rename die to panic, add exit function

lang/src/main.asm

@@ -4,8 +4,8 @@
 section .data
     hello_msg db "Hello, World!", 10
     hello_msg_len equ $ - hello_msg
-    die_msg db "panic occured!", 10
-    die_msg_len equ $ - die_msg
+    panic_msg db "panic occured!", 10
+    panic_msg_len equ $ - panic_msg
     file_error_msg db "Could not open file: "
     file_error_msg_len equ $ - file_error_msg
     error_msg db "Error: "
@@ -32,22 +32,27 @@ _start:
     call fopen_read
     mov rax, 42
     ; exit with success
-    mov rdi, 0           ; status:
-    mov rax, 60          ; syscall: exit
-    syscall
+    mov rdx, 0
+    call exit
 
 .no_filename:
-    call die
+    call panic
 
-die:
-    mov rdx, die_msg
-    mov rcx, die_msg_len
+panic:
+    mov rdx, panic_msg
+    mov rcx, panic_msg_len
     call eprint_str
     ; exit with error code 1
     mov rax, 60          ; syscall: exit
     mov rdi, 1           ; status: 1
     syscall
-    ret                         ; should never reach here
+
+;; abort the program
+;; rdx: status code
+exit:
+    mov rax, 60          ; syscall: exit
+    mov rdi, rdx
+    syscall
 
 ;; ==============================
 ;; Helper functions