al_uninstall_system excutes a function called "shutdown" if present

no-reply@allegro.cc (Roy Balela) — Sat, 28 Jul 2018 00:05:27 +0000

I was experiencing some random crashes when uninstalling Allegro.

I found out that if I have a function called shutdown(), al_uninstall_system will execute it twice when called.

I'm compiling with GCC on Linux. Compiling with G++ does not reproduce the error.

Allegro v5.2.4.1
GCC v4.8.4
Linux v3.13.0-37

If I rename the function, no error or warnings are emitted.

The code below runs fine, but shutdown() is called twice when Allegro is uninstalled.

#SelectExpand
  1#include 
  2#include 
  3#include 
  4#include 
  5
  6ALLEGRO_DISPLAY *display;
  7ALLEGRO_FONT *font;
  8
  9void abort_on_error(const char *message) {
 10  fprintf(stderr, "%s\n", message);
 11  exit(EXIT_FAILURE);
 12}
 13
 14void setup() {
 15  if (!al_install_system(ALLEGRO_VERSION_INT, NULL))
 16    abort_on_error("Failed to init Allegro");
 17  
 18  display = al_create_display(320, 240);
 19  if (!display) abort_on_error("Failed to create window");
 20
 21  al_set_window_title(display, "Allegro Test");
 22  
 23  font = al_create_builtin_font();
 24  if (!font) abort_on_error("Failed to create font");
 25}
 26
 27void shutdown() {
 28  printf("Calling shutdown()\n");
 29}
 30
 31void real_shutdown() {
 32  al_destroy_font(font);
 33  al_destroy_display(display);
 34  printf("al_uninstall_system() start\n");
 35  al_uninstall_system();
 36  printf("al_uninstall_system() end\n");
 37}
 38
 39void play() {
 40  al_clear_to_color(al_map_rgb_f(0,0,0));
 41  al_draw_text(font, al_map_rgb_f(1,1,1), 10, 10, 0, "Allegro Test");
 42  al_flip_display();
 43  al_rest(2);
 44}
 45
 46int main (int argc, char *argv[]) {
 47  setup();
 48  play();
 49  real_shutdown();
 50  return 0;
 51}

Output:

al_uninstall_system() start
Calling shutdown()
Calling shutdown()
al_uninstall_system() end

no-reply@allegro.cc (DanielH) — Sat, 28 Jul 2018 00:31:58 +0000

Am I blind, but when do you call "void shutdown()"?

I see you're program prints "Calling shutdown()", but it was never called.

no-reply@allegro.cc (torhu) — Sat, 28 Jul 2018 00:45:16 +0000

Just put a breakpoint on shutdown() to see where it is being called from?

As you probably know you would normally just call al_init, not al_install_system or al_uninstall_system.

no-reply@allegro.cc (Edgar Reynaldo) — Sat, 28 Jul 2018 00:49:16 +0000

It's a linking bug. Allegro sees your shutdown function and calls it mistakenly, thinking it is its own version of shutdown.

You can debug this easily by setting a breakpoint in your shutdown function. Then when allegro calls it, gdb will stop and let you get a backtrace. Do it twice. Post the results.

no-reply@allegro.cc (Roy Balela) — Sat, 28 Jul 2018 01:22:59 +0000

Backtrace:

#0  shutdown () at test.c:28
#1  0x00007ffff5de0786 in xcb_disconnect ()
   from /usr/lib/x86_64-linux-gnu/libxcb.so.1
#2  0x00007ffff6caf4e7 in XCloseDisplay ()
   from /usr/lib/x86_64-linux-gnu/libX11.so.6
#3  0x00007ffff7b77a17 in ?? ()
   from /usr/lib/x86_64-linux-gnu/liballegro.so.5.2
#4  0x00007ffff7b2bcd5 in ?? ()
   from /usr/lib/x86_64-linux-gnu/liballegro.so.5.2
#5  0x00007ffff7b1fd4d in _al_run_exit_funcs ()
   from /usr/lib/x86_64-linux-gnu/liballegro.so.5.2
#6  0x00007ffff7b2bdb5 in al_uninstall_system ()
   from /usr/lib/x86_64-linux-gnu/liballegro.so.5.2
#7  0x0000000000400c89 in real_shutdown () at test.c:35
#8  0x0000000000400da5 in main (argc=1, argv=0x7fffffffe158) at test.c:49

Edgar Reynaldo said:

It's a linking bug. Allegro sees your shutdown function and calls it mistakenly, thinking it is its own version of shutdown.

Apparently, yes. I just found out shutdown() is POSIX function(https://linux.die.net/man/2/shutdown), so I better not have another function with the same name.

Thank you!