From 2abd66ea0ca1c89a9bd928196f74c435a11a123b Mon Sep 17 00:00:00 2001
From: Sidney Cadot <sidney@jigsaw.nl>
Date: Sat, 30 Nov 2024 12:36:35 +0100
Subject: [PATCH] Fixed the behavior of the JMP (ind) instruction in sim65 when
 it runs with the "6502X" CPU type.

The JMP (ind) bug is present in the 6502 which is emulated by both the "6502" and "6502X"
emulation targets of sim65; specifically, the OPC_6502_6C handler. In the old code, the
bug-exhibiting code was not executed when the target was set to 6502X, which is incorrect.
the patch removes the (CPU == CPU_6502) check, which made no sense.

The JMP (ind) bug was actually fixed in the 65c02. Indeed, the OPC_65C02_6C opcode handler
has code that implements the 'right' behavior.
---
 src/sim65/6502.c | 26 +++++++++-----------------
 1 file changed, 9 insertions(+), 17 deletions(-)

diff --git a/src/sim65/6502.c b/src/sim65/6502.c
index 448e81669..3f912b27e 100644
--- a/src/sim65/6502.c
+++ b/src/sim65/6502.c
@@ -1964,25 +1964,17 @@ static void OPC_6502_6C (void)
     PC = Regs.PC;
     Lo = MemReadWord (PC+1);
 
-    if (CPU == CPU_6502)
-    {
-         /* Emulate the 6502 bug */
-        Cycles = 5;
-        Regs.PC = MemReadByte (Lo);
-        Hi = (Lo & 0xFF00) | ((Lo + 1) & 0xFF);
-        Regs.PC |= (MemReadByte (Hi) << 8);
+    /* Emulate the buggy 6502 behavior */
+    Cycles = 5;
+    Regs.PC = MemReadByte (Lo);
+    Hi = (Lo & 0xFF00) | ((Lo + 1) & 0xFF);
+    Regs.PC |= (MemReadByte (Hi) << 8);
 
-        /* Output a warning if the bug is triggered */
-        if (Hi != Lo + 1)
-        {
-            Warning ("6502 indirect jump bug triggered at $%04X, ind addr = $%04X",
-                     PC, Lo);
-        }
-    }
-    else
+    /* Output a warning if the bug is triggered */
+    if (Hi != Lo + 1)
     {
-        Cycles = 6;
-        Regs.PC = MemReadWord(Lo);
+        Warning ("6502 indirect jump bug triggered at $%04X, ind addr = $%04X",
+                    PC, Lo);
     }
 
     ParaVirtHooks (&Regs);