diff --git a/Makefile b/Makefile
index 7a178c9..dd329ef 100644
--- a/Makefile
+++ b/Makefile
@@ -1,10 +1,17 @@
 
 TEST_OBJS = $(addsuffix .o,$(basename $(wildcard tests/*.S)))
 FIRMWARE_OBJS = firmware/start.o firmware/irq.o firmware/print.o firmware/sieve.o firmware/multest.o firmware/stats.o
+GCC_WARNS = -Wall -Wextra -Wshadow -Wundef
 
 test: testbench.exe firmware/firmware.hex
 	vvp -N testbench.exe
 
+testbench.vcd: testbench.exe firmware/firmware.hex
+	vvp -N $< +vcd
+
+testbench_view: testbench.vcd
+	gtkwave $< testbench.gtkw
+
 test_sp: testbench_sp.exe firmware/firmware.hex
 	vvp -N testbench_sp.exe
 
@@ -50,7 +57,7 @@ firmware/start.o: firmware/start.S
 	riscv64-unknown-elf-gcc -c -m32 -o $@ $<
 
 firmware/%.o: firmware/%.c
-	riscv64-unknown-elf-gcc -c -m32 -march=RV32I -Os -ffreestanding -nostdlib -o $@ $<
+	riscv64-unknown-elf-gcc -c -m32 -march=RV32I -Os $(GCC_WARNS) -ffreestanding -nostdlib -o $@ $<
 
 tests/%.o: tests/%.S tests/riscv_test.h tests/test_macros.h
 	riscv64-unknown-elf-gcc -c -m32 -o $@ -DTEST_FUNC_NAME=$(notdir $(basename $<)) \
@@ -62,7 +69,7 @@ toc:
 clean:
 	rm -vrf $(FIRMWARE_OBJS) $(TEST_OBJS) \
 		firmware/firmware.{elf,bin,hex,map} synth.v \
-		testbench{,_sp,_axi,_synth}.exe testbench.vcd
+		testbench.exe testbench_sp.exe testbench_axi.exe testbench_synth.exe testbench.vcd
 
 .PHONY: test test_sp test_axi test_sync toc clean
 
diff --git a/testbench.v b/testbench.v
index 53badd3..3a1c119 100644
--- a/testbench.v
+++ b/testbench.v
@@ -237,8 +237,10 @@ module testbench;
 	end
 
 	initial begin
-		$dumpfile("testbench.vcd");
-		$dumpvars(0, testbench);
+		if ($test$plusargs("vcd")) begin
+			$dumpfile("testbench.vcd");
+			$dumpvars(0, testbench);
+		end
 		repeat (1000000) @(posedge clk);
 		$display("TIMEOUT");
 		$finish;