From 09750b7388145961d8c457ca23dfcb8ca7914e3c Mon Sep 17 00:00:00 2001
From: Yi-Ting Shih <ytshih@it.cs.nycu.edu.tw>
Date: Mon, 6 Apr 2026 22:05:23 +0800
Subject: [PATCH] Fix: wtf is size <0

---
 code/userprog/ksyscall.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/code/userprog/ksyscall.h b/code/userprog/ksyscall.h
index 68718f1..afe38e8 100755
--- a/code/userprog/ksyscall.h
+++ b/code/userprog/ksyscall.h
@@ -53,6 +53,8 @@ OpenFileId SysOpen(char *name) {
 }
 
 int SysWrite(char *buffer, int size, OpenFileId id) {
+  if (size < 0)  // Invalid size
+    return -1;
   if (id == 1) {  // Console output (stdout)
     for (int i = 0; i < size; i++)
       kernel->synchConsoleOut->PutChar(buffer[i]);
@@ -65,6 +67,8 @@ int SysWrite(char *buffer, int size, OpenFileId id) {
 }
 
 int SysRead(char *buffer, int size, OpenFileId id) {
+  if (size < 0)  // Invalid size
+    return -1;
   if (id == 0) {  // Console input (stdin)
     for (int i = 0; i < size; i++)
       buffer[i] = kernel->synchConsoleIn->GetChar();