Overview

Crash upload component helps in uploading the crashes (coredump or minidump files) that happened in the set-top boxes to the crash portal server(which can be configured). Crash portal collects crash dumps and logs which happened in the connected STBs, process these and provide a meaningful backtrace.

Crash Portal server processes 2 types of crash dump files

Minidumps

• Minidump files are a lightweight crash dump format developed by Microsoft.
• Google Breakpad project supplies tools to work with Minidump files.
• The primary tool used by Crash Portal is minidump_stackwalk which generates a stack trace from a minidump file.
• See http://www.chromium.org/developers/decoding-crash-dumps

Coredumps

• Coredump files are standard Linux coredumps.
• Crash Portal extracts information from the coredump files but does not generate a stack trace.
  • But a tool such as gdb will do this.

CrashUpload

Minidump or core files are tarred and uploaded by crashUpload component:

  https://code.rdkcentral.com/r/rdk/components/generic/crashupload

dump-backup.service invokes /lib/rdk/core_shell.sh which is responsible for calling uploadDumps.sh script to upload the crash dump to crash portal server.

echo "|$RDK_PATH/core_shell.sh %e %s %t" >/proc/sys/kernel/core_pattern

uploadDumps.sh script collects the following and compresses it to create a .tgz format

• minidump file (*.dmp)
• version.txt
• ocapri_log.txt
• messages.txt
• core_log.txt

Minidump

• A list of the executable and shared libraries that were loaded in the process at the time the dump was created. This list includes both file names and identifiers for the particular versions of those files that were loaded.
• A list of threads present in the process. For each thread, the minidump includes the state of the processor registers, and the contents of the threads' stack memory.
• Other information about the system on which the dump was collected: processor and operating system versions, the reason for the dump, and so on. 

Google Breakpad

Breakpad is a library that records crashes in compact "minidump" files. It  produce C and C++ stack traces from minidumps. Breakpad can also write minidumps on request for programs that have not crashed. 

How to Integrate Google Breakpad library?

• Link against libbreakpad_client library.

• #include "client/linux/handler/exception_handler.h“

• Instantiate an ExceptionHandler object, ExceptionHandler constructor requires a path where it can write minidumps, as well as a callback function to receive information about minidumps that were written.

#include "client/linux/handler/exception_handler.h“ // Include Header file for exception handler
static bool dumpCallback(const google_breakpad::MinidumpDescriptor& descriptor, void* context, bool succeeded)
{
  printf("Dump path: %s\n", descriptor.path());
  return succeeded;
}

int main(int argc, char* argv[])
{
  google_breakpad::MinidumpDescriptor descriptor("/tmp"); 
  google_breakpad::ExceptionHandler eh(descriptor, // Minidump will be saved in /tmp
                                       NULL,
                                       dumpCallback, //Callback
                                       NULL,
                                       true,

Google Breakpad Utilities

• dump_syms is used for symbol extraction.

• minidump_stackwalk is used for  symbolized stack trace 

uploadDumps.sh collects core dumps/ mini dumps  to crash server whenever any applications crashes.

Sample Application

#include "client/linux/handler/exception_handler.h“
static bool dumpCallback(const google_breakpad::MinidumpDescriptor& descriptor,
                         void* context,
                         bool succeeded)
{
  printf("Dump path: %s\n", descriptor.path());
  return succeeded;
}

void crash()
{
  volatile int* a = (int*)(NULL);
  *a = 1;
}


int main(int argc, char* argv[])
{
  google_breakpad::MinidumpDescriptor descriptor("/tmp");
  google_breakpad::ExceptionHandler eh(descriptor,
                                       NULL,
                                       dumpCallback,
                                       NULL,
                                       true,
                                       -1);
  crash();
  return 0;
}

To compile the source

• Create a simple Makefile
• Add the following contents to the Makefile

• make 

Execute the sample application

• An application of name “breakpad_exercise” will be generated. Copy this executable to the box 
• Run the application in the box which will cause segmentation fault:

• A minidump will be generated in the same file

Coredump

Core dump files generated after an uncaught signal in a process (as a SIGSEGV or SIGQUIT), are generated in the base directory where the program was executed, and the core dumps starts with the name  as “core” or “core.PID”.

By default size of the core will be zero, To generate the core, we need to set the size of the core to unlimited. 

• ulimit -c unlimited

By default, core will be generated in the current directory with the file name "core". We can change the core generating directory from current directory to another by editing the kernel configuration file core pattern(/proc/sys/kernel/core_pattern)  in the kernel.

• echo "newpattern" > /proc/sys/kernel/core_pattern

Core pattern is helpful in the case if there are couple of core dumps files in one directory and we don't know which program caused it.

How to get stack trace?

Make sue the executable is compiled with -g option to turn on the debugging symbols

gdb <executable_path> <coredump_file_path>

(gdb) bt full