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Add base project.
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‎.github/workflows/ci.yml

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name: Test
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on:
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push:
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pull_request:
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workflow_dispatch:
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jobs:
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test:
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name: Tests for MetaCall
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strategy:
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fail-fast: false
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matrix:
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build: [Debug, Release]
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os: [macos-13, macos-14, macos-15, ubuntu-22.04, ubuntu-24.04, windows-2019, windows-2022, windows-2025]
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runs-on: ${{ matrix.os }}
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steps:
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- uses: actions/checkout@v4
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- name: Build Project
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uses: threeal/[email protected]
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with:
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build-dir: build
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options: |
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CMAKE_BUILD_TYPE=${{ matrix.build }}
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- name: Run Tests
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shell: bash
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run: |
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cd build
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ctest -VV -C ${{ matrix.build }}

‎.gitignore

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build
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.vscode
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.cache

‎CMakeLists.txt

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cmake_minimum_required(VERSION 3.10)
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project(MetaCallPoC VERSION 1.0)
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set(CMAKE_C_STANDARD 99)
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set(CMAKE_CXX_STANDARD 11)
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set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
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# Default build type
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if(NOT CMAKE_BUILD_TYPE)
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set(CMAKE_BUILD_TYPE "Debug")
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endif()
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# Debug
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if("${CMAKE_BUILD_TYPE}" STREQUAL "Debug")
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if(WIN32)
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add_compile_options(/fsanitize=address)
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else()
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add_compile_options(-fsanitize=address)
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add_compile_options(-fsanitize=undefined)
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add_link_options(-fsanitize=address)
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add_link_options(-fsanitize=undefined)
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endif()
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endif()
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# Test
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include(CTest)
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# Windows exports
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if(WIN32)
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set(CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS ON)
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endif()
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# PLTHook
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include(FetchContent)
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set(PLTHook_SOURCE_DIR "${CMAKE_CURRENT_BINARY_DIR}/plthook")
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FetchContent_Declare(PLTHook
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GIT_REPOSITORY https://github.com/metacall/plthook.git
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GIT_TAG master
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SOURCE_DIR ${PLTHook_SOURCE_DIR}
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)
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FetchContent_MakeAvailable(PLTHook)
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set(PLTHook_INCLUDE_DIR "${PLTHook_SOURCE_DIR}")
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if(APPLE)
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set(PLTHOOK_SOURCE "${PLTHook_SOURCE_DIR}/plthook_osx.c")
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elseif(WIN32 OR MINGW)
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set(PLTHOOK_SOURCE "${PLTHook_SOURCE_DIR}/plthook_win32.c")
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else()
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set(PLTHOOK_SOURCE "${PLTHook_SOURCE_DIR}/plthook_elf.c")
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endif()
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# MetaCall Library
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add_library(metacall SHARED source/metacall.c ${PLTHOOK_SOURCE})
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target_include_directories(metacall PRIVATE ${PLTHook_INCLUDE_DIR})
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target_link_libraries(metacall ${CMAKE_DL_LIBS})
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# NodeJS library of NodeJS static
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add_library(libnode-static source/libnode.c)
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target_compile_definitions(libnode-static PUBLIC NODE_STATIC=1) # Add definition for compiling as "node-static"
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# NodeJS static
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add_executable(node-static source/node-static.c)
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target_link_libraries(node-static libnode-static ${CMAKE_DL_LIBS} metacall)
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set_property(TARGET node-static PROPERTY ENABLE_EXPORTS ON) # Required to export the symbols on the executable
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add_test(NAME node-static
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COMMAND $<TARGET_FILE:node-static>
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)
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# NodeJS library of NodeJS dynamic
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add_library(libnode SHARED source/libnode.c)
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# NodeJS dynamic
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add_executable(node-dynamic source/node-dynamic.c)
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target_link_libraries(node-dynamic ${CMAKE_DL_LIBS} metacall)
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add_test(NAME node-dynamic
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COMMAND $<TARGET_FILE:node-dynamic>
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)
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# Normal Executable
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add_executable(normal-executable source/normal-executable.c)
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target_link_libraries(normal-executable ${CMAKE_DL_LIBS} metacall)
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add_test(NAME normal-executable
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COMMAND $<TARGET_FILE:normal-executable>
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)
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set_property(TEST normal-executable PROPERTY ENVIRONMENT "NORMAL_EXECUTABLE=1")
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# NodeJS Loader is linked weakly to libnode2
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add_library(node_loader SHARED source/node_loader.c)
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target_link_libraries(node_loader
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PRIVATE
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# Delay load for MSVC
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$<$<CXX_COMPILER_ID:MSVC>:libnode2>
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$<$<CXX_COMPILER_ID:MSVC>:delayimp>
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)
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target_link_options(node_loader
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PRIVATE
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# TODO: Add flags for gcc?
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$<$<AND:$<BOOL:${APPLE}>,$<CXX_COMPILER_ID:AppleClang,Clang>>:-Wl,-undefined,dynamic_lookup>
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$<$<CXX_COMPILER_ID:MSVC>:/DELAYLOAD:$<TARGET_FILE_BASE_NAME:libnode2>.dll>
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)
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# NodeJS library of NodeJS Loader
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add_library(libnode2 SHARED source/libnode2.c source/libnode2.cpp)
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# Additional dlinfo test (unrelated to the PoC)
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if(NOT WIN32 AND NOT APPLE)
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add_executable(dlinfo-test source/dlinfo-test.c)
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target_link_libraries(dlinfo-test ${CMAKE_DL_LIBS})
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endif()

‎README.md

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# plthook-poc
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# MetaCall PLT/IAT Hooking Proof of Concept
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Proof of Concept for implementing PLT/IAT hooking for MetaCall.
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This will be used in order to allow MetaCall to be loaded in places where a runtime is already started.
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The feature once implemented will solve the following isuses:
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- https://github.com/metacall/core/issues/231
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- https://github.com/metacall/core/issues/460
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- https://github.com/metacall/core/issues/493
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- https://github.com/metacall/core/issues/31
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## How it works
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First of all we have the following preconditions:
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- `libmetacall` which loads `libnode_loader`.
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- `libnode_loader` is not linked to anything but we are going to weakly link it to `libnode`, this means that in Windows it must be linked with `/DELAYLOAD`, in Linux and MacOS it must not be linked.
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There are two possible cases, this happens before loading libnode_loader:
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- MetaCall is not being executed by `node.exe`, then:
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1) Windows:
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- `libmetacall` loads dynamically all the dependencies of `libnode_loader` (aka `libnode`).
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- We list all the symbols of each dependency (aka `libnode`) so we construct a hashmap of symbol string to symbol function pointer.
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- We list all the unresolved symbols of `libnode_loader` and we link them to `libnode`.
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2) MacOS & Linux:
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- `libmetacall` loads dynamically all the dependencies of `libnode_loader` (aka `libnode`).
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- Linking is resolved by the linker automatically.
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- MetaCall is being executed by node.exe, then we have two possible cases:
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1) `node.exe` compiled statically (without `libnode`):
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- We get all the library dependencies from `node.exe` and we do not find `libnode`, so we get the handle of the currrent process.
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- We list all symbols of `node.exe` and we construct a hash map a hashmap of symbol string to symbol function pointer.
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- We list all the unresolved symbols of `libnode_loader` and we link them to `node.exe`.
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2) `node.exe` compiled dynamically (with `libnode`):
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- We get all the library dependencies from `node.exe` and we find `libnode` so we get the handle from it.
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- We list all the symbols of each dependency (aka `libnode`) so we construct a hashmap of symbol string to symbol function pointer of those dependencies (`libnode`).
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- We list all the unresolved symbols of `libnode_loader` and we link them to `libnode` of `node.exe`.
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## Outcome
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With this methodology we prevent loading a library that contains a runtime. This is very dangerous because numerous runtimes rely on constructors (C++ constructors of static class delacarations or C compiler dependant constructor mechanisms like GNU or Clang `__attribute__((destructor))`) that are mutually exclusive between them. So if we only load the library but we do not call method of the library, it can still cause errors.
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The loaders will be redirected to the proper runtime, reusing the functions and instance of the already running runtime.

‎source/dlinfo-test.c

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#include <stdio.h>
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#ifndef __USE_GNU
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#define __USE_GNU
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#endif
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#include <dlfcn.h>
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#include <link.h>
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int main() {
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// Open a shared library
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const char *lib_name = "./liblibnode.so"; // For example, the math library
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void *handle = dlopen(lib_name, RTLD_NOW);
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if (!handle) {
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fprintf(stderr, "Error opening library %s: %s\n", lib_name, dlerror());
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return 1;
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}
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// Retrieve the dynamic link map of the shared object using dlinfo
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struct link_map *map;
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if (dlinfo(handle, RTLD_DI_LINKMAP, &map) == 0) {
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printf("Link map of %s:\n", lib_name);
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while (map) {
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printf(" Name: %s, Address: %ld\n", map->l_name, map->l_addr);
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map = map->l_next;
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}
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} else {
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fprintf(stderr, "dlinfo failed: %s\n", dlerror());
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}
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// Use dlsym to find a symbol in the library (e.g., "sin" in libm.so)
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void *symbol = dlsym(handle, "sin");
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if (symbol) {
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printf("Found symbol 'sin' at address: %p\n", symbol);
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} else {
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printf("Symbol 'sin' not found: %s\n", dlerror());
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}
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// Close the library handle
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dlclose(handle);
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return 0;
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}

‎source/dynlib.h

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#ifndef DYNLYB
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#define DYNLYB 1
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#include <stdio.h>
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#include <assert.h>
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#if defined(WIN32) || defined(_WIN32)
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#include <windows.h>
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typedef HMODULE dyn_handle_t;
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#define DYN_LIBRARY(lib) lib ".dll"
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#define RTLD_LAZY 0 // Use this as workaround
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#define RTLD_GLOBAL 0
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#else
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#ifndef __USE_GNU
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#define __USE_GNU // This is required for dlinfo and dladdr
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#endif
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#include <dlfcn.h>
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typedef void* dyn_handle_t;
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#ifdef __APPLE__
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#define DYN_LIBRARY(lib) "lib" lib ".dylib"
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#else
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#define DYN_LIBRARY(lib) "lib" lib ".so"
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#include <link.h>
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#endif
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#endif
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#define DYN_LIBRARY_PATH(path, lib) path DYN_LIBRARY(lib)
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static inline int dyn_open(char *lib, int flags, dyn_handle_t *handle) {
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#if defined(WIN32) || defined(_WIN32)
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*handle = LoadLibrary(lib);
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if (*handle == NULL) {
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printf("Error: %d\n", GetLastError());
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return 1;
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}
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#else
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*handle = dlopen(lib, flags);
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if (*handle == NULL) {
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printf("Error: %s\n", dlerror());
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return 1;
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}
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#endif
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return 0;
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}
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static inline int dyn_sym(dyn_handle_t handle, char *sym, void (**fp)(void)) {
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#if defined(WIN32) || defined(_WIN32)
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*fp = (void (*)(void))GetProcAddress(handle, sym);
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if (*fp == NULL) {
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printf("Error: %d\n", GetLastError());
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FreeLibrary(handle);
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return 1;
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}
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#else
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union {
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void *ptr;
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void (*fp)(void);
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} cast;
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cast.ptr = dlsym(handle, sym);
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if (cast.ptr == NULL) {
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printf("Error: %s\n", dlerror());
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dlclose(handle);
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return 1;
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}
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*fp = cast.fp;
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#endif
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return 0;
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}
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static inline void dyn_close(dyn_handle_t handle) {
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#if defined(WIN32) || defined(_WIN32)
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FreeLibrary(handle);
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#else
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dlclose(handle);
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#endif
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}
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static inline void dyn_symbol_info(void* symbol) {
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#if !defined(WIN32) && !defined(_WIN32) && !defined(__APPLE__)
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Dl_info info;
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if (dladdr(symbol, &info)) {
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printf("Symbol: %s\n", info.dli_sname);
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printf("Address: %p\n", info.dli_saddr);
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printf("Library: %s\n", (info.dli_fname ? info.dli_fname : "unknown"));
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} else {
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printf("Error: Failed to get symbol info.\n");
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}
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#endif
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}
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static inline void dyn_handle_info(dyn_handle_t handle) {
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#if !defined(WIN32) && !defined(_WIN32) && !defined(__APPLE__)
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const struct link_map *link_map = 0;
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const int ret = dlinfo(handle, RTLD_DI_LINKMAP, &link_map);
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assert(link_map != 0);
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printf("Libraries:\n");
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while (link_map->l_prev) {
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printf("%s\n", link_map->l_name);
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link_map = link_map->l_prev;
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}
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#endif
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}
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static inline dyn_handle_t dyn_current_process_handle(void) {
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#if defined(WIN32) || defined(_WIN32)
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return GetModuleHandle(NULL);
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#else
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return dlopen(NULL, RTLD_LAZY);
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#endif
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}
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#endif

‎source/libnode.c

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#include "libnode.h"
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char *string_function(void) {
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#ifdef NODE_STATIC
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return "node-static";
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#else
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return "node-dynamic";
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#endif
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}

‎source/libnode.h

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#ifndef LIBNODE
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#define LIBNODE 1
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#if defined(WIN32) || defined(_WIN32)
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#define EXPORT __declspec(dllexport)
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#else
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#define EXPORT __attribute__((visibility("default")))
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#endif
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EXPORT char *string_function(void);
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#endif

‎source/libnode2.c

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#include "libnode2.h"
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char *string_function(void) {
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return "libnode2";
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}
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char *string_function2(void) {
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return "libnode2";
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}

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