User mode

src/user.c

@@ -0,0 +1,18 @@
+#include "user.h"
+
+extern char __stack_top[];
+
+__attribute__((noreturn)) void exit(void) {
+    for (;;)
+        ;
+}
+
+void putchar(char c) { /* Доделать*/ }
+
+__attribute__((section(".text.start"))) __attribute__((naked)) void
+start(void) {
+    __asm__ __volatile__(
+        "mv sp, %[stack_top] \n"
+        "call main           \n"
+        "call exit           \n" ::[stack_top] "r"(__stack_top));
+}