GP-1487: Adding better explanation for pcode UNIMPLEMENTED.

Ghidra/Debug/Framework-TraceModeling/src/test/java/ghidra/pcode/exec/trace/TracePcodeEmulatorTest.java

@@ -900,4 +900,27 @@ public class TracePcodeEmulatorTest extends AbstractGhidraHeadlessIntegrationTes
 				TraceSleighUtils.evaluate("RCX", tb.trace, 1, thread, 0));
 		}
 	}
+
+	/**
+	 * Test that unimplemented instructions (as opposed to instructions with no semantics) result in
+	 * an interrupt.
+	 */
+	@Test(expected = PcodeExecutionException.class)
+	public void testUNIMPL() throws Throwable {
+		try (ToyDBTraceBuilder tb = new ToyDBTraceBuilder("Test", "Toy:BE:64:default")) {
+			assertEquals(Register.NO_CONTEXT, tb.language.getContextBaseRegister());
+
+			TraceThread thread = initTrace(tb,
+				List.of(
+					"pc = 0x00400000;",
+					"sp = 0x00110000;"),
+				List.of(
+					"unimpl"));
+
+			TracePcodeEmulator emu = new TracePcodeEmulator(tb.trace, 0);
+			PcodeThread<byte[]> emuThread = emu.newThread(thread.getPath());
+			emuThread.overrideContextWithDefault();
+			emuThread.stepInstruction();
+		}
+	}
 }

Ghidra/Debug/ProposedUtils/src/main/java/ghidra/pcode/exec/PcodeExecutor.java

@@ -122,10 +122,22 @@ public class PcodeExecutor<T> {
 		}
 	}
 
+	protected void badOp(PcodeOp op) {
+		switch (op.getOpcode()) {
+			case PcodeOp.UNIMPLEMENTED:
+				throw new LowlevelError(
+					"Encountered an unimplemented instruction at " + op.getSeqnum().getTarget());
+			default:
+				throw new LowlevelError(
+					"Unsupported p-code op at " + op.getSeqnum().getTarget() + ": " + op);
+		}
+	}
+
 	public void stepOp(PcodeOp op, PcodeFrame frame, SleighUseropLibrary<T> library) {
 		OpBehavior b = OpBehaviorFactory.getOpBehavior(op.getOpcode());
 		if (b == null) {
-			throw new LowlevelError("Unsupported pcode op" + op);
+			badOp(op);
+			return;
 		}
 		if (b instanceof UnaryOpBehavior) {
 			executeUnaryOp(op, (UnaryOpBehavior) b);
@@ -164,7 +176,8 @@ public class PcodeExecutor<T> {
 				executeReturn(op, frame);
 				return;
 			default:
-				throw new LowlevelError("Unsupported op " + op);
+				badOp(op);
+				return;
 		}
 	}
 

Ghidra/Processors/Toy/data/languages/toyInstructions.sinc

@@ -61,6 +61,7 @@
 #  1010 0100 ssss tttt  # user_four rs rt   user_four rs rt       
 #  1010 0101 nnnn nnnn  # user_five n       user_five n  
 #  1010 0110 ssss 0000  # user_six rs       user_six rs
+#  1010 1000 0000 0000  # unimpl
 #
 #### RESERVED
 #  1101 1001 xxxx xxxx  # RESERVED BANK
@@ -222,3 +223,4 @@ define pcodeop pcodeop_three;
 :user_five Rel8 is $(INSTR_PHASE) op1215=0xa & op0811=0x05 & Rel8                  { lr = inst_next; call Rel8; pcodeop_three();} 
 :user_six rs is $(INSTR_PHASE) op1215=0xa & op0811=0x06 & rs & op0003=0x0          { r1 = pcodeop_one(rs); call [r1];}
 
+:unimpl is $(INSTR_PHASE) op1215=0xa & op0811=0x08 & op0007=0 unimpl