backtrace on terminate

// interface: demagle.hpp
#pragma once

char const *
get_demangled_name(char const * const symbol) noexcept;

//interface: backtrace.hpp
#pragma once
#include <ostream>

void
backtrace(std::ostream & _out) noexcept;

// implementation: demangle.cpp
#include "demangle.hpp"

#include <memory>

#include <cstdlib>

#include <cxxabi.h>

namespace
{

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wglobal-constructors"
#pragma clang diagnostic ignored "-Wexit-time-destructors"
std::unique_ptr< char, decltype(std::free) & > demangled_name{nullptr, std::free};
#pragma clang diagnostic pop

}

char const *
get_demangled_name(char const * const symbol) noexcept
{
    if (!symbol) {
        return "<null>";
    }
    int status = -4;
    demangled_name.reset(abi::__cxa_demangle(symbol, demangled_name.release(), nullptr, &status));
    return ((status == 0) ? demangled_name.get() : symbol);
}

// implementation: backtrace.cpp
#include "backtrace.hpp"

#include <iostream>
#include <iomanip>
#include <limits>
#include <ostream>

#include <cstdint>

#define UNW_LOCAL_ONLY
#include <libunwind.h>

namespace
{

void
print_reg(std::ostream & _out, unw_word_t reg) noexcept
{
    constexpr std::size_t address_width = std::numeric_limits< std::uintptr_t >::digits / 4;
    _out << "0x" << std::setfill('0') << std::setw(address_width) << reg;
}

char symbol[1024];

}

void
backtrace(std::ostream & _out) noexcept
{
    unw_cursor_t cursor;
    unw_context_t context;
    unw_getcontext(&context);
    unw_init_local(&cursor, &context);
    _out << std::hex << std::uppercase;
    while (0 < unw_step(&cursor)) {
        unw_word_t ip = 0;
        unw_get_reg(&cursor, UNW_REG_IP, &ip);
        if (ip == 0) {
            break;
        }
        unw_word_t sp = 0;
        unw_get_reg(&cursor, UNW_REG_SP, &sp);
        print_reg(_out, ip);
        _out << ": (SP:";
        print_reg(_out, sp);
        _out << ") ";
        unw_word_t offset = 0;
        if (unw_get_proc_name(&cursor, symbol, sizeof(symbol), &offset) == 0) {
            _out << "(" << get_demangled_name(symbol) << " + 0x" << offset << ")\n\n";
        } else {
            _out << "-- error: unable to obtain symbol name for this frame\n\n";
        }
    }
    _out << std::flush;
}

// implementation: backtrace_on_terminate.hpp
#include "demangle.hpp"
#include "backtrace.hpp"

#include <iostream>
#include <type_traits>
#include <exception>
#include <memory>
#include <typeinfo>

#include <cstdlib>

#include <cxxabi.h>

namespace
{

[[noreturn]]
void
backtrace_on_terminate() noexcept;

static_assert(std::is_same< std::terminate_handler, decltype(&backtrace_on_terminate) >{});

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wglobal-constructors"
#pragma clang diagnostic ignored "-Wexit-time-destructors"
std::unique_ptr< std::remove_pointer_t< std::terminate_handler >, decltype(std::set_terminate) & > terminate_handler{std::set_terminate(backtrace_on_terminate), std::set_terminate};
#pragma clang diagnostic pop

[[noreturn]]
void
backtrace_on_terminate() noexcept
{
    std::set_terminate(terminate_handler.release()); // to avoid infinite looping if any
    backtrace(std::clog);
    if (std::exception_ptr ep = std::current_exception()) {
        try {
            std::rethrow_exception(ep);
        } catch (std::exception const & e) {
            std::clog << "backtrace: unhandled exception derived from std::exception: " << e.what() << std::endl;
        } catch (...) {
            if (std::type_info * et = abi::__cxa_current_exception_type()) {
                std::clog << "backtrace: unhandled exception type: " << get_demangled_name(et->name()) << std::endl;
            } else {
                std::clog << "backtrace: unhandled unknown exception" << std::endl;
            }
        }
    }
    std::_Exit(EXIT_FAILURE);
}

}