On Linux, backtrace_symbols_fd function doesn't work as expected

Question

I referred to this Stack Overflow question to test if SIGSEGV could be caught and processed:

How to automatically generate a stacktrace when my program crashes

File h.cpp

#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 = 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);
}

int main()
{
  int *foo = (int*)-1;  // Make a bad pointer
  printf("%d\n", *foo); // Causes a segmentation fault
}

I compile them:

gcc -rdynamic -g h.cpp && ./a.out

Result:

Segmentation fault (core dump)

Well, it doesn't print out the call stack as I expected. Do I have to set up any system parameters?

you don't register signal handler use `signal(SIGSEGV, handler);` in the main function for install handler. — sorosh_sabz, Sep 30 '16 at 10:38

score 2 · Accepted Answer · answered Sep 30 '16 at 10:43

There are two problems.

A SIGSEGV handler is not registered using sigaction().
Within the signal handler, fprintf is called. fprintf is not a reentrant library function, and it cannot be called from a signal handler. Especially for a SIGSEGV when, potentially, the entire heap has been nuked from high orbit, and stderrs, internal file buffer could be a smoking crater. Only system calls, like write() can be safely called from a signal handler.

score 1 · Answer 2 · edited Oct 15 '21 at 15:53

1

Change the main function like below:

int main()
{
   signal(SIGSEGV, handler);  // Register handler
   int *foo = (int*)-1;  // Make a bad pointer
   printf("%d\n", *foo);  // Causes a segmentation fault
}

edited Oct 15 '21 at 15:53

Peter Mortensen

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answered Sep 30 '16 at 10:42

sorosh_sabz

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1

`signal()` is obsolete. All new code should use `sigaction()`. – Sam Varshavchik Sep 30 '16 at 11:22

On Linux, backtrace_symbols_fd function doesn't work as expected

File h.cpp

2 Answers2