如何找到C++中抛出异常的位置？

Question

我有一个程序在某处抛出未捕获的异常.我得到的只是一个抛出异常的报告,并没有关于它被抛出的信息.编译为包含调试符号的程序似乎不合逻辑,不通知我在代码中生成异常的位置.

有没有办法告诉我的地方是例外,从短期在gdb设置"抓扔",并呼吁每一个抛出的异常回溯的到来？

Answer 1

这里有一些可能用于调试问题的信息

如果未捕获异常,std::terminate()则会自动调用特殊库函数.Terminate实际上是一个指向函数的指针,默认值是标准C库函数std::abort().如果没有清理发生了未捕获的异常^†,它可能实际上是因为没有析构函数调用调试这个问题有帮助.
_{†无论堆栈是否在std::terminate()被调用之前被展开,它都是实现定义的.}

调用abort()通常可用于生成可以分析以确定异常原因的核心转储.确保通过ulimit -c unlimited(Linux)启用核心转储.

您可以使用安装自己的terminate()功能std::set_terminate().您应该能够在gdb中的终止函数上设置断点.您可以从terminate()函数生成堆栈回溯,此回溯可能有助于识别异常的位置.

在Bruce Eckel的C++思考中,对于未被捕获的异常进行了简短的讨论,第二版也可能有所帮助.

由于默认情况下terminate()调用abort()(默认情况下将导致SIGABRT信号),您可以设置SIGABRT处理程序,然后从信号处理程序中打印堆栈回溯.此回溯可能有助于识别异常的位置.

注意:我说可能是因为C++通过使用语言结构来支持非本地错误处理,以将错误处理和报告代码与普通代码分开.捕获块可以并且通常位于与投掷点不同的功能/方法中.在评论中也向我指出(感谢Dan),无论堆栈是否在terminate()被调用之前被解开,它都是实现定义的.

更新:我扔在一起称为Linux的测试程序,在生成回溯terminate()通过设置功能set_terminate()在信号处理和另一种SIGABRT.两个回溯都正确显示未处理异常的位置.

更新2:感谢一篇关于在终止中捕获未捕获异常的博客文章,我学到了一些新的技巧; 包括在终止处理程序中重新抛出未捕获的异常.请务必注意,throw自定义终止处理程序中的空语句适用于GCC,而不是可移植的解决方案.

码:

#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif
#ifndef __USE_GNU
#define __USE_GNU
#endif

#include <execinfo.h>
#include <signal.h>
#include <string.h>

#include <iostream>
#include <cstdlib>
#include <stdexcept>

void my_terminate(void);

namespace {
    // invoke set_terminate as part of global constant initialization
    static const bool SET_TERMINATE = std::set_terminate(my_terminate);
}

// This structure mirrors the one found in /usr/include/asm/ucontext.h
typedef struct _sig_ucontext {
   unsigned long     uc_flags;
   struct ucontext   *uc_link;
   stack_t           uc_stack;
   struct sigcontext uc_mcontext;
   sigset_t          uc_sigmask;
} sig_ucontext_t;

void crit_err_hdlr(int sig_num, siginfo_t * info, void * ucontext) {
    sig_ucontext_t * uc = (sig_ucontext_t *)ucontext;

    // Get the address at the time the signal was raised from the EIP (x86)
    void * caller_address = (void *) uc->uc_mcontext.eip;

    std::cerr << "signal " << sig_num 
              << " (" << strsignal(sig_num) << "), address is " 
              << info->si_addr << " from " 
              << caller_address << std::endl;

    void * array[50];
    int size = backtrace(array, 50);

    std::cerr << __FUNCTION__ << " backtrace returned " 
              << size << " frames\n\n";

    // overwrite sigaction with caller's address
    array[1] = caller_address;

    char ** messages = backtrace_symbols(array, size);

    // skip first stack frame (points here)
    for (int i = 1; i < size && messages != NULL; ++i) {
        std::cerr << "[bt]: (" << i << ") " << messages[i] << std::endl;
    }
    std::cerr << std::endl;

    free(messages);

    exit(EXIT_FAILURE);
}

void my_terminate() {
    static bool tried_throw = false;

    try {
        // try once to re-throw currently active exception
        if (!tried_throw++) throw;
    }
    catch (const std::exception &e) {
        std::cerr << __FUNCTION__ << " caught unhandled exception. what(): "
                  << e.what() << std::endl;
    }
    catch (...) {
        std::cerr << __FUNCTION__ << " caught unknown/unhandled exception." 
                  << std::endl;
    }

    void * array[50];
    int size = backtrace(array, 50);    

    std::cerr << __FUNCTION__ << " backtrace returned " 
              << size << " frames\n\n";

    char ** messages = backtrace_symbols(array, size);

    for (int i = 0; i < size && messages != NULL; ++i) {
        std::cerr << "[bt]: (" << i << ") " << messages[i] << std::endl;
    }
    std::cerr << std::endl;

    free(messages);

    abort();
}

int throw_exception() {
    // throw an unhandled runtime error
    throw std::runtime_error("RUNTIME ERROR!");
    return 0;
}

int foo2() {
    throw_exception();
    return 0;
}

int foo1() {
    foo2();
    return 0;
}

int main(int argc, char ** argv) {
    struct sigaction sigact;

    sigact.sa_sigaction = crit_err_hdlr;
    sigact.sa_flags = SA_RESTART | SA_SIGINFO;

    if (sigaction(SIGABRT, &sigact, (struct sigaction *)NULL) != 0) {
        std::cerr << "error setting handler for signal " << SIGABRT 
                  << " (" << strsignal(SIGABRT) << ")\n";
        exit(EXIT_FAILURE);
    }

    foo1();

    exit(EXIT_SUCCESS);
}

输出:

my_terminate caught unhanded exception. what(): RUNTIME ERROR!
my_terminate backtrace returned 10 frames

[bt]: (0) ./test(my_terminate__Fv+0x1a) [0x8048e52]
[bt]: (1) /usr/lib/libstdc++-libc6.2-2.so.3 [0x40045baa]
[bt]: (2) /usr/lib/libstdc++-libc6.2-2.so.3 [0x400468e5]
[bt]: (3) /usr/lib/libstdc++-libc6.2-2.so.3(__rethrow+0xaf) [0x40046bdf]
[bt]: (4) ./test(throw_exception__Fv+0x68) [0x8049008]
[bt]: (5) ./test(foo2__Fv+0xb) [0x8049043]
[bt]: (6) ./test(foo1__Fv+0xb) [0x8049057]
[bt]: (7) ./test(main+0xc1) [0x8049121]
[bt]: (8) ./test(__libc_start_main+0x95) [0x42017589]
[bt]: (9) ./test(__eh_alloc+0x3d) [0x8048b21]

signal 6 (Aborted), address is 0x1239 from 0x42029331
crit_err_hdlr backtrace returned 13 frames

[bt]: (1) ./test(kill+0x11) [0x42029331]
[bt]: (2) ./test(abort+0x16e) [0x4202a8c2]
[bt]: (3) ./test [0x8048f9f]
[bt]: (4) /usr/lib/libstdc++-libc6.2-2.so.3 [0x40045baa]
[bt]: (5) /usr/lib/libstdc++-libc6.2-2.so.3 [0x400468e5]
[bt]: (6) /usr/lib/libstdc++-libc6.2-2.so.3(__rethrow+0xaf) [0x40046bdf]
[bt]: (7) ./test(throw_exception__Fv+0x68) [0x8049008]
[bt]: (8) ./test(foo2__Fv+0xb) [0x8049043]
[bt]: (9) ./test(foo1__Fv+0xb) [0x8049057]
[bt]: (10) ./test(main+0xc1) [0x8049121]
[bt]: (11) ./test(__libc_start_main+0x95) [0x42017589]
[bt]: (12) ./test(__eh_alloc+0x3d) [0x8048b21]

Answer 2

正如你所说,我们可以在gdb中使用'catch throw'并为每个抛出的异常调用'backtrace'.虽然手动操作通常太繁琐,但gdb允许自动化过程.这允许查看抛出的所有异常的回溯,包括最后一个未被捕获的异常:

GDB>

set pagination off
catch throw
commands
backtrace
continue
end
run

如果没有进一步的人工干预,这会产生大量的回溯,包括最后一次未捕获的异常:

Catchpoint 1 (exception thrown), 0x00a30 in __cxa_throw () from libstdc++.so.6
#0  0x0da30 in __cxa_throw () from /usr/.../libstdc++.so.6
#1  0x021f2 in std::__throw_bad_weak_ptr () at .../shared_ptr_base.h:76
[...]
terminate called after throwing an instance of 'std::bad_weak_ptr'
  what():  bad_weak_ptr
Program received signal SIGABRT, Aborted.

这是一篇很好的博客文章:http://741mhz.com/throw-stacktrace/

Answer 3

您可以创建一个宏,如:

#define THROW(exceptionClass, message) throw exceptionClass(__FILE__, __LINE__, (message) )

...它将为您提供抛出异常的位置(当然不是堆栈跟踪).您需要从一些采用上述构造函数的基类派生您的异常.

Answer 4

您没有传递有关您使用的OS /编译器的信息.

在Visual Studio C++中,可以检测异常.

请参阅 ddj.com上的"Visual C++异常处理检测"

我的文章" Postmortem Debugging",也在ddj.com上,包括使用Win32结构化异常处理(由仪器使用)进行日志记录等的代码.

Answer 5

您可以将代码中的主要位置标记为noexcept定位异常，然后使用libunwind（只需添加-lunwind到链接器参数）（已通过测试clang++ 3.6）：

demagle.hpp：

#pragma once

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

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);
}

backtrace.hpp：

#pragma once
#include <ostream>

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

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;
}

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 std::exception:what(): " << 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); // change to desired return code
}

}

有关于这个问题的好文章。