C++ EH Exception是Windows系统VC++里对c++语言的throw的分类和定义，它的代码就是0xe06d7363。在VC++里其本质也是SEH结构化异常机制。在我们分析用户崩溃的例子中经常会遇到它。一般情况下，遇到它，是我们代码里用throw抛出异常后没有处理导致程序崩溃。下面分析一下它的原理。
我们借助一段代码来跟踪和分析
class MyException
{
public:
int nErr;
char *szMessage;
public:
MyException(void)
:nErr(0)
, szMessage(NULL)
{
}
MyException(int nerr,char *szMess)
:nErr(nerr)
, szMessage(szMess)
{
}
~MyException(void)
{
}
};
int _tmain(int argc, _TCHAR* argv[])
{
try { MyException me(1, "test exception"); throw me; } catch (MyException me1) { printf("err=%s\n",me1.szMessage); }
}
将上述代码在VS2013里编译调试，转到汇编
91: try
92: {
01361797 mov dword ptr [ebp-4],0
93: MyException me(1, "test exception");
0136179E push 1367858h
013617A3 push 1
013617A5 lea ecx,[ebp-1Ch]
013617A8 call MyException::MyException (013610D2h)
013617AD mov dword ptr [ebp-104h],eax
013617B3 mov byte ptr [ebp-4],1
94: throw me;
013617B7 mov eax,dword ptr [ebp-1Ch]
013617BA mov dword ptr [ebp-0FCh],eax
013617C0 mov ecx,dword ptr [ebp-18h]
013617C3 mov dword ptr [ebp-0F8h],ecx
013617C9 push 1369084h
013617CE lea edx,[ebp-0FCh]
013617D4 push edx
013617D5 call __CxxThrowException@8 (0136111Dh)
95: }
我们可以看到，throw 首先通过下面的代码
013617B7 mov eax,dword ptr [ebp-1Ch] 013617BA mov dword ptr [ebp-0FCh],eax 013617C0 mov ecx,dword ptr [ebp-18h] 013617C3 mov dword ptr [ebp-0F8h],ecx
复制了一份异常对象MyException me，然后取了这份拷贝的地址作为参数传给了__CxxThrowException函数，同时将异常类型信息也传递了过去
013617CE lea edx,[ebp-0FCh] 013617D4 push edx
接着调用了__CxxThrowException函数，我们进入看看
下面是改函数的代码
/////////////////////////////////////////////////////////////////////////////
//
// _CxxThrowException - implementation of 'throw'
//
// Description:
// Builds the NT Exception record, and calls the NT runtime to initiate
// exception processing.
//
// Why is pThrowInfo defined as _ThrowInfo? Because _ThrowInfo is secretly
// snuck into the compiler, as is the prototype for _CxxThrowException, so
// we have to use the same type to keep the compiler happy.
//
// Another result of this is that _CRTIMP can't be used here. Instead, we
// synthesisze the -export directive below.
//
// Returns:
// NEVER. (until we implement resumable exceptions, that is)
//
// We want double underscore for CxxThrowException for ARM CE only
__declspec(noreturn) extern "C" void __stdcall
#if !defined(_M_ARM) || defined(_M_ARM_NT)
_CxxThrowException(
#else
__CxxThrowException(
#endif
void* pExceptionObject, // The object thrown
_ThrowInfo* pThrowInfo // Everything we need to know about it
) {
EHTRACE_ENTER_FMT1("Throwing object @ 0x%p", pExceptionObject);
static const EHExceptionRecord ExceptionTemplate = { // A generic exception record
EH_EXCEPTION_NUMBER, // Exception number
EXCEPTION_NONCONTINUABLE, // Exception flags (we don't do resume)
NULL, // Additional record (none)
NULL, // Address of exception (OS fills in)
EH_EXCEPTION_PARAMETERS, // Number of parameters
{ EH_MAGIC_NUMBER1, // Our version control magic number
NULL, // pExceptionObject
NULL,
#if _EH_RELATIVE_OFFSETS
NULL // Image base of thrown object
#endif
} // pThrowInfo
};
EHExceptionRecord ThisException = ExceptionTemplate; // This exception
ThrowInfo* pTI = (ThrowInfo*)pThrowInfo;
if (pTI && (THROW_ISWINRT( (*pTI) ) ) )
{
ULONG_PTR *exceptionInfoPointer = *reinterpret_cast<ULONG_PTR**>(pExceptionObject);
exceptionInfoPointer--; // The pointer to the ExceptionInfo structure is stored sizeof(void*) infront of each WinRT Exception Info.
WINRTEXCEPTIONINFO** ppWei = reinterpret_cast<WINRTEXCEPTIONINFO**>(exceptionInfoPointer);
pTI = (*ppWei)->throwInfo;
(*ppWei)->PrepareThrow( ppWei );
}
//
// Fill in the blanks:
//
ThisException.params.pExceptionObject = pExceptionObject;
ThisException.params.pThrowInfo = pTI;
#if _EH_RELATIVE_OFFSETS
PVOID ThrowImageBase = RtlPcToFileHeader((PVOID)pTI, &ThrowImageBase);
ThisException.params.pThrowImageBase = ThrowImageBase;
#endif
//
// If the throw info indicates this throw is from a pure region,
// set the magic number to the Pure one, so only a pure-region
// catch will see it.
//
// Also use the Pure magic number on Win64 if we were unable to
// determine an image base, since that was the old way to determine
// a pure throw, before the TI_IsPure bit was added to the FuncInfo
// attributes field.
//
if (pTI != NULL)
{
if (THROW_ISPURE(*pTI))
{
ThisException.params.magicNumber = EH_PURE_MAGIC_NUMBER1;
}
#if _EH_RELATIVE_OFFSETS
else if (ThrowImageBase == NULL)
{
ThisException.params.magicNumber = EH_PURE_MAGIC_NUMBER1;
}
#endif
}
//
// Hand it off to the OS:
//
EHTRACE_EXIT;
#if defined(_M_X64) && defined(_NTSUBSET_)
RtlRaiseException( (PEXCEPTION_RECORD) &ThisException );
#else
RaiseException( ThisException.ExceptionCode,
ThisException.ExceptionFlags,
ThisException.NumberParameters,
(PULONG_PTR)&ThisException.params );
#endif
}
可以看到，这个函数首先是创建了一个EHExceptionRecord 对象，其实对应的就是 SEH里的结构EXCEPTION_RECORD，并且给这个结构成员赋值。
在这里通过如下代码，0xe06d7363就赋值给ThisException.ExceptionCode
还有就是将ThrowInfo赋值给EHExceptionRecordThisException.params.pThrowInfo。_ThrowInfo 结构体定义如下：
typedef const struct _s__ThrowInfo
{
unsigned int attributes;
_PMFN pmfnUnwind;
int (__cdecl*pForwardCompat)(...);
_CatchableTypeArray *pCatachableTypeArray;
} _ThrowInfo;
结构体中重要的成员是_CatchableTypeArray。它包含了程序运行时抛出对象的类新信息(RTTI).
如果你的程序运行时抛出一个my_exception类型的对象，那么抛出的数据参数pCatchableTypeArray包含了两个重要子数据信息。一个是typeid(my_exception)，另外一个是typeid(std::exception)。
在我们的例子里
紧接着就调用RaiseException函数进入了异常的分发过程。
综上，在C++ EH Exception 的异常里，EXCEPTION_RECORD结构填充如下：
ExceptionAddress: 异常地址 ExceptionCode: 异常代码 e06d7363 (C++ EH exception) ExceptionFlags: 标志 00000001 NumberParameters: 3 or 4 64位时是4 Parameter[0]: 0000000019930520 //魔数 Parameter[1]: 00000000015def30 // 抛出的异常对象指针 Parameter[2]: 00000000100cefa8 // 异常对象类型信息 Parameter[3]: 0000000010000000 // 64位下模块句柄HINSTANCE