Question

I am working on Linux with the GCC compiler. When my C++ program crashes I would like it to automatically generate a stacktrace.

My program is being run by many different users and it also runs on Linux, Windows and Macintosh (all versions are compiled using gcc).

I would like my program to be able to generate a stack trace when it crashes and the next time the user runs it, it will ask them if it is ok to send the stack trace to me so I can track down the problem. I can handle the sending the info to me but I don’t know how to generate the trace string. Any ideas?

Answer 1

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', *foo);       // causes segfault }  void bar() { baz(); } void foo() { bar(); }   int main(int argc, char **argv) {   signal(SIGSEGV, handler);   // install our handler   foo(); // this will call foo, bar, and baz.  baz segfaults. } 

Compiling with -g -rdynamic gets you symbol info in your output, which glibc can use to make a nice stacktrace:

$ gcc -g -rdynamic ./test.c -o test 

Executing this gets you this output:

$ ./test Error: signal 11: ./test(handler+0x19)[0x400911] /lib64/tls/libc.so.6[0x3a9b92e380] ./test(baz+0x14)[0x400962] ./test(bar+0xe)[0x400983] ./test(foo+0xe)[0x400993] ./test(main+0x28)[0x4009bd] /lib64/tls/libc.so.6(__libc_start_main+0xdb)[0x3a9b91c4bb] ./test[0x40086a] 

This shows the load module, offset, and function that each frame in the stack came from. Here you can see the signal handler on top of the stack, and the libc functions before main in addition to main, foo, bar, and baz.