Opensource contributions by locations



Opensource Contributions by locations





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Getting backtrace during stack corruption

As we know , if program crashes and if it results in stack corruption, GDB will never give backtrace of the crashes.Even coredump does not help. Consider the below situation of stack corruption, Is it possible to make out anything useful from this for debugging?No Program received signal SIGSEGV , Segmentation fault . 0x00000002 in ?? () ( gdb ) bt #0 0x00000002 in ?? () #1 0x00000001 in ?? () #2 0xbffff284 in ?? () Backtrace stopped : previous frame inner to this frame ( corrupt stack ?) ( gdb ) Those bogus adresses (0x00000002 and the like) are actually PC values, not SP values. Now, when you get this kind of SEGV, with a bogus (very small) PC address, 99% of the time it's due to calling through a bogus function pointer. Note that virtual calls in C++ are implemented via function pointers, so any problem with a virtual call can manifest in the same way. An indirect call instruction just pushes the PC after the call onto the stack and then sets the PC
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Analyzing Crash dumps in Linux using GDB

GDB is a common tool for debugging applications in Linux development environment. Before generating the core dump use -g compiler option for compiling the application for enabling debugging symbols. 1. set ulimit -c unlimited  in cmd to enable core dump. 2. Then run the application, after application crashes it generates code dump with core.pid file name. 3. Load the application in gdb ex: gdb <path to application> 4. In this step load the core dump by using core-file <path to core dump> command 5.Just use bt for getting the backtrace of the crash which will give you exact location where app has crashed. Use GDB instead of logging which will save your time for debugging !!!!
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Generate backtrace automatically when program crashes due to SIGSEGV

For Linux and I believe Mac OS X, if you're using gcc, or any compiler that uses glibc, you can use the backtrace() functions in execinfo.h to print a stacktrace and exit gracefully when you get a segmentation fault. Documentation can be found in the libc manual. Here's an example program that installs a SIGSEGV handler and prints a stacktrace to stderr when it segfaults. The baz() function here causes the segfault that triggers the handler: #include <stdio.h> #include <execinfo.h> #include <signal.h> #include <stdlib.h> #include <unistd.h> void handler(int sig) {   void *array[10];   size_t size;   // get void*'s for all entries on the stack   size = backtrace(array, 10);   // print out all the frames to stderr   fprintf(stderr, "Error: signal %d:\n", sig);   backtrace_symbols_fd(array, size, STDERR_FILENO);   exit(1); } void baz() {  int *foo = (int*)-1; // make a bad pointer   printf("%d\n", *
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