c++ - 使用 SEH 时如何解释 GetExceptionCode 结果？

Question

我一直在尝试编写一些错误保护条款来识别第三方提供给我们的 dll 中的问题。此 dll 中可能存在问题(内存异常、浮点错误等)，能够在不访问源代码的情况下识别这些错误是有利的。

我从各种 SEH 错误处理例程中收集了一些东西，但尽管它有效，但有几个...与它不一致。我试图将每个人都隔离开来，我将针对每个人单独提出一个问题。

这是与 GetExceptionCode 相关的，在 SEH __try/__except 子句中用于识别错误。它似乎并不可靠。

这是一个明显的被零除的情况:

#include <float.h>      // defines of _EM_OVERFLOW, etc.
#include <string.h>     // strncpy_s & strncat_s
#include <stdlib.h>     // malloc
#include <excpt.h>      // EXCEPTION_EXECUTE_HANDLER
#include <iostream>     // cout
#include <bitset>       // bitset
#include <conio.h>      // _kbhit
#pragma fenv_access (on)


const unsigned int SERIOUS_FP_EXCEPTIONS = _EM_DENORMAL | _EM_ZERODIVIDE | _EM_INVALID;
const unsigned int MINOR_FP_EXCEPTIONS = _EM_OVERFLOW | _EM_UNDERFLOW | _EM_INEXACT;

int main(int argc, char[])
{
    double numerator = 1.0;
    double denominator = 0.0;
    double result = 0.0;

    unsigned int _previous_floating_point_control;
    _controlfp_s(&_previous_floating_point_control, 0, 0);
    _controlfp_s(nullptr, MINOR_FP_EXCEPTIONS, _MCW_EM);
    __try {
        result = numerator / denominator;
        _controlfp_s(NULL, _previous_floating_point_control, _MCW_EM);
    }
    __except (EXCEPTION_EXECUTE_HANDLER)
    {
        std::cout << "_EM_INEXACT    = " << std::bitset<32>(_EM_INEXACT) << std::endl;
        std::cout << "_EM_UNDERFLOW  = " << std::bitset<32>(_EM_UNDERFLOW) << std::endl;
        std::cout << "_EM_OVERFLOW   = " << std::bitset<32>(_EM_OVERFLOW) << std::endl;
        std::cout << "_EM_ZERODIVIDE = " << std::bitset<32>(_EM_ZERODIVIDE) << std::endl;
        std::cout << "_EM_INVALID    = " << std::bitset<32>(_EM_INVALID) << std::endl;
        std::cout << "_EM_DENORMAL   = " << std::bitset<32>(_EM_DENORMAL) << std::endl;
        std::cout << "_EM_AMBIGUOUS  = " << std::bitset<32>(_EM_AMBIGUOUS) << std::endl;
        std::cout << std::endl;
        std::cout << "                                      divide-by-zero" << std::endl;
        std::cout << "                                             |" << std::endl;
        std::cout << "            ambiguous code?                underflow" << std::endl;
        std::cout << "                  |                          : |" << std::endl;
        std::cout << "                  v                          v v" << std::endl;
        std::cout << "Exception code = " << std::bitset<32>(GetExceptionCode()) << std::endl;
        std::cout << "                             ^              ^ ^ ^" << std::endl;
        std::cout << "                             |              : : |" << std::endl;
        std::cout << "                     denormal number     inexact number" << std::endl;
        std::cout << "                                            : |" << std::endl;
        std::cout << "                                          overflow" << std::endl;
        std::cout << "                                            |" << std::endl;
        std::cout << "                                     invalid number" << std::endl;

        if (GetExceptionCode() & _EM_ZERODIVIDE)
            std::cout << "ERROR! Divide By Zero!" << std::endl;
        else
            std::cout << "No divide by zero found here!" << std::endl;
        _controlfp_s(NULL, _previous_floating_point_control, _MCW_EM);
    }

    std::cout << "result = " << result << std::endl;

    while (!_kbhit())   // Wait until a key is pressed to close console.
    { }
}

这会打印以下内容:

_EM_INEXACT    = 00000000000000000000000000000001
_EM_UNDERFLOW  = 00000000000000000000000000000010
_EM_OVERFLOW   = 00000000000000000000000000000100
_EM_ZERODIVIDE = 00000000000000000000000000001000
_EM_INVALID    = 00000000000000000000000000010000
_EM_DENORMAL   = 00000000000010000000000000000000
_EM_AMBIGUOUS  = 10000000000000000000000000000000

                                      divide-by-zero
                                             |
            ambiguous code?                underflow
                  |                          : |
                  v                          v v
Exception code = 11000000000000000000001010110101
                             ^              ^ ^ ^
                             |              : : |
                     denormal number     inexact number
                                            : |
                                          overflow
                                            |
                                     invalid number
No divide by zero found here!
result = 0

它发现了一个问题(很好)，但还没有完全正确地诊断它。

更糟糕的是，当该子句被替换为对缺少依赖项的 dll 的调用时，我得到:

                       f.p. exceptions
     denormal number         |
            |               _|_
            v              /   \
11000000011011010000000001111110
         ^^  ^ ^         ^^
         ||  | |         ||
         \________________/
           unknown codes

在 SIGSEV 错误(段错误)的情况下会返回类似的结果。这意味着我们将其他问题误诊为浮点异常。

所以我的问题是:

1. 这种一般方法是否正确，还是我误解了什么基础？
2. 为什么这不采用被零除的简单情况？是否依赖于硬件？
3. 我能否找出来自 GetExceptionCode() 的其余错误位是什么 - 这将真的有用。

PS:请不要评论或回复说我应该检查分母是否为 0 - 我知道，我在我控制的所有代码中都这样做。

Answer 1

你需要一些类似的东西

DWORD exception_filter(DWORD dwExceptionCode)
{
    // use dwExceptionCode to handle only the types of exceptions you want
    // if you want to use it inside your handler, you'll need to save it.
    return EXCEPTION_EXECUTE_HANDLER; // or other value depending on ExceptionCode
}

Your exception handler...

__try
{
    something();
}
__except (exception_filter(GetExceptionCode())
{
    // DO NOT CALL GetExceptionCode() or GetExceptionInfo() here. If you need
    // Exception Info as well, pass it to the filter, and save the values you need.
    switch (dwSavedExceptionCode)
    {
        case EXCEPTION_FLT_OVERFLOW:
              ItWasAFloatingPointOverflow(); 
              break;
        case EXCEPTION_FLT_DIVIDE_BY_ZERO:
              ItWasAFloatingDivideByZero(); 
              break;
        case ***Other Exception Types You Want handled (==the ones you returned execute_handler for in the filter) ***
              break;
    }
}