Add Crash Reporting to Your Applications

Figure 1—Main Dialog

Environment: VC6, Win2K/XP

Contents

Overview
Usage
Using the CrashRpt Library in Your Application
Using the Crash Report
Deployment
References and Related Links
Change History

Overview

If you've ever been tasked with debugging a fatal exception, you probably know how difficult it can be given only the user's steps to reproduce. Many factors, such as the application's version, user's operating system, and dependent modules may contribute to the eventual crash. This makes duplicating the user's environment, and thereby the crash, nearly impossible for all but the most obvious bugs.

The CrashRpt library is a lite-weight, error-handling framework. This module will intercept any unhandled exception generated by your application, build a complete debug report, and, optionally, mail the report to you.

Usage

In this article, a crash report refers to a collection of files intended to help the developer quickly diagnose the cause of a crash. Specifically, the crash report includes a minidump, a crash log, and up to ten additional application specific files supplied by the application via a crash callback. Of these, the most useful will most likely be the application minidump. The minidump contains the call stack, local variables, details all of your application's modules, and can even help pinpoint the source line number that generated the exception.

The CrashRpt DLL works like the new Dr. Watson utility that ships with XP. It intercepts unhandled exceptions, creates a minidump, builds a crash log, presents an interface to allow the user to review the crash report, and finally, it compresses and optionally e-mails the crash report back to you.

When an unhandled exception is detected, CrashRpt notifies the user and allows him to review the report contents. First, the main dialog shown above is displayed. From here, the user can enter his comments and e-mail address or review the report contents by clicking the hyperlink. This takes him to the details dialog where he is presented with the files that make up the report. Double-clicking on the filename will open that file in its associated program, if an association exists for that file type.

Figure 2—Crash Details Dialog

Once the user is satisfied, he may close the details dialog and click the 'Send' button on the main dialog, which will e-mail the complete crash report to you.

Using the CrashRpt library in Your Application

Building the library

Download and unzip the source code attached to this article. Open the complete.dsw workspace located in the top level directory. This workspace contains the source for the two sample applications and the crashrpt library. You only need to build the crashrpt project—crashrpt.dsp.

Note: CrashRpt library uses the WTL for its GUI components, so WTL must be installed and properly configured in order to build the CrashRpt library. You can download the WTL files from http://www.microsoft.com/downloads/details.aspx?FamilyID=128e26ee-2112-4cf7-b28e-7727d9a1f288&DisplayLang=en. If you're new to the WTL here is a good place to start http://www.clipcode.net/content/wtl_guide/chapter1.htm.

Note: CrashRpt library uses Microsoft's Debug Help library (dbghelp.dll). The proper h and lib files must be installed and properly configured in order to build the CrashRpt library. These files are availble in the Debugging SDK, which can be downloaded here http://www.microsoft.com/ddk/debugging/default.asp (be sure to select the SDK setup option).

After the build completes, you should end up with the following:

crashrpt\include
  crashrpt.h
crashrpt\bin\debug or crashrpt\bin\release
  crashrpt.dll
crashrpt\lib
  crashrpt.lib
crashrpt\src
  [all source files...]

Linking against the library

To implicitly link against the library, you need to include the crashrpt.h file and link in the crashrpt.lib file. I find it easiest to add the following two lines to my main application file.

#include "[whateveryourpath]/crashrpt/include/crashrpt.h"
#pragma comment(lib, "[whateveryourpath]/crashrpt/lib/crashrpt")

Figure 3—Integrating CrashRpt with your application

Initializing the library

The library needs to be initialized before it will catch any exceptions. You do this by calling the Install method, usually from your main function. The Install method is detailed below.

//---------------------------------------------------------------
// Install
//    Initializes the library and optionally set the client crash
//     callback andset up the email details.
//
// Parameters
//    pfn         Client crash callback
//    lpTo        Email address to send crash report
//    lpSubject   Subject line to be used with email
//
// Return Values
//    If the function succeeds, the return value is a pointer
//    to the underlying crash object created. This state
//    information is required as the first parameter to all
//    other crash report functions.
//
// Remarks
//    Passing NULL for lpTo will disable the email feature and
//    cause the crash report to be saved to disk.
//
CRASHRPTAPI
LPVOID
Install(
  IN LPGETLOGFILE pfn OPTIONAL,          // client crash callback
  IN LPCTSTR lpTo OPTIONAL,              // Email:to
  IN LPCTSTR lpSubject OPTIONAL          // Email:subject
  );

Figure 4—The Install() function

All of the parameters are optional. The first parameter is a pointer to a crash callback function defined as:

// Client crash callback
typedef BOOL (CALLBACK *LPGETLOGFILE) (LPVOID lpvState);

Figure 5—Client crash callback

You would define this callback only if you wanted to be notified of an application failure so you could perform some basic clean up (such as close db connections, attempt to save, and so forth). Otherwise, you can simply pass NULL for this parameter.

The second parameter defines the e-mail address you want the crash report mailed to, or NULL if you prefer the reports be saved to the user's workstation.

The third parameter is the subject line used in the generated mail message.

The Install function returns a pointer to the underlying object that implements the real functionality of this library. This value is required for all subsequent calls into the library.

If, after you have called Install, you decide to unhook the crashrpt library, you would call Uninstall.

//---------------------------------------------------------------
// Uninstall
//    Uninstalls the unhandled exception filter set up in
//    Install().
//
// Parameters
//    lpState     State information returned from Install()
//
// Return Values
//    void
//
// Remarks
//    This call is optional. The crash report library will
//    automatically deinitialize when the library is unloaded.
//    Call this function to unhook the exception filter manually.
//
CRASHRPTAPI
void
Uninstall(
   IN LPVOID lpState              // State from Install()
   );

Figure 6—The Uninstall function

You would only ever call Uninstall if you decided, after calling Install, that you did not want the crashrpt library to intercept exceptions. So, basically you will probably never call this method directly.

Adding custom files to the report

The client application can, at any time, supply files to be included in the crash report by calling the AddFile function.

//---------------------------------------------------------------
// AddFile
//    Adds a file to the crash report.
//
// Parameters
//    lpState     State information returned from Install()
//    lpFile      Fully qualified file name
//    lpDesc      Description of file, used by details dialog
//
// Return Values
//    void
//
// Remarks
//    This function can be called anytime after Install()
//    to add one or more files to the generated crash report.
//
CRASHRPTAPI
void
AddFile(
  IN LPVOID lpState,                      // State from Install()
  IN LPCTSTR lpFile,                      // File name
  IN LPCTSTR lpDesc                       // File desc
  );

Figure 7—The AddFile functionp

This is useful when your application uses or produces external files such as initialization files or log files. When a report is generated, it will include these additional files.

Manually generating a report

You can force report generation by calling the GenerateErrorReport. This is useful when you want to provide an easy way to gather debugging information about your application to help debug a non-fatal bug.

//---------------------------------------------------------------
// GenerateErrorReport
//    Generates the crash report.
//
// Parameters
//    lpState     State information returned from Install()
//    pExInfo     Pointer to an EXCEPTION_POINTERS structure
//
// Return Values
//    void
//
// Remarks
//    Call this function to manually generate a crash report.
//
CRASHRPTAPI
void
GenerateErrorReport(
  IN LPVOID lpState,
  IN PEXCEPTION_POINTERS pExInfo OPTIONAL
  );

Figure 8—The GenerateErrorReport function

If you do not supply a valid EXCEPTION_POINTERS structure, the minidump callstack may be incomplete.

Generate debug symbols

To get the most out of the minidump, the debugger needs your application's debug symbols. By default, release builds don't generate debug symbols. You can configure VC to generate debug symbols for release builds by changing a couple of project settings.

With the release build configuration selected, on the C/C++ tab under the General category, select 'Program Database' under Debug info.

Click here for a larger image.

Figure 9a—C++ Project Settings

On the Link tab under the General category, check the 'Generate debug info' option.

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Figure 9b—Link Project Settings

Now, release builds will generate debug symbols in a PDB file. Keep all executables and PDB files for each release that ships to customers. You will need these files to read minidump files in the debugger.

Using the Crash Report

Using the Crash Log

The crash log is an XML file that describes details about the crash including the type of exception, the module and offset where the exception occurred, as well as some cursory operating system and hardware information. I wrote the crash log to make it easier to catalog crashes. A crash can be uniquely identified by the module, offset, and exception code. This information could be inspected by a developer, or an automated process, and compared against previously reported problems. If a match is found, the developer, or automated process, could inform the user of the solution without having to debug the error again.

The log is divided into four different sections or nodes. The first node is ExceptionRecord, which we discussed earlier.

Figure 10—ExceptionRecord Node

Next is the Processor node, which contains a little information about the user's CPU.

Figure 11—Process Node

Next is the OperatingSystem node, which contains the user's operating system version information.

Figure 12—OperatingSystem Node

Last is the Modules node. This node contains the path, version, base address, size, and time stamp for every module loaded by the deceased application.

Figure 13—Modules Node

Using the Crash Dump File

The crash dump file is a minidump created with the help of the DbgHelp DLL's MiniDumpWriteDump function. The minidump contains various information about the state of the application when the error occurred including the call stack, local variables, and loaded modules. For more on creating minidumps check out Andy Pennell's article.

You can view minidump files in VS.NET or the WinDbg debugger. Because WinDbg is free, I'll use it in the following example. You can download WinDbg from http://www.microsoft.com/ddk/debugging/default.asp. I'm using version 6.1.0017.0 in the example.

The sample application included with this article does nothing but generate a null pointer exception. I'll use the sample to generate a crash and demonstrate how to use the resulting minidump.

When you run the sample application, click on the bomb button to generate a null pointer exception, and save the resulting crash report. Then, extract the crash.dmp file from the crash report, launch WinDbg, and open the crash dump by pressing CTRL+D.

Next you need to set the symbol path for WinDbg with the .sympath command. Switch to the command window (ALT+1) and enter .sympath followed by a space followed by the semi-colon delimited list of directories to search.

.sympath c:\downloads\CrashRptTest

Figure 14—Setting the symbol path

Similarly, you need to set the executable and source search paths with the .exepath and .srcpath commands.

.exepath c:\downloads\CrashRptTest
.srcpath c:\downloads\CrashRptTest

Figure 15—Setting the source and executable paths

The final step is to change the debugger context to the context record associated with the exception by entering the .ecxr command.

.ecxr

Figure 15—Setting the exception context record

If everything is configured correctly, you should now be able to walk the call stack, and see local variables and loaded modules. You can even have WinDbg highlight the offending line of code by double-clicking the CrashRptTest frame in the Call Stack window (ALT+6). Note: The exact line number may be a little off due to linker optimizations.

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