1.8.6: gc.c and __builtin_frame_pointer

I'm playing with porting Ruby to Stratus VOS, which is an unusual but
POSIX-supporting x86 platform.

My first build problem was a crash in miniruby, in gc.c.  In a nutshell,
gc.c is relying on __builtin_frame_pointer but is not setting
-fno-omit-frame-pointer.  This causes a crash, but I'm not sure what the
proper semantics of these two are and if I should (a) submit a patch for
Ruby in autoconf, or (b) submit a patch to Stratus for a bug in their gcc
implementation (currently at 3.3.1).

Details:

gc.c, post-preprocessor, looks like this:

  __attribute__ ((noinline)) static VALUE * stack_end_address(void)
    { return (VALUE *) __builtin_frame_address(0); }
  typedef unsigned long VALUE;
...
  static void garbage_collect() {
    VALUE *stack_end = stack_end_address();
...
  rb_gc_mark_locations((VALUE*)(stack_end), rb_gc_stack_start);
...
  }
  void rb_gc_mark_locations(start, end)                           
    VALUE *start, *end;
...

Somehow, this ends up calling rb_gc_mark_locations with a weird stack_end:

#1  0x0003c98b in rb_gc_mark_locations (
    start=0x172378,
    end=0x40010ee0)
    at gc.c:642
#2  0x0003ddff in garbage_collect ()
    at gc.c:1368

(gdb) f 1
(gdb) p start
$3 = (VALUE *) 0x1000
(gdb) p &start
Address requested for identifier "start" which is in register $edx

Even though stack_end itself looks reasonable:

(gdb) f 2
#2  0x0003ddff in garbage_collect ()
    at gc.c:1368
1368     rb_gc_mark_locations((VALUE*)STACK_END, rb_gc_stack_start);
(gdb) p stack_end
$3 = (
    VALUE *) 0x400eb8d0

Now, I would *think* that either you have frame pointers, or you don't.
And, looking at stack_end, we seem to - but we can't seem to pass it
anywhere.

OTOH, I imagine that calling __builtin_frame_pointer but defining
-fomit-frame-pointer is "undefined behavior".

On the third hand, I see at least one package (kaffe) has moved away from
__builtin_frame_pointer in favor of "some assember" due to GCC bugs.

Anyone know a few things about this?

-- 
Jay Levitt                |
Boston, MA                | My character doesn't like it when they
Faster: jay at jay dot fm | cry or shout or hit.
http://www.jay.fm         | - Kristoffer