Open Radar

 
Executables can declare a set of entries to be run before (constructors) and after (destructors) the main body of code.

These entries are placed into special sections in the executable designated .mod_init_func  and .mod_term_func respectively.

in the example code we declare a startup function (__attribute__((constructor))) and a 
shutdown (__attribute__((destructor)).

==== ctor-dtor.c

#include <stdio.h>

__attribute__((constructor))
void startup ()
{
  fprintf(stderr, "startup\n");
}


__attribute__((destructor))
void shutdown ()
{
  fprintf(stderr, "shutdown\n");
}


int main ()
{
  printf ("42\n");
  return 0;
}

=====


On MacOS 11.6 and earlier, the output is:
startup
42
shutdown

On MacOS 12.0 the output is:
startup
42

==== so the destructor is not called.

NOTE: this does NOT show when the compiler is clang since clang attaches destructors to "cxa_atexit()" instead of using the mod term section.