(* *********************************************************************)
(*                                                                     *)
(*              The Compcert verified compiler                         *)
(*                                                                     *)
(*          Xavier Leroy, INRIA Paris-Rocquencourt                     *)
(*                                                                     *)
(*  Copyright Institut National de Recherche en Informatique et en     *)
(*  Automatique.  All rights reserved.  This file is distributed       *)
(*  under the terms of the INRIA Non-Commercial License Agreement.     *)
(*                                                                     *)
(* *********************************************************************)
(** Machine- and ABI-dependent layout information for activation records. *)
(** In the PowerPC/EABI application binary interface, the general shape of activation records is as follows, from bottom (lowest offsets) to top: - 8 reserved bytes.  The first 4 bytes hold the back pointer to the activation record of the caller.  The next 4 bytes are reserved for called functions to store their return addresses. Since we would rather store our return address in our own frame, we will not use these 4 bytes, and just reserve them. - Space for outgoing arguments to function calls. - Local stack slots. - Saved values of callee-save registers used by the function. - Space for the stack-allocated data declared in Cminor.  The [frame_env] compilation environment records the positions of the boundaries between areas in the frame part. *)
Definition fe_ofs_arg := 8.
(** Computation of the frame environment from the bounds of the current function. *)
Definition make_env (b: bounds) :=
let ol := align (8 + 4 * b.(bound_outgoing)) 8 in    (* locals *)
let ora := ol + 4 * b.(bound_local) in (* saved return address *)
let ocs := ora + 4 in            (* callee-saves *)
let oendcs := size_callee_save_area b ocs in
let ostkdata := align oendcs 8 in (* stack data *)
let sz := align (ostkdata + b.(bound_stack_data)) 16 in
{| fe_size := sz;
fe_ofs_link := 0;
fe_ofs_retaddr := ora;
fe_ofs_local := ol;
fe_ofs_callee_save := ocs;
fe_stack_data := ostkdata;
fe_used_callee_save := b.(used_callee_save) |}.
(** Separation property *)
Local Open Scope sep_scope.

Lemma frame_env_aligned:
forall b,
let fe := make_env b in
(8 | fe_ofs_arg)
/\ (8 | fe_ofs_local fe)
/\ (8 | fe_stack_data fe)
/\ (4 | fe_ofs_link fe)
/\ (4 | fe_ofs_retaddr fe).