Generating a Dump File

Generating a dump file when a program crashes in Windows using C++ can be quite useful for debugging purposes. Here's a general approach to achieve this:

1. Using Windows Error Reporting (WER)

Windows Error Reporting (WER): Windows has built-in support for creating dump files when applications crash. You can configure WER to generate these files automatically.
Registry Settings: You can use the Windows Registry to configure WER settings for your application. The key to look at is HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\Windows Error Reporting\LocalDumps. Here, you can set the path for dump files, the type of dump, and other options.
Dump Type: You can specify the type of dump you want to create - mini, full, or custom. A mini dump contains minimal information like the stack trace, while a full dump has complete information about the application's memory.

Using Custom Exception Handlers

SetUnhandledExceptionFilter: In your C++ code, you can use the SetUnhandledExceptionFilter function to set a custom exception handler. This handler can be used to create a dump file when an unhandled exception occurs.
MiniDumpWriteDump Function: Within your custom exception handler, you can use the MiniDumpWriteDump function from the DbgHelp library to create the dump file. This function allows you to specify what to include in the dump.

Example Code:

#include <Windows.h>
#include <DbgHelp.h>

LONG WINAPI UnhandledExceptionFilter(EXCEPTION_POINTERS* pExceptionPointers) {
    HANDLE hDumpFile = CreateFile(L"CrashDump.dmp", GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);

    if (hDumpFile != INVALID_HANDLE_VALUE) {
        MINIDUMP_EXCEPTION_INFORMATION dumpInfo;
        dumpInfo.ExceptionPointers = pExceptionPointers;
        dumpInfo.ThreadId = GetCurrentThreadId();
        dumpInfo.ClientPointers = TRUE;

        MiniDumpWriteDump(GetCurrentProcess(), GetCurrentProcessId(), hDumpFile, MiniDumpNormal, &dumpInfo, NULL, NULL);
        CloseHandle(hDumpFile);
    }

    return EXCEPTION_EXECUTE_HANDLER;
}

int main() {
    SetUnhandledExceptionFilter(UnhandledExceptionFilter);
    // Your code here
    return 0;
}

In this code, UnhandledExceptionFilter is a custom function that creates a dump file named "CrashDump.dmp" when an unhandled exception occurs.

Considerations

Privacy and Security: Dump files can contain sensitive data. Ensure you handle them securely and comply with any relevant privacy laws or guidelines.
Distribution Size: Including DbgHelp library functions can increase the size of your application's distribution.
Testing: Thoroughly test the dump file generation on different Windows versions and configurations to ensure reliability.

Remember that automatically generating dump files is primarily a development and debugging tool. For production environments, ensure that this behavior is consistent with your application's error handling and user experience strategy.

2. Using Linux

Creating automatic crash dump files in Linux with C++ is slightly different from Windows. In Linux, you typically use core dumps for this purpose. A core dump is a file that records the memory image of a process at the time of its crash, which can be later analyzed to understand the state of the program when it failed.

Enabling Core Dumps

Check Current Core Dump Settings: First, you should check the current core dump configuration on your Linux system. Use the command ulimit -c in the terminal. If it returns 0, core dumps are disabled.
Enable Core Dumps: To enable core dumps, you can set the core file size limit to unlimited by using ulimit -c unlimited. This change is temporary and only applies to the current shell session. To make it permanent, you should modify relevant configuration files like /etc/security/limits.conf.
Configuring Core Dump Location: By default, core dumps are created in the directory where the program crashed. You can change the location and name of the core dump files by setting the core_pattern in /proc/sys/kernel/core_pattern.

For instance my core_pattern is:

|/usr/share/apport/apport -p%p -s%s -c%c -d%d -P%P -u%u -g%g -- %E

Let's break down the components of your pattern /usr/share/apport/apport -p%p -s%s -c%c -d%d -P%P -u%u -g%g -- %E:

/usr/share/apport/apport: This indicates that core dumps are being handled by apport, which is a tool used on some Linux distributions (like Ubuntu) for automatically reporting bugs. When a crash occurs, apport is invoked to handle the core dump.
The remaining part of the pattern consists of various options passed to apport:
- -p%p: This option passes the PID (Process ID) of the crashing process to apport.
- -s%s: Passes the signal number that caused the crash.
- -c%c: Passes the core dump file (or its size).
- -d%d: Passes the UNIX timestamp of when the crash occurred.
- -P%P: Passes the PID of the parent process.
- -u%u: Passes the real UID (User ID) of the crashing process.
- -g%g: Passes the real GID (Group ID) of the crashing process.
- -- %E: %E is a placeholder for the executable path. The -- separates the options from the executable path.

When using apport on systems like Ubuntu, the core dump files are handled differently compared to the traditional method of directly generating a core file in the current directory of the crashed process. Here's how to understand where your core dump might be and its naming convention:

Locating the Core Dump

Default Behavior with Apport: When apport handles a crash, it typically doesn't leave a core dump file in a user-accessible location immediately. Instead, it collects data about the crash and can create a report in /var/crash/.
Check /var/crash/: Look in the /var/crash/ directory for files related to your application. Files here are named using the pattern _executable_path_pid_date-time.crash, where executable_path is the path to the crashed application, pid is the process ID, and date-time is the timestamp of the crash.
Reports instead of Core Dumps: The files in /var/crash/ are not traditional core dumps but rather contain information gathered by apport, which can include stack traces, application-specific details, and sometimes excerpts of memory content.

Extracting Core Dump from Apport Reports

If you need an actual core dump file for debugging with tools like GDB, you might need to extract it from the apport report or change the core dump handling configuration.
In some cases, you can find a core dump embedded within the .crash file in /var/crash/. You can extract it using a tool like apport-retrace.

Enabling Traditional Core Dumps

If you prefer traditional core dump files, you can disable apport or change the core_pattern back to a simpler form like core or /tmp/core.%e.%p.
To do this, you can modify /proc/sys/kernel/core_pattern. Be cautious with this, as changing system-level configurations can have broader implications.

Permissions and Access

Remember that core dump files and apport reports might be created with permissions that restrict access to root or certain user groups. You may need superuser privileges to access them.

By default, on systems using apport, you won't find a traditional core file like you might expect on other Unix/Linux systems. Instead, look for the apport crash reports in /var/crash/, and if necessary, adjust your system's core dump handling configuration based on your needs.

to get some info regarding the cump file:

cat /var/log/apport.log

which in my cases is:

ERROR: apport (pid 12408) Tue Nov 14 23:12:52 2023: executable does not belong to a package, ignoring
ERROR: apport (pid 12408) Tue Nov 14 23:12:52 2023: writing core dump to core._home_behnam_workspace_cpp_tutorials_build_Debug_core_dump.1000.05385b29-05e0-4187-8afe-eb0b6fa44f14.12407.305836 (limit: -1)

Based on the log entry from /var/log/apport.log, it appears that apport did not generate a crash report in /var/crash/ because the executable that crashed did not belong to an installed package. apport typically generates crash reports for packages that are part of the system's package management, and it often ignores crashes from executables that are not part of such packages (like locally compiled programs).

However, the log also indicates that a core dump was written. Here's how to interpret the information:

Core Dump Location and Name: The log mentions that the core dump is being written to a file named core._home_behnam_workspace_cpp_tutorials_build_Debug_core_dump.1000.05385b29-05e0-4187-8afe-eb0b6fa44f14.12407.305836. This suggests that the core dump file is being created with a specific naming pattern.
Understanding the Filename:
- The part core indicates it's a core dump.
- _home_behnam_workspace_cpp_tutorials_build_Debug_core_dump suggests the path or identifier of the executable.
- 1000 is likely the user ID (UID) under which the process was running.
- The long alphanumeric string (05385b29-05e0-4187-8afe-eb0b6fa44f14) could be a unique identifier for the crash instance.
- 12407 is likely the PID (Process ID) of the crashed process.
- The final number sequence (305836) could be a timestamp or another identifier related to the crash.
Locating the Core Dump File: The log does not specify the absolute path to where this core dump file is written. It could be in the working directory of the crashed process or a system-defined location for core dumps (often /var/lib/apport/coredump or a similar directory). You can search for this file using the find command:
```
sudo find / -name "core._home_behnam_workspace_cpp_tutorials_build_Debug_core_dump*"
```
This command searches the entire file system for a file name starting with core._home_behnam_workspace_cpp_tutorials_build_Debug_core_dump, so modify the search pattern if necessary.

In my case its was under:

/var/lib/apport/coredump

Permissions: You might need superuser privileges to access or search for the core dump file.
Analyzing the Core Dump: Once you locate the core dump file, you can analyze it using a debugger like GDB for more insights into the cause of the crash.

Remember that handling and analyzing core dumps can require careful consideration, especially regarding system security and data privacy.

Using Signal Handlers in C++

Signal Handler: In your C++ code, you can set up a custom signal handler for segmentation faults (SIGSEGV) and other signals that indicate a crash.
Register the Handler: Use the signal() or sigaction() functions to register your custom signal handler.
Generate Core Dump Within Handler: While you can't directly create a core dump within a signal handler, you can ensure that the normal core dump process happens. For instance, you can log additional information or clean up resources before the crash.

Example Code

#include <signal.h>
#include <unistd.h>
#include <stdlib.h>
#include <iostream>

void signalHandler(int signum) {
    std::cout << "Caught signal " << signum << ", generating core dump." << std::endl;
    // Perform cleanup or logging if necessary
    signal(signum, SIG_DFL); // Reset to default handler
    raise(signum); // Generate core dump
}

int main() {
    signal(SIGSEGV, signalHandler);
    // Your code here

    // Example: cause segmentation fault for demonstration
    int *p = nullptr;
    *p = 10;

    return 0;
}

Analyzing Core Dumps

To analyze the generated core dump, you can use a debugger like GDB. For instance, gdb <executable> <core dump> will allow you to inspect the state of the program at the crash.

Considerations

Size and Security: Core dumps can be large and contain sensitive data. Ensure they are stored securely and managed according to your data handling policies.
Distribution Impact: If you're distributing a C++ application, ensure your users are aware of how to enable core dumps and where they will be located.
Automated Reporting: Consider implementing a mechanism for automatically reporting crashes, which might include sending core dumps or extracted information to a server for analysis.

Remember, enabling core dumps is typically used in development and testing phases. In production environments, ensure that handling of core dumps is aligned with your application's stability, security, and user experience strategies.

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generating_and_debugging_dump_file.md

generating_and_debugging_dump_file.md

Generating a Dump File

1. Using Windows Error Reporting (WER)

Using Custom Exception Handlers

Considerations

2. Using Linux

Enabling Core Dumps

Locating the Core Dump

Extracting Core Dump from Apport Reports

Enabling Traditional Core Dumps

Permissions and Access

Using Signal Handlers in C++

Example Code

Analyzing Core Dumps

Considerations

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generating_and_debugging_dump_file.md

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generating_and_debugging_dump_file.md

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Generating a Dump File

1. Using Windows Error Reporting (WER)

Using Custom Exception Handlers

Considerations

2. Using Linux

Enabling Core Dumps

Locating the Core Dump

Extracting Core Dump from Apport Reports

Enabling Traditional Core Dumps

Permissions and Access

Using Signal Handlers in C++

Example Code

Analyzing Core Dumps

Considerations