/* Copyright 2001,2009-2015,2018,2025
     Free Software Foundation, Inc.

   This file is part of Guile.

   Guile is free software: you can redistribute it and/or modify it
   under the terms of the GNU Lesser General Public License as published
   by the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   Guile is distributed in the hope that it will be useful, but WITHOUT
   ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
   License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with Guile.  If not, see
   <https://www.gnu.org/licenses/>.  */

#ifndef _SCM_FRAMES_H_
#define _SCM_FRAMES_H_

#include <string.h>

#include <libguile/gc.h>


/* Stack frames
   ------------

   It's a little confusing, but there are two representations of frames
   in this file: frame pointers, and Scheme objects wrapping those frame
   pointers.  The former uses the SCM_FRAME macro prefix, the latter
   SCM_VM_FRAME prefix.

   The confusing thing is that only Scheme frame objects have functions
   that use them, and they use the lower-case scm_frame prefix.


   Stack frame layout
   ------------------

   | ...                          |
   +==============================+ <- fp + 3 = SCM_FRAME_PREVIOUS_SP (fp)
   | Dynamic link                 |
   +------------------------------+
   | Virtual return address (vRA) |
   +------------------------------+
   | Machine return address (mRA) |
   +==============================+ <- fp
   | Local 0                      |
   +------------------------------+
   | Local 1                      |
   +------------------------------+
   | ...                          |
   +------------------------------+
   | Local N-1                    |
   \------------------------------/ <- sp

   The stack grows down.

   The calling convention is that a caller prepares a stack frame
   consisting of the saved FP, the saved virtual return address, and the
   saved machine return address of the calling function, followed by the
   procedure and then the arguments to the call, in order.  Thus in the
   beginning of a call, the procedure being called is in slot 0, the
   first argument is in slot 1, and the SP points to the last argument.
   The number of arguments, including the procedure, is thus FP - SP.

   After ensuring that the correct number of arguments have been passed,
   a function will set the stack pointer to point to the last local
   slot.  This lets a function allocate the temporary space that it
   needs once in the beginning of the call, instead of pushing and
   popping the stack pointer during the call's extent.

   When a program returns, it returns its values in the slots starting
   from local 0.  The callee resets the stack pointer to point to the
   last value.  In this way the caller knows how many values there are:
   it's the number of words between the stack pointer and the slot at
   which the caller placed the procedure.

   After checking that the number of values returned is appropriate, the
   caller shuffles the values around (if needed), and resets the stack
   pointer back to its original value from before the call.  */




/* Each element on the stack occupies the same amount of space.  */
union scm_vm_stack_element
{
  uintptr_t as_uint;
  uint32_t *as_vcode;
  uint8_t *as_mcode;
  SCM as_scm;
  double as_f64;
  uint64_t as_u64;
  int64_t as_s64;

  /* For GC purposes.  */
  void *as_ptr;
  scm_t_bits as_bits;
};

#define SCM_FRAME_PREVIOUS_SP(fp)	((fp) + 3)
#define SCM_FRAME_MACHINE_RETURN_ADDRESS(fp)         ((fp)[0].as_mcode)
#define SCM_FRAME_SET_MACHINE_RETURN_ADDRESS(fp, ra) ((fp)[0].as_mcode = (ra))
#define SCM_FRAME_VIRTUAL_RETURN_ADDRESS(fp)         ((fp)[1].as_vcode)
#define SCM_FRAME_SET_VIRTUAL_RETURN_ADDRESS(fp, ra) ((fp)[1].as_vcode = (ra))
#define SCM_FRAME_DYNAMIC_LINK(fp)      ((fp) + (fp)[2].as_uint)
#define SCM_FRAME_SET_DYNAMIC_LINK(fp, dl) ((fp)[2].as_uint = ((dl) - (fp)))
#define SCM_FRAME_SLOT(fp,i)            ((fp) - (i) - 1)
#define SCM_FRAME_LOCAL(fp,i)           (SCM_FRAME_SLOT (fp, i)->as_scm)
#define SCM_FRAME_NUM_LOCALS(fp, sp)    ((fp) - (sp))


/*
 * Heap frames
 */

SCM_API SCM scm_frame_p (SCM obj);
SCM_API SCM scm_frame_procedure_name (SCM frame);
SCM_API SCM scm_frame_call_representation (SCM frame);
SCM_API SCM scm_frame_arguments (SCM frame);
SCM_API SCM scm_frame_source (SCM frame);
SCM_API SCM scm_frame_address (SCM frame);
SCM_API SCM scm_frame_stack_pointer (SCM frame);
SCM_API SCM scm_frame_instruction_pointer (SCM frame);
SCM_API SCM scm_frame_return_address (SCM frame);
SCM_API SCM scm_frame_dynamic_link (SCM frame);
SCM_API SCM scm_frame_previous (SCM frame);

#endif /* _SCM_FRAMES_H_ */