x86_64: add temporary serial driver for printk

arch/x86_64/include/arch/serial.h

@@ -0,0 +1,17 @@
+#ifndef ARCH_SERIAL_H_
+#define ARCH_SERIAL_H_
+
+#define SERIAL_PORT_A 0x3F8
+#define SERIAL_PORT_B 0x2F8
+#define SERIAL_PORT_C 0x3E8
+#define SERIAL_PORT_D 0x2E8
+
+extern void serial_putchar(int port, char ch);
+
+extern void serial_wait(int device);
+extern void serial_send_byte(int device, char out);
+extern char serial_recv_byte(int device);
+
+extern int serial_rcvd(int device);
+
+#endif

arch/x86_64/serial.c

@@ -0,0 +1,30 @@
+#include <arch/serial.h>
+#include <arch/ports.h>
+
+static int transmit_empty(int device)
+{
+    return inportb(device + 5) & 0x20;
+}
+
+void serial_send_byte(int device, char out)
+{
+    unsigned int _count = 0;
+    while (!transmit_empty(device)) {
+        _count++;
+    }
+
+    outportb(device, out);
+
+    while (!transmit_empty(device)) {
+        _count++;
+    }
+}
+
+void serial_putchar(int port, char ch)
+{
+    if (ch == '\n') {
+        serial_send_byte(port, '\r');
+    }
+
+    serial_send_byte(port, ch);
+}

arch/x86_64/vgacon.c

@@ -1,3 +1,4 @@
+#include <arch/serial.h>
 #include <socks/libc/string.h>
 #include <socks/libc/ctype.h>
 #include <arch/ports.h>
@@ -75,6 +76,8 @@ static void handle_ctrl(int c)
 
 static void vgacon_putchar(int c)
 {
+	serial_putchar(SERIAL_PORT_A, c);
+
 	if (iscntrl(c)) {
 		handle_ctrl(c);
 		return;