CODEWITHSUNDEEP
c++xcodemacos
Tilo
Tilo

Reputation: 3325

EXC_BAD_ACCESS on throwing exception

I'm having a problem with a shared library provided by one of our partners and narrowed it down to this test case:

My own test library compiled to libCrashTestLib.dylib:

#include <exception>
#include <iostream>

extern "C" void Test() {
  try {
    throw std::exception{};
  } catch (const std::exception& e) { }
  std::cout << "Success" << std::endl;
}

My main executable loads my library and calls the Test function:

#include <string>
#include <dlfcn.h>

int main(int argc, char** argv) {
  std::string lib_path = "/path/to/libCrashTestLib.dylib";

  void* handle = dlopen(lib_path.c_str(), RTLD_NOW | RTLD_GLOBAL);
  void (*test_pointer)() = reinterpret_cast<void(*)()>(dlsym(handle, "Test"));
  test_pointer();
  dlclose(handle);
}

This works fine and prints Success.

However, when I just link (not even call) the library provided by our partner it gives me an EXC_BAD_ACCESS where I throw the exception.

What I'm looking for is either of two things:

For completeness, here is the CMakeLists.txt I'm using:

cmake_minimum_required(VERSION 3.0)
project(CrashTest CXX)

set(CMAKE_CXX_STANDARD 14)
set(CMAKE_CXX_STANDARD_REQUIRED on)

find_library(VendorApi NAMES vendorapi PATHS ${CMAKE_SOURCE_DIR}) 

add_library(CrashTestLib SHARED lib.cpp)
# Uncomment this line to make it crash:
#target_link_libraries(CrashTestLib VendorApi)

add_executable(CrashTestMain main.cpp)

Upvotes: 1

Views: 721

Answers (1)

Anya Shenanigans
Anya Shenanigans

Reputation: 94654

The most likely reason for the crash is that the vendor's library is compiled with libstdc++, while your code is compliled with libc++.

I can trigger a crash quite easily by issuing a cout while constructing a class as part of the library load-time e.g.

#include <exception>
#include <iostream>
#include <string>

class bongo {

    public:
    bongo() {
        std::cout << "Log something" << std::endl;
    }
};

static class bongo *boing;

void __attribute__((constructor)) start_something(void) {
    boing = new bongo;
}


extern "C" void Test() {
  try {
    throw std::exception{};
  } catch (const std::exception& e) { }
  std::cout << "Success" << std::endl;
}

loader code:

#include <string>
#include <dlfcn.h>

int main(int argc, char** argv) {
  std::string lib_path = "./libCrashTestLib.dylib";

  void* handle = dlopen(lib_path.c_str(), RTLD_NOW | RTLD_GLOBAL);
  void (*test_pointer)() = reinterpret_cast<void(*)()>(dlsym(handle, "Test"));
  test_pointer();
  dlclose(handle);
}

Makefile:

CXXFLAGS += -std=c++11
STDLIB = -stdlib=libstdc++

all: libCrashTestLib.dylib testLib

libCrashTestLib.dylib: CrashTest.cpp
    $(CXX) $(CXXFLAGS) $(STDLIB) -shared -o $@ $<

testLib: testLib.cpp
    $(CXX) $(CXXFLAGS) -o $@ $<

clean:
    rm -f *.dylib testLib

Invocation:

$ make clean && make STDLIB= && ./testLib
rm -f *.dylib testLib
c++ -std=c++11  -shared -o libCrashTestLib.dylib CrashTest.cpp
c++ -std=c++11 -o testLib testLib.cpp
Log something
Success

Failing invocation:

$ make clean && make && ./testLib
rm -f *.dylib testLib
c++ -std=c++11 -stdlib=libstdc++ -shared -o libCrashTestLib.dylib CrashTest.cpp
c++ -std=c++11 -o testLib testLib.cpp
Segmentation fault: 11

You can check what version of the C++ library is linked to the binary using otool -L:

$ otool -L libCrashTestLib.dylib
libCrashTestLib.dylib:
    libCrashTestLib.dylib (compatibility version 0.0.0, current version 0.0.0)
    /usr/lib/libstdc++.6.dylib (compatibility version 7.0.0, current version 104.1.0)
    /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1226.10.1)

Upvotes: 2

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