uint32_t);
+                    print_char(b);
+                    break;
+                case 's':
+                    str = va_arg(va, uint8_t*);
+                    print_str(str);
+                    break;
+                case 'd':
+                    num = va_arg(va, uint32_t);
+                    print_num(num, 10);
+                    break;
+                case 'x':
+                    num = va_arg(va, uint32_t);
+                    putc('0');
+                    putc('x');
+                    print_num(num, 16);
+                    break;
+            }
+        }
+
+        format++;
+    }
+
+    va_end(va);
+}

stdio.h

@@ -0,0 +1,9 @@
+#ifndef STDIO_H
+#define STDIO_H
+
+void clrscr(void);
+void setcursor(unsigned x, unsigned y);
+void putc(uint8_t c);
+void printf(uint8_t* format, ...);
+
+#endif