[Bug other/46770] Replace .ctors/.dtors with .init_array/.fini_array on targets supporting them

["ppluzhnikov at google dot com" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46770

--- Comment #76 from Paul Pluzhnikov <ppluzhnikov at google dot com> 2012-04-17 15:18:56 UTC ---
(In reply to comment #75)

> Can you provide a testcase?

// foo.h
struct Foo {
  Foo(Foo *other) : x(other->x) { }
  Foo() : x(42) { }

  int x;

private:
  Foo(const Foo&);
};

extern Foo foo_global;

// foo.cc
#include "foo.h"
Foo foo_global;

// main.cc
#include <assert.h>
#include "foo.h"

Foo foo(&foo_global);

int main() { assert(foo.x == 42); }


Above, foo.cc simulates a library, and main depends on that library having been
initialized.

Using pre-init_array GCC, this works:

  g++ main.cc foo.cc && a.out

and this doesn't:

  g++ foo.cc main.cc && ./a.out
  a.out: main.cc:6: int main(): Assertion `foo.x == 42' failed.

Using post-init_array GCC, the behavior is reversed: natural link order
(libraries after main) is broken.

> ARM EABI has been using .init_array from day
> one.  How does it work for ARM EABI?

It doesn't. We have a *lot* of programs that don't run on ARM though, and they
are all broken by this change.

Note: we do understand that the example above depends on undefined behavior,
and we do intend to eventually fix our source. But it will take a lot of
effort.