02 March, 2014

Decoding the parameters of a thrown C++ exception (0xE06D7363)

I have a lot questions after reading the post about decoding structural exception 0xE06D7363 from "The Old New Thing". I like computer magic like that: take address from here add the constant two and half time and you get it. However, this magic don't help to understand how it really works and what happened if I do that. So, following code from CRT kill all magic.

Welcome - ehdata.h. This header appears only in VS2012 and VS2013 (see "%Program Files (x86)%\Microsoft Visual Studio 12.0\VC\crt\src\ehdata.h"):

typedef struct EHExceptionRecord {
 DWORD  ExceptionCode;   // The code of this exception. (= EH_EXCEPTION_NUMBER)
 DWORD  ExceptionFlags;   // Flags determined by NT
    struct _EXCEPTION_RECORD *ExceptionRecord; // An extra exception record (not used)
    void *   ExceptionAddress;  // Address at which exception occurred
    DWORD   NumberParameters;  // Number of extended parameters. (= EH_EXCEPTION_PARAMETERS)
 struct EHParameters {
  DWORD  magicNumber;  // = EH_MAGIC_NUMBER1
  void *  pExceptionObject; // Pointer to the actual object thrown
  ThrowInfo *pThrowInfo;  // Description of thrown object
  void  *pThrowImageBase; // Image base of thrown object
  } params;
} EHExceptionRecord;


typedef const struct _s_ThrowInfo {
 unsigned int attributes;   // Throw Info attributes (Bit field)
 PMFN   pmfnUnwind;   // Destructor to call when exception
          // has been handled or aborted.
#if _EH_RELATIVE_OFFSETS && !defined(VERSP_IA64) && !defined(_M_CEE_PURE) /*IFSTRIP=IGN*/
 __int32   pForwardCompat;  // Image relative offset of Forward compatibility frame handler
 __int32   pCatchableTypeArray;// Image relative offset of CatchableTypeArray
#if defined(__cplusplus)
 int (__cdecl* _EH_PTR64 pForwardCompat)(...); // Forward compatibility frame handler
 int (__cdecl* _EH_PTR64 pForwardCompat)(); // Forward compatibility frame handler
 CatchableTypeArray * _EH_PTR64 pCatchableTypeArray; // Pointer to list of pointers to types.
} ThrowInfo;


typedef const struct _s_CatchableTypeArray {
 int nCatchableTypes;
#if _EH_RELATIVE_OFFSETS && !defined(VERSP_IA64) && !defined(_M_CEE_PURE) /*IFSTRIP=IGN*/
 __int32   arrayOfCatchableTypes[]; // Image relative offset of Catchable Types
 CatchableType * _EH_PTR64 arrayOfCatchableTypes[];
 } CatchableTypeArray;


typedef const struct _s_CatchableType {
 unsigned int properties;    // Catchable Type properties (Bit field)
#if _EH_RELATIVE_OFFSETS && !defined(VERSP_IA64) && !defined(_M_CEE_PURE) /*IFSTRIP=IGN*/
 __int32   pType;     // Image relative offset of TypeDescriptor
 TypeDescriptor * _EH_PTR64 pType;  // Pointer to the type descriptor for this type
 PMD    thisDisplacement;  // Pointer to instance of catch type within
           //  thrown object.
 int    sizeOrOffset;   // Size of simple-type object or offset into
           //  buffer of 'this' pointer for catch object
 PMFN   copyFunction;   // Copy constructor or CC-closure
} CatchableType;


typedef struct TypeDescriptor
#if defined(_WIN64) || defined(_RTTI) /*IFSTRIP=IGN*/
 const void * _EH_PTR64 pVFTable; // Field overloaded by RTTI
 DWORD hash;   // Hash value computed from type's decorated name
 void * _EH_PTR64   spare;  // reserved, possible for RTTI
 char name[];   // The decorated name of the type; 0 terminated.
 } TypeDescriptor;
P.S. _EH_RELATIVE_OFFSETS is defined as 1 only in 64-bit mode

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