difftest: fix REF_SO path

Makefile

@@ -56,8 +56,12 @@ $(EMU_MK): $(SIM_TOP_V) | $(EMU_DEPS)
 	verilator --cc --exe $(VERILATOR_FLAGS) \
 		-o $(abspath $(EMU)) -Mdir $(@D) $^ $(EMU_DEPS)
 
-$(EMU): $(EMU_MK) $(EMU_DEPS) $(EMU_HEADERS)
-	$(MAKE) -C $(dir $(EMU_MK)) -f $(abspath $(EMU_MK))
+REF_SO := $(NEMU_HOME)/build/riscv32-nemu-so
+$(REF_SO):
+	$(MAKE) -C $(NEMU_HOME) ISA=riscv32 SHARE=1
+
+$(EMU): $(EMU_MK) $(EMU_DEPS) $(EMU_HEADERS) $(REF_SO)
+	CPPFLAGS=-DREF_SO=\\\"$(REF_SO)\\\" $(MAKE) -C $(dir $(EMU_MK)) -f $(abspath $(EMU_MK))
 
 ifdef mainargs
 MAINARGS = -a $(mainargs)

src/test/csrc/difftest.cpp

@@ -4,7 +4,9 @@
 #include <stdlib.h>
 #include <dlfcn.h>
 
-#define REF_SO "/home/yzh/projectn/nemu/build/riscv32-nemu-so"
+#ifndef REF_SO
+# error Please define REF_SO to the path of NEMU shared object file
+#endif
 
 void (*ref_difftest_memcpy_from_dut)(paddr_t dest, void *src, size_t n) = NULL;
 void (*ref_difftest_getregs)(void *c) = NULL;