wrote a shell but have an error will debug tomorrow

common.h

@@ -20,6 +20,8 @@ typedef uint32_t vaddr_t;
 #define va_end    __builtin_va_end
 #define va_arg    __builtin_va_arg
 #define PAGE_SIZE 4096
+#define SYS_PUTCHAR 1
+#define SYS_GETCHAR 2
 
 void *memset(void *buf, char c, size_t n);
 void *memcpy(void *dst, const void *src, size_t n);