diff --git a/src/test/csrc/common/SimJTAG.cpp b/src/test/csrc/common/SimJTAG.cpp
index b09a4e80a..0a040f5d3 100644
--- a/src/test/csrc/common/SimJTAG.cpp
+++ b/src/test/csrc/common/SimJTAG.cpp
@@ -1,5 +1,6 @@
 // See LICENSE.SiFive for license details.
 
+#include "SimJTAG.h"
 #include "common.h"
 #include "remote_bitbang.h"
 #include <cstdlib>
@@ -11,12 +12,12 @@ remote_bitbang_t *jtag;
 bool enable_simjtag = false;
 uint16_t remote_jtag_port = 23334;
 
-extern "C" void jtag_init() {
+void jtag_init() {
   jtag = new remote_bitbang_t(remote_jtag_port);
 }
 
-extern "C" int jtag_tick(unsigned char *jtag_TCK, unsigned char *jtag_TMS, unsigned char *jtag_TDI,
-                         unsigned char *jtag_TRSTn, unsigned char jtag_TDO) {
+int jtag_tick(unsigned char *jtag_TCK, unsigned char *jtag_TMS, unsigned char *jtag_TDI, unsigned char *jtag_TRSTn,
+              unsigned char jtag_TDO) {
 #ifdef CONFIG_DIFFTEST_PERFCNT
   difftest_calls[perf_jtag_tick]++;
   difftest_bytes[perf_jtag_tick] += 5;
diff --git a/src/test/csrc/common/SimJTAG.h b/src/test/csrc/common/SimJTAG.h
new file mode 100644
index 000000000..eef7cae06
--- /dev/null
+++ b/src/test/csrc/common/SimJTAG.h
@@ -0,0 +1,25 @@
+/***************************************************************************************
+* Copyright (c) 2024 Beijing Institute of Open Source Chip (BOSC)
+* Copyright (c) 2020-2024 Institute of Computing Technology, Chinese Academy of Sciences
+*
+* DiffTest is licensed under Mulan PSL v2.
+* You can use this software according to the terms and conditions of the Mulan PSL v2.
+* You may obtain a copy of Mulan PSL v2 at:
+*          http://license.coscl.org.cn/MulanPSL2
+*
+* THIS SOFTWARE IS PROVIDED ON AN "AS IS" BASIS, WITHOUT WARRANTIES OF ANY KIND,
+* EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO NON-INFRINGEMENT,
+* MERCHANTABILITY OR FIT FOR A PARTICULAR PURPOSE.
+*
+* See the Mulan PSL v2 for more details.
+***************************************************************************************/
+
+#ifndef __SIMJTAG_H
+#define __SIMJTAG_H
+
+#include "common.h"
+
+extern "C" void jtag_init();
+extern "C" int jtag_tick(unsigned char *jtag_TCK, unsigned char *jtag_TMS, unsigned char *jtag_TDI,
+                         unsigned char *jtag_TRSTn, unsigned char jtag_TDO);
+#endif // __SIMJTAG_H
diff --git a/src/test/csrc/common/common.cpp b/src/test/csrc/common/common.cpp
index 00bf2f7e2..3277b1bed 100644
--- a/src/test/csrc/common/common.cpp
+++ b/src/test/csrc/common/common.cpp
@@ -23,7 +23,7 @@ int signal_num = 0;
 const char *emu_path = NULL;
 
 // Usage in SV/Verilog: xs_assert(`__LINE__);
-extern "C" void xs_assert(long long line) {
+void xs_assert(long long line) {
   if (assert_count >= 0) {
     printf("Assertion failed at line %lld.\n", line);
     assert_count++;
@@ -31,7 +31,7 @@ extern "C" void xs_assert(long long line) {
 }
 
 // Usage in SV/Verilog: xs_assert_v2(`__FILE__, `__LINE__);
-extern "C" void xs_assert_v2(const char *filename, long long line) {
+void xs_assert_v2(const char *filename, long long line) {
   if (assert_count >= 0) {
     printf("Assertion failed at %s:%lld.\n", filename, line);
     assert_count++;
diff --git a/src/test/csrc/common/common.h b/src/test/csrc/common/common.h
index 459443ef7..1636f112a 100644
--- a/src/test/csrc/common/common.h
+++ b/src/test/csrc/common/common.h
@@ -99,4 +99,6 @@ void common_finish();
 
 uint32_t uptime(void);
 
+extern "C" void xs_assert(long long line);
+extern "C" void xs_assert_v2(const char *filename, long long line);
 #endif // __COMMON_H
diff --git a/src/test/csrc/common/device.cpp b/src/test/csrc/common/device.cpp
index f5b84caff..3c2e81146 100644
--- a/src/test/csrc/common/device.cpp
+++ b/src/test/csrc/common/device.cpp
@@ -15,18 +15,15 @@
 ***************************************************************************************/
 
 #include "device.h"
+#include "flash.h"
+#include "sdcard.h"
+#include "uart.h"
+#include "vga.h"
 #ifdef SHOW_SCREEN
 #include <SDL2/SDL.h>
 #endif
 
 void send_key(uint8_t, bool);
-void init_sdl(void);
-
-void init_uart(void);
-void finish_uart(void);
-extern "C" void init_sd(void);
-extern "C" void finish_sd(void);
-extern "C" void init_flash(void);
 
 void init_device(void) {
 #ifdef SHOW_SCREEN
diff --git a/src/test/csrc/common/flash.cpp b/src/test/csrc/common/flash.cpp
index 7e6faa8db..5c0cab835 100644
--- a/src/test/csrc/common/flash.cpp
+++ b/src/test/csrc/common/flash.cpp
@@ -34,7 +34,7 @@ long get_flash_size() {
   return flash_bin_size;
 }
 
-extern "C" void flash_read(uint32_t addr, uint64_t *data) {
+void flash_read(uint32_t addr, uint64_t *data) {
 #ifdef CONFIG_DIFFTEST_PERFCNT
   difftest_calls[perf_flash_read]++;
   difftest_bytes[perf_flash_read] += 12;
diff --git a/src/test/csrc/common/flash.h b/src/test/csrc/common/flash.h
index bf6156da4..f569cbdaf 100644
--- a/src/test/csrc/common/flash.h
+++ b/src/test/csrc/common/flash.h
@@ -25,4 +25,5 @@ long get_flash_size();
 void init_flash(const char *flash_bin);
 void flash_finish();
 
+extern "C" void flash_read(uint32_t addr, uint64_t *data);
 #endif // __FLASH_H
diff --git a/src/test/csrc/common/golden.cpp b/src/test/csrc/common/golden.cpp
index c6433c868..0d432e34d 100644
--- a/src/test/csrc/common/golden.cpp
+++ b/src/test/csrc/common/golden.cpp
@@ -23,7 +23,7 @@
 #include "perf.h"
 #endif // CONFIG_DIFFTEST_PERFCNT
 
-extern "C" uint8_t pte_helper(uint64_t satp, uint64_t vpn, uint64_t *pte, uint8_t *level) {
+uint8_t pte_helper(uint64_t satp, uint64_t vpn, uint64_t *pte, uint8_t *level) {
 #ifdef CONFIG_DIFFTEST_PERFCNT
   difftest_calls[perf_pte_helper]++;
   difftest_bytes[perf_pte_helper] += 25;
@@ -68,7 +68,7 @@ enum {
 #define GET_LOWER32(data) ((data) & ((1UL << 32) - 1))
 #define GET_UPPER32(data) ((data) >> 32)
 
-extern "C" uint64_t amo_helper(uint8_t cmd, uint64_t addr, uint64_t wdata, uint8_t mask) {
+uint64_t amo_helper(uint8_t cmd, uint64_t addr, uint64_t wdata, uint8_t mask) {
 #ifdef CONFIG_DIFFTEST_PERFCNT
   difftest_calls[perf_amo_helper]++;
   difftest_bytes[perf_amo_helper] += 18;
diff --git a/src/test/csrc/common/golden.h b/src/test/csrc/common/golden.h
index 7d912e8d6..a4720138f 100644
--- a/src/test/csrc/common/golden.h
+++ b/src/test/csrc/common/golden.h
@@ -24,6 +24,7 @@
 
 // REF Models
 extern "C" uint8_t pte_helper(uint64_t satp, uint64_t vpn, uint64_t *pte, uint8_t *level);
+extern "C" uint64_t amo_helper(uint8_t cmd, uint64_t addr, uint64_t wdata, uint8_t mask);
 
 typedef union PageTableEntry {
   struct {
diff --git a/src/test/csrc/common/ram.cpp b/src/test/csrc/common/ram.cpp
index 140838dc4..5ff59f8ea 100644
--- a/src/test/csrc/common/ram.cpp
+++ b/src/test/csrc/common/ram.cpp
@@ -303,7 +303,7 @@ MmapMemory::~MmapMemory() {
 #endif
 }
 
-extern "C" uint64_t difftest_ram_read(uint64_t rIdx) {
+uint64_t difftest_ram_read(uint64_t rIdx) {
 #ifdef CONFIG_DIFFTEST_PERFCNT
   difftest_calls[perf_difftest_ram_read]++;
   difftest_bytes[perf_difftest_ram_read] += 8;
@@ -321,7 +321,7 @@ extern "C" uint64_t difftest_ram_read(uint64_t rIdx) {
   return rdata;
 }
 
-extern "C" void difftest_ram_write(uint64_t wIdx, uint64_t wdata, uint64_t wmask) {
+void difftest_ram_write(uint64_t wIdx, uint64_t wdata, uint64_t wmask) {
 #ifdef CONFIG_DIFFTEST_PERFCNT
   difftest_calls[perf_difftest_ram_write]++;
   difftest_bytes[perf_difftest_ram_write] += 24;
diff --git a/src/test/csrc/common/ram.h b/src/test/csrc/common/ram.h
index 78d242e85..30a3a1a9c 100644
--- a/src/test/csrc/common/ram.h
+++ b/src/test/csrc/common/ram.h
@@ -32,6 +32,8 @@
 
 uint64_t pmem_read(uint64_t raddr);
 void pmem_write(uint64_t waddr, uint64_t wdata);
+extern "C" uint64_t difftest_ram_read(uint64_t rIdx);
+extern "C" void difftest_ram_write(uint64_t wIdx, uint64_t wdata, uint64_t wmask);
 
 class InputReader {
 public:
diff --git a/src/test/csrc/common/sdcard.cpp b/src/test/csrc/common/sdcard.cpp
index 54b32dc41..4b6798cbe 100644
--- a/src/test/csrc/common/sdcard.cpp
+++ b/src/test/csrc/common/sdcard.cpp
@@ -22,8 +22,6 @@
 
 FILE *fp = NULL;
 
-extern "C" {
-
 void check_sdcard() {
   if (!fp) {
     eprintf(ANSI_COLOR_MAGENTA "[warning] sdcard img not found\n");
@@ -68,4 +66,3 @@ void finish_sd(void) {
   fclose(fp);
 #endif
 }
-}
diff --git a/src/test/csrc/common/sdcard.h b/src/test/csrc/common/sdcard.h
index dfc116c18..15407ec91 100644
--- a/src/test/csrc/common/sdcard.h
+++ b/src/test/csrc/common/sdcard.h
@@ -20,5 +20,8 @@
 #include "common.h"
 
 extern FILE *fp;
-
+extern "C" void sd_setaddr(uint32_t addr);
+extern "C" void sd_read(uint32_t *data);
+void init_sd(void);
+void finish_sd(void);
 #endif // __SDCARD_H
diff --git a/src/test/csrc/common/uart.cpp b/src/test/csrc/common/uart.cpp
index 9b1a6d35f..02f40d08e 100644
--- a/src/test/csrc/common/uart.cpp
+++ b/src/test/csrc/common/uart.cpp
@@ -14,6 +14,7 @@
 * See the Mulan PSL v2 for more details.
 ***************************************************************************************/
 
+#include "uart.h"
 #include "common.h"
 #include "stdlib.h"
 
@@ -63,7 +64,7 @@ uint8_t uart_getc() {
   return ch;
 }
 
-extern "C" void uart_getc_legacy(uint8_t *ch) {
+void uart_getc_legacy(uint8_t *ch) {
   static uint32_t lasttime = 0;
   uint32_t now = uptime();
 
diff --git a/src/test/csrc/common/uart.h b/src/test/csrc/common/uart.h
new file mode 100644
index 000000000..f9e50b360
--- /dev/null
+++ b/src/test/csrc/common/uart.h
@@ -0,0 +1,25 @@
+/***************************************************************************************
+* Copyright (c) 2024 Beijing Institute of Open Source Chip (BOSC)
+* Copyright (c) 2020-2024 Institute of Computing Technology, Chinese Academy of Sciences
+*
+* DiffTest is licensed under Mulan PSL v2.
+* You can use this software according to the terms and conditions of the Mulan PSL v2.
+* You may obtain a copy of Mulan PSL v2 at:
+*          http://license.coscl.org.cn/MulanPSL2
+*
+* THIS SOFTWARE IS PROVIDED ON AN "AS IS" BASIS, WITHOUT WARRANTIES OF ANY KIND,
+* EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO NON-INFRINGEMENT,
+* MERCHANTABILITY OR FIT FOR A PARTICULAR PURPOSE.
+*
+* See the Mulan PSL v2 for more details.
+***************************************************************************************/
+
+#ifndef __UART_H
+#define __UART_H
+
+#include "common.h"
+
+extern "C" void uart_getc_legacy(uint8_t *ch);
+void init_uart(void);
+void finish_uart(void);
+#endif // __UART_H
diff --git a/src/test/csrc/common/vga.cpp b/src/test/csrc/common/vga.cpp
index db25bfe99..4021f7bc4 100644
--- a/src/test/csrc/common/vga.cpp
+++ b/src/test/csrc/common/vga.cpp
@@ -14,8 +14,8 @@
 * See the Mulan PSL v2 for more details.
 ***************************************************************************************/
 
+#include "vga.h"
 #include "common.h"
-
 #ifdef CONFIG_DIFFTEST_PERFCNT
 #include "perf.h"
 #endif // CONFIG_DIFFTEST_PERFCNT
@@ -33,7 +33,7 @@ static SDL_Window *window;
 static SDL_Renderer *renderer;
 static SDL_Texture *texture;
 
-extern "C" void put_pixel(uint32_t pixel) {
+void put_pixel(uint32_t pixel) {
 #ifdef CONFIG_DIFFTEST_PERFCNT
   difftest_calls[perf_put_pixel]++;
   difftest_bytes[perf_put_pixel] += 4;
@@ -44,7 +44,7 @@ extern "C" void put_pixel(uint32_t pixel) {
     i = 0;
 }
 
-extern "C" void vmem_sync(void) {
+void vmem_sync(void) {
 #ifdef CONFIG_DIFFTEST_PERFCNT
   difftest_calls[perf_vmem_sync]++;
 #endif // CONFIG_DIFFTEST_PERFCNT
@@ -65,6 +65,6 @@ void finish_sdl() {
   memset(vmem, 0, sizeof(vmem));
 }
 #else
-extern "C" void put_pixel(uint32_t pixel) {}
-extern "C" void vmem_sync(void) {}
+void put_pixel(uint32_t pixel) {}
+void vmem_sync(void) {}
 #endif
diff --git a/src/test/csrc/common/vga.h b/src/test/csrc/common/vga.h
new file mode 100644
index 000000000..ed44fc6b8
--- /dev/null
+++ b/src/test/csrc/common/vga.h
@@ -0,0 +1,26 @@
+/***************************************************************************************
+* Copyright (c) 2024 Beijing Institute of Open Source Chip (BOSC)
+* Copyright (c) 2020-2024 Institute of Computing Technology, Chinese Academy of Sciences
+*
+* DiffTest is licensed under Mulan PSL v2.
+* You can use this software according to the terms and conditions of the Mulan PSL v2.
+* You may obtain a copy of Mulan PSL v2 at:
+*          http://license.coscl.org.cn/MulanPSL2
+*
+* THIS SOFTWARE IS PROVIDED ON AN "AS IS" BASIS, WITHOUT WARRANTIES OF ANY KIND,
+* EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO NON-INFRINGEMENT,
+* MERCHANTABILITY OR FIT FOR A PARTICULAR PURPOSE.
+*
+* See the Mulan PSL v2 for more details.
+***************************************************************************************/
+
+#ifndef __VGA_H
+#define __VGA_H
+
+#include "common.h"
+
+extern "C" void put_pixel(uint32_t pixel);
+extern "C" void vmem_sync(void);
+void init_sdl();
+void finish_sdl();
+#endif // __VGA_H