Implemented simple Multiboot1 kernel

kernel/kernel.c

@@ -0,0 +1,200 @@
+#include "stdint.h"
+#include "multiboot.h"
+
+/* Constants */
+#define COLS	80
+#define ROWS	24
+#define ATTR	0x0f
+#define VID_MEM	0xb8000
+
+/* Variables */
+static int xpos;
+static int ypos;
+static uint8_t* video;
+
+/* Forward Declarations */
+void cls(void);
+void itoa(char* buf, int base, int d);
+void putc(int c);
+void printf(const char* fmt, ...);
+
+/* Entry Point */
+void kmain(void) {
+	uint32_t magic, addr;
+	__asm__ volatile ("movl %%eax, %0; movl %%ebx, %1" : "=m"(magic), "=m"(addr));
+	struct multiboot_info* mbi;
+  	video = (uint8_t*)VID_MEM;
+
+	// Clear Screen
+	cls();
+
+	// Didn't boot with Multiboot
+	if (magic != BOOT_MAGIC) {
+		printf("Invalid Magic Number: 0x%x\n", magic);
+		while (1);
+	}
+	
+	mbi = (struct multiboot_info*)addr;
+
+	printf("flags: 0x%x\n", mbi->flags);
+
+	if (mbi->flags & MBI_MEMORY) {
+		printf("mem_lower: %ukB, mem_upper: %ukB\n", 
+			mbi->mem_lower, mbi->mem_upper);
+	}
+
+	if (mbi->flags & MBI_BOOT_DEV) {
+		printf("boot_device: 0x%x\n", mbi->boot_device);
+	}
+
+	if (mbi->flags & MBI_CMDLINE) {
+		printf("cmdline: %s\n", mbi->cmdline);
+	}
+
+	if (mbi->flags & MBI_MODS) {
+		printf("mods_count: %d, mods_addr: 0x%x\n",
+			mbi->mods_count, mbi->mods_addr);
+
+		struct multiboot_module* mod = 
+			(struct multiboot_module*)mbi->mods_addr;
+
+		for (size_t i = 0; i < mbi->mods_count; i++) {
+			printf("  start 0x%x, end: 0x%x, cmdline: %s\n",
+				mod->start, mod->end, mod->cmdline);
+			mod++;
+		}
+	}
+
+	if (mbi->flags & MBI_SYMBOLS &&
+	    mbi->flags & MBI_ELF_HEAD) {
+		printf("Flag SYMBOLS and ELF HEADER are both set!\n");
+		while (1);
+	}
+
+	if (mbi->flags & MBI_MEMMAP) {
+		printf("mmap_addr: 0x%x, mmap_length: 0x%x\n",
+			mbi->mmap_addr, mbi->mmap_length);
+
+		struct multiboot_memmap* mmap = 
+			(struct multiboot_memmap*)mbi->mmap_addr;
+
+		while ((uint32_t)mmap < mbi->mmap_addr + mbi->mmap_length) {
+			printf(	"  size: 0x%x, base: 0x%08x, "
+				"length: 0x%08x, type: 0x%x\n",
+				mmap->size, mmap->base, mmap->len, mmap->type);
+
+			mmap = (struct multiboot_memmap*)
+				((uint32_t)mmap + mmap->size + (sizeof(mmap->size)));
+		}
+	}
+
+	while (1);
+}
+
+void cls(void) {
+	for (int i = 0; i < COLS * ROWS * 2; i++) video[i] = 0;
+	xpos = 0;
+	ypos = 0;
+}
+
+void itoa(char* buf, int base, int d) {
+	char* p = buf;
+	char* p1;
+	char* p2;
+	uint32_t ud = d;
+	int divisor = 10;
+
+	if (base == 'd' && d < 0) {
+		*p++ = '-';
+		buf++;
+		ud = -d;
+	} else if (base == 'x') divisor = 16;
+
+	do {
+		int remainder = ud % divisor;
+		*p++ = (remainder < 10) ? remainder + '0' : remainder + 'a' - 10;
+	} while (ud /= divisor);
+
+	*p = 0;
+
+	p1 = buf;
+	p2 = p - 1;
+	while (p1 < p2) {
+		char tmp = *p1;
+		*p1 = *p2;
+		*p2 = tmp;
+		p1++;
+		p2--;
+	}
+}
+
+/* Put the character C on the screen. */
+void putc(int c) {
+	if (c == '\n' || c == '\r') {
+	newline:
+		xpos = 0;
+		ypos++;
+		if (ypos >= ROWS)
+		ypos = 0;
+		return;
+	}
+
+	video[(xpos + ypos * COLS) * 2] = c & 0xFF;
+	video[(xpos + ypos * COLS) * 2 + 1] = ATTR;
+
+	xpos++;
+	if (xpos >= COLS)
+	goto newline;
+}
+
+void printf(const char *format, ...) {
+	char** arg = (char**)&format;
+	int c;
+	char buf[20];
+
+	arg++;
+
+	while ((c = *format++) != 0) {
+		if (c != '%') { 
+			putc (c);
+			continue;
+		}
+		
+		char *p, *p2;
+		int pad0 = 0, pad = 0;
+		
+		c = *format++;
+		
+		if (c == '0') {
+			pad0 = 1;
+			c = *format++;
+		}
+
+		if (c >= '0' && c <= '9') {
+			pad = c - '0';
+			c = *format++;
+		}
+
+		switch (c) {
+		case 'd':
+		case 'u':
+		case 'x':
+			itoa(buf, c, *((int *) arg++));
+			p = buf;
+			goto string;
+			break;
+		case 's':
+			p = *arg++;
+			if (! p) p = "(null)";
+		string:
+			for (p2 = p; *p2; p2++);
+			for (; p2 < p + pad; p2++) putc (pad0 ? '0' : ' ');
+			while (*p) putc (*p++);
+			break;
+		default:
+			putc(*((int *) arg++));
+			break;
+		}
+	}
+}
+