Implement syscalls, hello world from userspace

kernel/syscall/syscall.c

@@ -0,0 +1,27 @@
+#include <stdint.h>
+#include "syscall.h"
+#include "errors.h"
+#include "dlmalloc/malloc.h"
+#include "kprintf.h"
+#include "proc/proc.h"
+
+int32_t SYSCALL2(sys_debugprint, string1, len) {
+  char *buf = dlmalloc(len);
+  if (buf == NULL) {
+    return E_NOMEMORY;
+  }
+  ksnprintf(buf, len, "%s", string1);
+  kprintf("%s\n", buf);
+  dlfree(buf);
+  return E_OK;
+}
+
+int32_t SYSCALL0(sys_quitproc) {
+  proc_killself();
+  return E_OK;
+}
+
+SyscallFn SYSCALL_TABLE[SYSCALLS_MAX] = {
+  [SYS_DEBUGPRINT] = &sys_debugprint,
+  [SYS_QUITPROC] = &sys_quitproc,
+};