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  2. How can you use CaptureStackBackTrace to capture the exception stack, not the calling stack?

How can you use CaptureStackBackTrace to capture the exception stack, not the calling stack?

由 a 夏天 提交于 2019-11-27 19:31:33

On windows, unhandled C++ exception automatically generates SEH exception. SEH __except block allows to attach a filter that accepts _EXCEPTION_POINTERS structure as a parameter, which contains the pointer to the processor's context record in the moment exception was thrown. Passing this pointer to StackWalk64 function gives the stack trace in the moment of exception. So, this problem can be solved by using SEH-style exception handling instead of C++ style.

Example code:

#include <stdlib.h>
#include <locale.h>
#include <stdio.h>
#include <tchar.h>

#include <process.h>
#include <iostream>
#include <Windows.h>
#include "dbghelp.h"

using namespace std;

const int MaxNameLen = 256;

#pragma comment(lib,"Dbghelp.lib")

void printStack( CONTEXT* ctx ) //Prints stack trace based on context record
{
    BOOL    result;
    HANDLE  process;
    HANDLE  thread;
    HMODULE hModule;

    STACKFRAME64        stack;
    ULONG               frame;    
    DWORD64             displacement;

    DWORD disp;
    IMAGEHLP_LINE64 *line;

    char buffer[sizeof(SYMBOL_INFO) + MAX_SYM_NAME * sizeof(TCHAR)];
    char name[ MaxNameLen ];
    char module[MaxNameLen];
    PSYMBOL_INFO pSymbol = (PSYMBOL_INFO)buffer;

    memset( &stack, 0, sizeof( STACKFRAME64 ) );

    process                = GetCurrentProcess();
    thread                 = GetCurrentThread();
    displacement           = 0;
#if !defined(_M_AMD64)
    stack.AddrPC.Offset    = (*ctx).Eip;
    stack.AddrPC.Mode      = AddrModeFlat;
    stack.AddrStack.Offset = (*ctx).Esp;
    stack.AddrStack.Mode   = AddrModeFlat;
    stack.AddrFrame.Offset = (*ctx).Ebp;
    stack.AddrFrame.Mode   = AddrModeFlat;
#endif

    SymInitialize( process, NULL, TRUE ); //load symbols

    for( frame = 0; ; frame++ )
    {
        //get next call from stack
        result = StackWalk64
        (
#if defined(_M_AMD64)
            IMAGE_FILE_MACHINE_AMD64
#else
            IMAGE_FILE_MACHINE_I386
#endif
            ,
            process,
            thread,
            &stack,
            ctx,
            NULL,
            SymFunctionTableAccess64,
            SymGetModuleBase64,
            NULL
        );

        if( !result ) break;        

        //get symbol name for address
        pSymbol->SizeOfStruct = sizeof(SYMBOL_INFO);
        pSymbol->MaxNameLen = MAX_SYM_NAME;
        SymFromAddr(process, ( ULONG64 )stack.AddrPC.Offset, &displacement, pSymbol);

        line = (IMAGEHLP_LINE64 *)malloc(sizeof(IMAGEHLP_LINE64));
        line->SizeOfStruct = sizeof(IMAGEHLP_LINE64);       

        //try to get line
        if (SymGetLineFromAddr64(process, stack.AddrPC.Offset, &disp, line))
        {
            printf("\tat %s in %s: line: %lu: address: 0x%0X\n", pSymbol->Name, line->FileName, line->LineNumber, pSymbol->Address);
        }
        else
        { 
            //failed to get line
            printf("\tat %s, address 0x%0X.\n", pSymbol->Name, pSymbol->Address);
            hModule = NULL;
            lstrcpyA(module,"");        
            GetModuleHandleEx(GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS | GET_MODULE_HANDLE_EX_FLAG_UNCHANGED_REFCOUNT, 
                (LPCTSTR)(stack.AddrPC.Offset), &hModule);

            //at least print module name
            if(hModule != NULL)GetModuleFileNameA(hModule,module,MaxNameLen);       

            printf ("in %s\n",module);
        }       

        free(line);
        line = NULL;
    }
}

//******************************************************************************

void function2()
{
    int a = 0;
    int b = 0;
    throw new exception;
}

void function1()
{
    int a = 0;
    function2();
}

void function0()
{
    function1();
}

int seh_filter(_EXCEPTION_POINTERS* ex)
{
    printf("*** Exception 0x%x occured ***\n\n",ex->ExceptionRecord->ExceptionCode);    
    printStack(ex->ContextRecord);

    return EXCEPTION_EXECUTE_HANDLER;
}

static void threadFunction(void *param)
{    

    __try
    {
         function0();
    }
    __except(seh_filter(GetExceptionInformation()))
    {       
        printf("Exception \n");         
    }
}

int _tmain(int argc, _TCHAR* argv[])
{   
    _beginthread(threadFunction, 0, NULL);
    printf("Press any key to exit.\n");
    cin.get();
    return 0;
}

Example output (first two entries are noise, but the rest correctly reflects functions that caused exception):

*** Exception 0xe06d7363 occured ***

        at RaiseException, address 0xFD3F9E20.
in C:\Windows\system32\KERNELBASE.dll
        at CxxThrowException, address 0xDBB5A520.
in C:\Windows\system32\MSVCR110D.dll
        at function2 in c:\work\projects\test\test.cpp: line: 146: address: 0x3F9C6C00
        at function1 in c:\work\projects\test\test.cpp: line: 153: address: 0x3F9C6CB0
        at function0 in c:\work\projects\test\test.cpp: line: 158: address: 0x3F9C6CE0
        at threadFunction in c:\work\projects\test\test.cpp: line: 174: address: 0x3F9C6D70
        at beginthread, address 0xDBA66C60.
in C:\Windows\system32\MSVCR110D.dll
        at endthread, address 0xDBA66E90.
in C:\Windows\system32\MSVCR110D.dll
        at BaseThreadInitThunk, address 0x773C6520.
in C:\Windows\system32\kernel32.dll
        at RtlUserThreadStart, address 0x775FC520.
in C:\Windows\SYSTEM32\ntdll.dll

Another option is to create custom exception class that captures context in constructor and use it (or derived classes) to throw exceptions:

class MyException{
public:
    CONTEXT Context;

    MyException(){
        RtlCaptureContext(&Context);        
    }
};

void function2()
{    
    throw MyException();    
}

//...   

try
{
     function0();
}
catch(MyException e)
{       
    printf("Exception \n");     
    printStack(&e.Context);                 
}

If you wanted to capture the stack backtrace of the point where the code threw an exception, you must capture the stack backtrace in the ctor of the exception object and store it within the exception object. Hence the part calling CaptureStackBackTrace() should be moved to the constructor of the exception object, which should also provide methods to fetch it either as a vector of addresses or as a vector of symbols. This is exactly how Throwable in Java and Exception in C# operate.

Finally, please do not write:

throw new exception;

in C++, as you would in C# or Java. This is an excellent way to both produce memory leaks and to fail to catch the exceptions by type (as you are throwing pointers to these types). Rather use:

throw exception();

I'm aware that this is an old question but people (including myself) are still finding it.

标签
c++
winapi
visual-c++
stack
dbghelp
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