From e8c28c2a847a0fb15e37d4b1c1dbf67a01d701cb Mon Sep 17 00:00:00 2001
From: Dan <46821332+nsadeveloper789@users.noreply.github.com>
Date: Wed, 25 Sep 2024 09:57:49 -0400
Subject: [PATCH] GP-4967: Corrected issues related to emulator cached block
 instruction re-use.

---
 .../pcode/emu/SleighInstructionDecoder.java   | 39 +++++++++++++------
 .../AbstractBytesPcodeExecutorStatePiece.java |  6 +--
 2 files changed, 31 insertions(+), 14 deletions(-)

diff --git a/Ghidra/Framework/Emulation/src/main/java/ghidra/pcode/emu/SleighInstructionDecoder.java b/Ghidra/Framework/Emulation/src/main/java/ghidra/pcode/emu/SleighInstructionDecoder.java
index 2271de0860..621092668a 100644
--- a/Ghidra/Framework/Emulation/src/main/java/ghidra/pcode/emu/SleighInstructionDecoder.java
+++ b/Ghidra/Framework/Emulation/src/main/java/ghidra/pcode/emu/SleighInstructionDecoder.java
@@ -15,6 +15,8 @@
  */
 package ghidra.pcode.emu;
 
+import java.util.Objects;
+
 import ghidra.app.util.PseudoInstruction;
 import ghidra.pcode.emulate.InstructionDecodeException;
 import ghidra.pcode.exec.DecodePcodeExecutionException;
@@ -73,14 +75,18 @@ public class SleighInstructionDecoder implements InstructionDecoder {
 			Disassembler.getDisassembler(language, addrFactory, TaskMonitor.DUMMY, listener);
 	}
 
-	@Override
-	public Instruction decodeInstruction(Address address, RegisterValue context) {
-		lastMsg = DEFAULT_ERROR;
-		if (block != null &&
-			(instruction = (PseudoInstruction) block.getInstructionAt(address)) != null) {
-			return instruction;
+	protected boolean useCachedInstruction(Address address, RegisterValue context) {
+		if (block == null) {
+			return false;
 		}
-		/*
+		// Always use instruction within last block decoded assuming we flowed from another
+		// instruction within the same block.  The block should be null is starting a new flow.
+		instruction = (PseudoInstruction) block.getInstructionAt(address);
+		return instruction != null;
+	}
+
+	protected void parseNewBlock(Address address, RegisterValue context) {
+		/**
 		 * Parse as few instructions as possible. If more are returned, it's because they form a
 		 * parallel instruction group. In that case, I should not have to worry self-modifying code
 		 * within that group, so no need to re-disassemble after each is executed.
@@ -91,17 +97,28 @@ public class SleighInstructionDecoder implements InstructionDecoder {
 			throw new DecodePcodeExecutionException(lastMsg, address);
 		}
 		instruction = (PseudoInstruction) block.getInstructionAt(address);
+	}
+
+	@Override
+	public Instruction decodeInstruction(Address address, RegisterValue context) {
+		lastMsg = DEFAULT_ERROR;
+		if (!useCachedInstruction(address, context)) {
+			parseNewBlock(address, context);
+		}
 		lengthWithDelays = computeLength();
 		return instruction;
 	}
 
 	@Override
 	public void branched(Address address) {
-		/*
-		 * This shouldn't happen in the middle of a parallel instruction group, but in case the
-		 * group modifies itself and jumps back to itself, this will ensure it is re-disassembled.
+		/**
+		 * There may be internal branching within a decoded block. Those shouldn't clear the block.
+		 * However, if the cached instruction's context does not match the desired one, assume we're
+		 * starting a new block. That check will have to wait for the decode call, though.
 		 */
-		block = null;
+		if (block.getInstructionAt(address) == null) {
+			block = null;
+		}
 	}
 
 	/**
diff --git a/Ghidra/Framework/Emulation/src/main/java/ghidra/pcode/exec/AbstractBytesPcodeExecutorStatePiece.java b/Ghidra/Framework/Emulation/src/main/java/ghidra/pcode/exec/AbstractBytesPcodeExecutorStatePiece.java
index 576aff6abd..32ba5a4acd 100644
--- a/Ghidra/Framework/Emulation/src/main/java/ghidra/pcode/exec/AbstractBytesPcodeExecutorStatePiece.java
+++ b/Ghidra/Framework/Emulation/src/main/java/ghidra/pcode/exec/AbstractBytesPcodeExecutorStatePiece.java
@@ -4,9 +4,9 @@
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
- * 
+ *
  *      http://www.apache.org/licenses/LICENSE-2.0
- * 
+ *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
@@ -66,7 +66,7 @@ public abstract class AbstractBytesPcodeExecutorStatePiece<S extends BytesPcodeE
 
 		@Override
 		public Memory getMemory() {
-			throw new UnsupportedOperationException();
+			return null;
 		}
 
 		@Override