update

.gitignore

@@ -1 +1,2 @@
 **/build
+**/.cache

instrument/CMakeLists.txt

@@ -0,0 +1,8 @@
+cmake_minimum_required(VERSION 3.5)
+project(interceptor)
+
+set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
+
+add_subdirectory(target)
+add_subdirectory(instrument)
+add_subdirectory(app)

instrument/app/CMakeLists.txt

@@ -0,0 +1,6 @@
+cmake_minimum_required(VERSION 3.5)
+project(app)
+
+file(GLOB SOURCES "src/*.cpp")
+add_executable(${PROJECT_NAME} ${SOURCES})
+target_link_libraries(${PROJECT_NAME} PRIVATE target)

instrument/app/src/main.cpp

@@ -0,0 +1,7 @@
+#include "A.h"
+
+int main(int argc, const char *argp[], const char *envp[]) {
+	A a;
+	a.method("test");
+	return 0;
+}

instrument/compile_commands.json

@@ -0,0 +1 @@
+build/compile_commands.json

instrument/instrument/CMakeLists.txt

@@ -0,0 +1,10 @@
+cmake_minimum_required(VERSION 3.5)
+project(instrument)
+
+file(GLOB SOURCES "src/*.cpp")
+add_library(${PROJECT_NAME} SHARED ${SOURCES})
+add_dependencies(${PROJECT_NAME} target)
+target_link_libraries(${PROJECT_NAME} 
+	PRIVATE 
+	dl
+)

instrument/instrument/src/intercept.cpp

@@ -0,0 +1,31 @@
+#include <dlfcn.h>
+#include <string>
+#include <iostream>
+using std::cout;
+using std::endl;
+
+class A;
+
+// Function pointer to store the original method
+typedef void (*MethodType)(A *, const std::string &);
+MethodType original_method = nullptr;
+
+extern "C" void _ZN1A6methodERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE(A *obj, const std::string &msg) {
+    cout << "Intercepted A::method with message: " << msg << endl;
+
+    // Call the original method if it was found
+    if (original_method) {
+        original_method(obj, msg);
+    }
+}
+
+// Initialization function
+extern "C" void __attribute__((constructor)) init() {
+    cout << "Shared library has been preloaded." << endl;
+
+    // Get the original A::method using dlsym and RTLD_NEXT
+    original_method = (MethodType)dlsym(RTLD_NEXT, "_ZN1A6methodERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE");
+    if (!original_method) {
+        cout << "Error: unable to find original A::method" << endl;
+    }
+}

instrument/target/CMakeLists.txt

@@ -0,0 +1,8 @@
+cmake_minimum_required(VERSION 3.5)
+project(target)
+
+file(GLOB SOURCES "src/*.cpp")
+add_library(${PROJECT_NAME} SHARED ${SOURCES})
+target_include_directories(${PROJECT_NAME} 
+	PUBLIC
+	include)

instrument/target/include/A.h

@@ -0,0 +1,7 @@
+#pragma once
+#include <string>
+
+class A {
+public:
+    void method(const std::string& msg);
+};

instrument/target/src/A.cpp

@@ -0,0 +1,8 @@
+#include "A.h"
+#include <iostream>
+using std::cout;
+using std::endl;
+
+void A::method(const std::string &msg) {
+	cout << "original: " << msg << endl;
+}