From 846c7aad39c0b8774b5e4d0c864f6ea88e8c8c75 Mon Sep 17 00:00:00 2001
From: TQ Hirsch <thequux@thequux.com>
Date: Thu, 28 Sep 2023 20:23:33 +0200
Subject: [PATCH] Fixed stack overflow emulation

---
 src/main/kotlin/com/thequux/mcpdp/core/CPU.kt | 26 +++++++------------
 1 file changed, 9 insertions(+), 17 deletions(-)

diff --git a/src/main/kotlin/com/thequux/mcpdp/core/CPU.kt b/src/main/kotlin/com/thequux/mcpdp/core/CPU.kt
index 259e0af..5cf91cd 100644
--- a/src/main/kotlin/com/thequux/mcpdp/core/CPU.kt
+++ b/src/main/kotlin/com/thequux/mcpdp/core/CPU.kt
@@ -933,7 +933,7 @@ class CPU(val mbus: MemBus, var tracer: ITracer = NullTracer()) {
             }
             else -> throw InvalidOpcodeException() // unreachable
         }
-        if (mode >= 1 && reg == 6) {
+        if (mode >= 1 && reg == 6 && !src) {
             checkSP(sp)
         }
         return decoded.bit(PADDR_DST_BIT, !src) bis PADDR_ARG_BIT
@@ -1186,23 +1186,15 @@ class CPU(val mbus: MemBus, var tracer: ITracer = NullTracer()) {
 
     fun checkSP(addr: UShort): UShort {
         if (cur_mode != 0) return addr
-        if (sp >= stack_limit + 256u) {
-            return addr
-        } else if (sp >= stack_limit + 224u) {
-//            if (cpu_err and CPU_ERR_STK_YLW == 0.toUShort()) {
-                logger.warn("Stack YLW")
-                // stack limit yellow
-                cpu_err = cpu_err or CPU_ERR_STK_YLW
-                setTrap(TrapReason.YEL)
-//            }
-        } else {
-//            if (cpu_err and CPU_ERR_STK_RED == 0.toUShort()) {
-                // Don't trigger if already triggered
-                logger.warn("Stack RED")
-                // we can always assume that this is running in kernel mode, as no stack check occurs in exec or user mode
-                trapRed()
+        if (sp < stack_limit + 224u || sp.toInt() and 0xFFFE == 0xFFFE) {
+            logger.warn("Stack RED")
+            trapRed()
             throw EndCycle()
-            // stack limit red
+        } else if (sp < stack_limit + 256u) {
+            logger.warn("Stack YLW")
+            // stack limit yellow
+            cpu_err = cpu_err or CPU_ERR_STK_YLW
+            setTrap(TrapReason.YEL)
         }
         return addr
     }