SPARC stack layout

[Sven Panne]

[ I know that this is not the perfect place to ask, because the
  question in not very Haskell-related, but I know that there are a
  few good SPARC hackers on this list and the GCC lists looks a bit
  crowded, so I'll try here first... :-]

While figuring out the stack layout on SPARC (System V ABI v8) using
GCC, I stumbled over a strange thing: Directly below the frame pointer
%fp GCC leaves 16 bytes space, so the whole stack frame is always
16-20 bytes (depending on alignment) larger than it needs to be,
e.g. a C/C++ function without any local variables needs 112 bytes stack,
not 92, as I expected. A quick look into the SPARC part of the GCC
sources, namely gcc-3.0.2/gcc/config/sparc/sparc.h, leads to the
conclusion that this space is for a "long double", e.g. the stack
frame for

   int foo(int a, int b) {
      return a+b;
   }

looks like the one I expected for

   int foo(int a, int b) {
      long double _DONT_KNOW_WHAT_THIS_IS_;
      return a+b;
   }

But why does *every* C/C++ function need such a buffer? Any clues?

Perplexed,
   S.
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