diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5d0720c..6f4e3f8 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -6,5 +6,7 @@ set(CMAKE_C_STANDARD 17)
 
 include(GNUInstallDirs)
 
+find_package(spdlog REQUIRED)
+
 include_directories(include)
 add_subdirectory(src)
diff --git a/difftest.toml b/difftest.toml
new file mode 100644
index 0000000..f45fd50
--- /dev/null
+++ b/difftest.toml
@@ -0,0 +1,13 @@
+# ref = "/home/xin/repo/spike-diff/build/lib/libspike-diff.so"
+# ref-prefix = "spike_"
+# dut = "/home/xin/repo/ysyx-workbench/nemu/build/riscv32-nemu-interpreter-so"
+# dut-prefix = "nemu_"
+
+ref = /home/xin/repo/ysyx-workbench/nemu/build/riscv32-nemu-interpreter-so
+ref-prefix = nemu_
+dut = "/home/xin/repo/spike-diff/build/lib/libspike-diff.so"
+dut-prefix = "spike_"
+listen = "/tmp/gdbstub-diffu.sock"
+# listen = "127.0.0.1:1234"
+memory = "/nix/store/37986mdgsqm5m8w74k0f5llzqhxgsbnv-am-kernel-riscv32-none-elf-2024-07-10/share/am-kernels/string.bin"
+# g = true
diff --git a/flake.lock b/flake.lock
index 5e5d23f..fae0e3e 100644
--- a/flake.lock
+++ b/flake.lock
@@ -112,11 +112,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1721457008,
-        "narHash": "sha256-ekpve0om5hzC1Ntd3zm1cZ9oS5pnr7a2n/tueyqFOsg=",
+        "lastModified": 1721891452,
+        "narHash": "sha256-2c9nDuXXARzoRXE67lte5kKBeFb1XmTNsvdiIbRUEgE=",
         "ref": "refs/heads/master",
-        "rev": "e7aa3319d52fa987ac2192f63aef3dcb1b057e3a",
-        "revCount": 151,
+        "rev": "de8ad578fc4fe527772cec23a7f660bde14c8570",
+        "revCount": 152,
         "type": "git",
         "url": "https://git.xinyang.life/xin/nur.git"
       },
diff --git a/flake.nix b/flake.nix
index fb8fb90..1ef76ad 100644
--- a/flake.nix
+++ b/flake.nix
@@ -38,14 +38,16 @@
             };
           };
         };
-        devShells.default = with pkgs; mkShell {
+        devShells.default = with pkgs; (mkShell.override { stdenv = ccacheStdenv; }) {
           inherit (self.checks.${system}.pre-commit-check) shellHook;
           buildInputs = self.checks.${system}.pre-commit-check.enabledPackages;
           packages = [
             clang-tools
             cmake
+            ninja
             gdb
             cli11
+            spdlog
             mini-gdbstub
           ];
         };
diff --git a/include/difftest.hpp b/include/difftest.hpp
index 7410e0e..c585844 100644
--- a/include/difftest.hpp
+++ b/include/difftest.hpp
@@ -2,13 +2,12 @@
 #define _DIFFTEST_DIFFTEST_H_
 #include "api.hpp"
 #include <filesystem>
-#include <stdexcept>
+#include <spdlog/spdlog.h>
 #include <vector>
 extern "C" {
 #include <gdbstub.h>
 }
 
-#include <iostream>
 class Difftest {
 private:
   Target dut;
@@ -55,17 +54,22 @@ public:
   arch_info_t get_arch() const { return *dut.isa_arch_info; }
 
   static bool check(Target &dut, Target &ref) {
+    size_t pcref, pcdut;
+    bool passed = true;
+    dut.ops.read_reg(dut.args.data(), 32, &pcdut);
+    ref.ops.read_reg(ref.args.data(), 32, &pcref);
     for (int r = 0; r < dut.isa_arch_info->reg_num; r++) {
       size_t regdut = 0, regref = 0;
       dut.ops.read_reg(dut.args.data(), r, &regdut);
       ref.ops.read_reg(ref.args.data(), r, &regref);
       if (regdut != regref) {
-        std::cout << "reg: " << r << " dut: " << regdut << " ref: " << regref
-                  << std::endl;
-        throw std::runtime_error("Difftest failed");
+        spdlog::error("Reg {} different: \n\tPC:\t(ref) {:x}\t(dut) {:x}\n\t"
+                      "value:\t(ref) {:x}\t(dut) {:x}",
+                      r, pcref, pcdut, regref, regdut);
+        passed = false;
       }
     }
-    return true;
+    return passed;
   };
 
   class Iterator {
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 2c13e71..6166ab9 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -1,4 +1,3 @@
 add_executable(diffu cli.cpp difftest.cpp gdbstub.cpp loader.cpp main.cpp)
-target_link_libraries(diffu PRIVATE gdbstub)
+target_link_libraries(diffu PRIVATE gdbstub spdlog::spdlog)
 install ( TARGETS diffu )
-
diff --git a/src/difftest.cpp b/src/difftest.cpp
index 8da7c30..acba918 100644
--- a/src/difftest.cpp
+++ b/src/difftest.cpp
@@ -2,10 +2,9 @@
 #include <difftest.hpp>
 #include <fstream>
 #include <gdbstub.h>
+#include <spdlog/spdlog.h>
 #include <stdexcept>
 
-#include <cstdio>
-
 Difftest::Difftest(Target &&dut, std::vector<Target> &&refs) {
   this->dut = std::move(dut);
   this->refs = std::move(refs);
@@ -36,6 +35,7 @@ void Difftest::setup(const std::filesystem::path &memory_file) {
   for (auto it = this->begin(); it != this->end(); ++it) {
     auto &target = *it;
     target.ops.init(target.args.data());
+    target.ops.write_reg(target.args.data(), 32, 0x80000000UL);
     if (target.ops.write_mem(target.args.data(), 0x80000000UL, membuf.size(),
                              membuf.data()) != 0)
       throw std::runtime_error("write_mem failed");
@@ -43,10 +43,12 @@ void Difftest::setup(const std::filesystem::path &memory_file) {
 }
 
 bool Difftest::check_all() {
+  bool passed = true;
   for (auto &ref : refs) {
-    check(dut, ref);
+    if (check(dut, ref) == false)
+      passed = false;
   }
-  return true;
+  return passed;
 }
 
 Difftest::ExecRet Difftest::exec(size_t n, gdb_action_t *ret) {
@@ -58,9 +60,12 @@ Difftest::ExecRet Difftest::exec(size_t n, gdb_action_t *ret) {
       auto &target = *it;
       *target.do_difftest = true;
       target.ops.stepi(target.args.data(), &target.last_res);
+      spdlog::trace("{} stepped once", target.meta.name);
       if (target.is_on_breakpoint()) {
         exec_ret.at_breakpoint = true;
         pbreak = &target;
+        spdlog::trace("{} on breakpoint", target.meta.name);
+        continue;
       }
       exec_ret.do_difftest = *target.do_difftest && exec_ret.do_difftest;
     }
@@ -88,7 +93,10 @@ gdb_action_t Difftest::cont() {
   while (!is_halt()) {
     exec_ret = exec(1, &ret);
     if (exec_ret.do_difftest)
-      check_all();
+      if (check_all() == false) {
+        ret.reason = gdb_action_t::ACT_BREAKPOINT;
+        break;
+      }
     if (exec_ret.at_breakpoint)
       break;
   };
@@ -122,6 +130,7 @@ int Difftest::sync_regs_to_ref(void) {
         return ret;
     }
   }
+  spdlog::trace("Applied registers value from dut to ref");
   return ret;
 }
 
diff --git a/src/gdbstub.cpp b/src/gdbstub.cpp
index 6d613bb..e5774f2 100644
--- a/src/gdbstub.cpp
+++ b/src/gdbstub.cpp
@@ -2,10 +2,10 @@
 #include <CLI/Error.hpp>
 #include <cstring>
 #include <difftest.hpp>
+#include <spdlog/spdlog.h>
 #include <sstream>
 extern "C" {
 #include <gdbstub.h>
-}
 
 static void difftest_cont(void *args, gdb_action_t *res) {
   Difftest *diff = (Difftest *)args;
@@ -65,6 +65,7 @@ std::vector<std::string> split_into_args(const std::string &command) {
 
 static char *gdbstub_monitor(void *args, const char *s) {
   Difftest *diff = (Difftest *)args;
+  spdlog::trace("monitor");
   CLI::App parser;
   std::string ret = "";
 
@@ -110,6 +111,7 @@ static char *gdbstub_monitor(void *args, const char *s) {
     return strdup(ret_stream.str().c_str());
   }
 }
+}
 
 int gdbstub_loop(Difftest *diff, std::string socket_addr) {
   target_ops gdbstub_ops = {.cont = difftest_cont,
@@ -124,14 +126,16 @@ int gdbstub_loop(Difftest *diff, std::string socket_addr) {
                             .monitor = gdbstub_monitor};
   gdbstub_t gdbstub_priv;
 
-  std::cout << "Waiting for gdb connection at " << socket_addr << std::endl;
+  arch_info_t arch = diff->get_arch();
 
-  if (!gdbstub_init(&gdbstub_priv, &gdbstub_ops, diff->get_arch(),
+  if (!gdbstub_init(&gdbstub_priv, &gdbstub_ops, arch, nullptr,
                     socket_addr.c_str())) {
-    std::cerr << "Failed to init socket at: " << socket_addr << std::endl;
+    spdlog::error("Failed to init socket at: {}", socket_addr);
     return false;
   }
 
+  spdlog::info("Connected to gdb at {}", socket_addr);
+
   bool success = gdbstub_run(&gdbstub_priv, diff);
   gdbstub_close(&gdbstub_priv);
   return !success;
diff --git a/src/loader.cpp b/src/loader.cpp
index fa5b062..b7f8413 100644
--- a/src/loader.cpp
+++ b/src/loader.cpp
@@ -1,7 +1,7 @@
 #include "api.hpp"
-#include <cstdint>
 #include <dlfcn.h>
 #include <gdbstub.h>
+#include <spdlog/spdlog.h>
 #include <stdexcept>
 
 Target::Target(const std::string &name, const std::string &func_prefix,
@@ -11,16 +11,19 @@ Target::Target(const std::string &name, const std::string &func_prefix,
           .libpath = path,
           .dlhandle = dlopen(path.c_str(), RTLD_NOW)};
 
+  spdlog::info("Library handle: {}", meta.dlhandle);
   if (!meta.dlhandle) {
     throw std::runtime_error(dlerror());
   }
 
 #define LOAD_SYMBOL(ops, handle, prefix, name)                                 \
   do {                                                                         \
+    std::string symbol_name = func_prefix + #name;                             \
     (ops).name = reinterpret_cast<decltype((ops).name)>(                       \
-        dlsym((handle), ((prefix) + #name).c_str()));                          \
+        dlsym((handle), symbol_name.c_str()));                                 \
     if (!((ops).name))                                                         \
       goto load_error;                                                         \
+    spdlog::debug("Found {} at {}", symbol_name, ((void *)((ops).name)));      \
   } while (0);
 
   LOAD_SYMBOL(ops, meta.dlhandle, func_prefix, cont);
diff --git a/src/main.cpp b/src/main.cpp
index 7b1110d..29d209f 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1,10 +1,12 @@
 #include "api.hpp"
 #include "config.hpp"
 #include "difftest.hpp"
+#include <spdlog/cfg/env.h>
 
 int gdbstub_loop(Difftest *, std::string);
 
 int main(int argc, char **argv) {
+  spdlog::cfg::load_env_levels();
   Config config;
   int ret = 0;
   ret = config.cli_parse(argc, argv);