cpp-exception-interposer

This library intercepts any thrown C++ exception, and prints a stack trace of the point it was thrown from - even if the exception is caught and ignored.

It's useful for debugging exceptions in cases where using gdb and catch throw is difficult, or for profiling applications that may be inefficiently using C++ exceptions for mainline control flow.

It's licensed under the 3-clause BSD license (https://github.com/rkday/cpp-exception-interposer/releases), as is libbacktrace (https://github.com/ianlancetaylor/libbacktrace/blob/ca0de0517f3be44fedf5a2c01cfaf6437d4cae68/LICENSE), which is statically linked into the .so.

Downloading

The .so is available from https://github.com/rkday/cpp-exception-interposer/releases.

Compiling

To compile from source:

• check out this repository (and the libbacktrace submodule) with git clone --recursive
• run ./build.sh

Running

You can use this by setting LD_PRELOAD=cpp_exception_interposer.so.

For example, this program (compiled with g++ -g -std=c++17 -o exceptions exceptions.cpp):

#include <stdexcept>
#include <stdio.h>
#include <optional>

void foo()
{
  std::optional<int> x;
  x.value();
}

void bar()
{
  try {
    foo();
  } catch (std::exception& e) {
    printf("Exception caught and ignored\n");
  }
}

int main()
{
  bar();
}

normally provides this output:

$ ./exceptions 
Exception caught and ignored

but running it with the interposer provides much better diagnostics:

$ LD_PRELOAD=cpp-exception-interposer/cpp_exception_interposer.so ./exceptions 
*** C++ exception (St19bad_optional_access) thrown ***
0x7fa4646ee451 ???
  ???:0
0x55958f3f12ea _ZSt27__throw_bad_optional_accessv
  /usr/include/c++/9.3.0/optional:99
0x55958f3f132c _ZNRSt8optionalIiE5valueEv
  /usr/include/c++/9.3.0/optional:931
0x55958f3f11e3 _Z3foov
  /home/rkd/src/exceptions.cpp:8
0x55958f3f1208 _Z3barv
  /home/rkd/src/exceptions.cpp:14
0x55958f3f125a main
  /home/rkd/src/exceptions.cpp:22
0x7fa4641ca022 ???
  ???:0
0x55958f3f10ed ???
  ???:0
0xffffffffffffffff ???
  ???:0
*** Proceeding with C++ exception handling ***
Exception caught and ignored