Kernel/Userspace: Start initial work on userspace and syscalls

kernel/userspace/userspace.cpp

@@ -0,0 +1,28 @@
+#include <BAN/Formatter.h>
+#include <kernel/Syscall.h>
+
+#define USERSPACE __attribute__((section(".userspace")))
+
+USERSPACE int syscall(int syscall, void* arg1 = nullptr, void* arg2 = nullptr, void* arg3 = nullptr)
+{
+	int ret;
+	asm volatile("int $0x80" : "=a"(ret) : "a"(syscall), "b"(arg1), "c"(arg2), "d"(arg3) : "memory");
+	return ret;
+}
+
+USERSPACE void user_putc(char ch)
+{
+	syscall(SYS_PUTC, (void*)(uintptr_t)ch);
+}
+
+USERSPACE void print(const char* str)
+{
+	while (*str)
+		user_putc(*str++);
+}
+
+USERSPACE void userspace_entry()
+{
+	BAN::Formatter::println(user_putc, "Hello {}!", "World");
+	for (;;);
+}