guile/libguile/foreign.c

/* Copyright (C) 2010-2013  Free Software Foundation, Inc.
 *
 * This library 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.
 *
 * This library 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 this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301 USA
 */

#if HAVE_CONFIG_H
#  include <config.h>
#endif

#include <ffi.h>

#include <alloca.h>
#include <alignof.h>
#include <string.h>
#include <assert.h>

#include "libguile/_scm.h"
#include "libguile/bytevectors.h"
#include "libguile/instructions.h"
#include "libguile/threads.h"
#include "libguile/foreign.h"



SCM_SYMBOL (sym_void, "void");
SCM_SYMBOL (sym_float, "float");
SCM_SYMBOL (sym_double, "double");
SCM_SYMBOL (sym_uint8, "uint8");
SCM_SYMBOL (sym_int8, "int8");
SCM_SYMBOL (sym_uint16, "uint16");
SCM_SYMBOL (sym_int16, "int16");
SCM_SYMBOL (sym_uint32, "uint32");
SCM_SYMBOL (sym_int32, "int32");
SCM_SYMBOL (sym_uint64, "uint64");
SCM_SYMBOL (sym_int64, "int64");
SCM_SYMBOL (sym_short, "short");
SCM_SYMBOL (sym_int, "int");
SCM_SYMBOL (sym_long, "long");
SCM_SYMBOL (sym_unsigned_short, "unsigned-short");
SCM_SYMBOL (sym_unsigned_int, "unsigned-int");
SCM_SYMBOL (sym_unsigned_long, "unsigned-long");
SCM_SYMBOL (sym_size_t, "size_t");
SCM_SYMBOL (sym_ssize_t, "ssize_t");
SCM_SYMBOL (sym_ptrdiff_t, "ptrdiff_t");

/* that's for pointers, you know. */
SCM_SYMBOL (sym_asterisk, "*");

SCM_SYMBOL (sym_null, "%null-pointer");
SCM_SYMBOL (sym_null_pointer_error, "null-pointer-error");

/* The cell representing the null pointer.  */
static SCM null_pointer;


/* Raise a null pointer dereference error.  */
static void
null_pointer_error (const char *func_name)
{
  scm_error (sym_null_pointer_error, func_name,
	     "null pointer dereference", SCM_EOL, SCM_EOL);
}


static SCM cif_to_procedure (SCM cif, SCM func_ptr);


static SCM pointer_weak_refs = SCM_BOOL_F;


static void
register_weak_reference (SCM from, SCM to)
{
  scm_weak_table_putq_x (pointer_weak_refs, from, to);
}

static void
pointer_finalizer_trampoline (void *ptr, void *data)
{
  scm_t_pointer_finalizer finalizer = data;
  finalizer (SCM_POINTER_VALUE (SCM_PACK_POINTER (ptr)));
}

SCM_DEFINE (scm_pointer_p, "pointer?", 1, 0, 0,
	    (SCM obj),
	    "Return @code{#t} if @var{obj} is a pointer object, "
	    "@code{#f} otherwise.\n")
#define FUNC_NAME s_scm_pointer_p
{
  return scm_from_bool (SCM_POINTER_P (obj));
}
#undef FUNC_NAME

SCM_DEFINE (scm_make_pointer, "make-pointer", 1, 1, 0,
	    (SCM address, SCM finalizer),
	    "Return a foreign pointer object pointing to @var{address}. "
	    "If @var{finalizer} is passed, it should be a pointer to a "
	    "one-argument C function that will be called when the pointer "
	    "object becomes unreachable.")
#define FUNC_NAME s_scm_make_pointer
{
  void *c_finalizer;
  scm_t_uintptr c_address;

  c_address = scm_to_uintptr_t (address);
  if (SCM_UNBNDP (finalizer))
    c_finalizer = NULL;
  else
    {
      SCM_VALIDATE_POINTER (2, finalizer);
      c_finalizer = SCM_POINTER_VALUE (finalizer);
    }

  return scm_from_pointer ((void *) c_address, c_finalizer);
}
#undef FUNC_NAME

void *
scm_to_pointer (SCM pointer)
#define FUNC_NAME "scm_to_pointer"
{
  SCM_VALIDATE_POINTER (1, pointer);
  return SCM_POINTER_VALUE (pointer);
}
#undef FUNC_NAME

SCM
scm_from_pointer (void *ptr, scm_t_pointer_finalizer finalizer)
{
  SCM ret;

  if (ptr == NULL && finalizer == NULL)
    ret = null_pointer;
  else
    {
      ret = scm_cell (scm_tc7_pointer, (scm_t_bits) ptr);

      if (finalizer)
        scm_i_set_finalizer (SCM2PTR (ret), pointer_finalizer_trampoline,
                             finalizer);
    }

  return ret;
}

SCM_DEFINE (scm_pointer_address, "pointer-address", 1, 0, 0,
	    (SCM pointer),
	    "Return the numerical value of @var{pointer}.")
#define FUNC_NAME s_scm_pointer_address
{
  SCM_VALIDATE_POINTER (1, pointer);

  return scm_from_uintptr_t ((scm_t_uintptr) SCM_POINTER_VALUE (pointer));
}
#undef FUNC_NAME

SCM_DEFINE (scm_pointer_to_scm, "pointer->scm", 1, 0, 0,
	    (SCM pointer),
	    "Unsafely cast @var{pointer} to a Scheme object.\n"
	    "Cross your fingers!")
#define FUNC_NAME s_scm_pointer_to_scm
{
  SCM_VALIDATE_POINTER (1, pointer);
  
  return SCM_PACK ((scm_t_bits) SCM_POINTER_VALUE (pointer));
}
#undef FUNC_NAME

SCM_DEFINE (scm_scm_to_pointer, "scm->pointer", 1, 0, 0,
	    (SCM scm),
	    "Return a foreign pointer object with the @code{object-address}\n"
            "of @var{scm}.")
#define FUNC_NAME s_scm_scm_to_pointer
{
  SCM ret;

  ret = scm_from_pointer ((void*) SCM_UNPACK (scm), NULL);
  if (SCM_HEAP_OBJECT_P (ret))
    register_weak_reference (ret, scm);

  return ret;
}
#undef FUNC_NAME

SCM_DEFINE (scm_pointer_to_bytevector, "pointer->bytevector", 2, 2, 0,
	    (SCM pointer, SCM len, SCM offset, SCM uvec_type),
	    "Return a bytevector aliasing the @var{len} bytes pointed\n"
	    "to by @var{pointer}.\n\n"
            "The user may specify an alternate default interpretation for\n"
            "the memory by passing the @var{uvec_type} argument, to indicate\n"
            "that the memory is an array of elements of that type.\n"
            "@var{uvec_type} should be something that\n"
            "@code{uniform-vector-element-type} would return, like @code{f32}\n"
            "or @code{s16}.\n\n"
	    "When @var{offset} is passed, it specifies the offset in bytes\n"
	    "relative to @var{pointer} of the memory region aliased by the\n"
	    "returned bytevector.")
#define FUNC_NAME s_scm_pointer_to_bytevector
{
  SCM ret;
  scm_t_int8 *ptr;
  size_t boffset, blen;
  scm_t_array_element_type btype;

  SCM_VALIDATE_POINTER (1, pointer);
  ptr = SCM_POINTER_VALUE (pointer);

  if (SCM_UNLIKELY (ptr == NULL))
    null_pointer_error (FUNC_NAME);

  if (SCM_UNBNDP (uvec_type))
    btype = SCM_ARRAY_ELEMENT_TYPE_VU8;
  else
    {
      int i;
      for (i = 0; i <= SCM_ARRAY_ELEMENT_TYPE_LAST; i++)
        if (scm_is_eq (uvec_type, scm_i_array_element_types[i]))
          break;
      switch (i)
        {
        case SCM_ARRAY_ELEMENT_TYPE_VU8:
        case SCM_ARRAY_ELEMENT_TYPE_U8:
        case SCM_ARRAY_ELEMENT_TYPE_S8:
        case SCM_ARRAY_ELEMENT_TYPE_U16:
        case SCM_ARRAY_ELEMENT_TYPE_S16:
        case SCM_ARRAY_ELEMENT_TYPE_U32:
        case SCM_ARRAY_ELEMENT_TYPE_S32:
        case SCM_ARRAY_ELEMENT_TYPE_U64:
        case SCM_ARRAY_ELEMENT_TYPE_S64:
        case SCM_ARRAY_ELEMENT_TYPE_F32:
        case SCM_ARRAY_ELEMENT_TYPE_F64:
        case SCM_ARRAY_ELEMENT_TYPE_C32:
        case SCM_ARRAY_ELEMENT_TYPE_C64:
          btype = i;
          break;
        default:
          scm_wrong_type_arg_msg (FUNC_NAME, SCM_ARG1, uvec_type,
                                  "uniform vector type");
        }
    }

  if (SCM_UNBNDP (offset))
    boffset = 0;
  else
    boffset = scm_to_size_t (offset);

  blen = scm_to_size_t (len);

  ret = scm_c_take_typed_bytevector ((signed char *) ptr + boffset,
				     blen, btype, pointer);

  return ret;
}
#undef FUNC_NAME

SCM_DEFINE (scm_bytevector_to_pointer, "bytevector->pointer", 1, 1, 0,
	    (SCM bv, SCM offset),
	    "Return a pointer pointer aliasing the memory pointed to by\n"
            "@var{bv} or @var{offset} bytes after @var{bv} when @var{offset}\n"
	    "is passed.")
#define FUNC_NAME s_scm_bytevector_to_pointer
{
  SCM ret;
  signed char *ptr;
  size_t boffset;

  SCM_VALIDATE_BYTEVECTOR (1, bv);
  ptr = SCM_BYTEVECTOR_CONTENTS (bv);

  if (SCM_UNBNDP (offset))
    boffset = 0;
  else
    boffset = scm_to_unsigned_integer (offset, 0,
                                       SCM_BYTEVECTOR_LENGTH (bv) - 1);

  ret = scm_from_pointer (ptr + boffset, NULL);
  register_weak_reference (ret, bv);
  return ret;
}
#undef FUNC_NAME

SCM_DEFINE (scm_set_pointer_finalizer_x, "set-pointer-finalizer!", 2, 0, 0,
            (SCM pointer, SCM finalizer),
            "Arrange for the C procedure wrapped by @var{finalizer} to be\n"
            "called on the pointer wrapped by @var{pointer} when @var{pointer}\n"
            "becomes unreachable. Note: the C procedure should not call into\n"
            "Scheme. If you need a Scheme finalizer, use guardians.")
#define FUNC_NAME s_scm_set_pointer_finalizer_x
{
  SCM_VALIDATE_POINTER (1, pointer);
  SCM_VALIDATE_POINTER (2, finalizer);

  scm_i_add_finalizer (SCM2PTR (pointer), pointer_finalizer_trampoline,
                       SCM_POINTER_VALUE (finalizer));

  return SCM_UNSPECIFIED;
}
#undef FUNC_NAME

void
scm_i_pointer_print (SCM pointer, SCM port, scm_print_state *pstate)
{
  scm_puts_unlocked ("#<pointer 0x", port);
  scm_uintprint (scm_to_uintptr_t (scm_pointer_address (pointer)), 16, port);
  scm_putc_unlocked ('>', port);
}


/* Non-primitive helpers functions.  These procedures could be
   implemented in terms of the primitives above but would be inefficient
   (heap allocation overhead, Scheme/C round trips, etc.)  */

SCM_DEFINE (scm_dereference_pointer, "dereference-pointer", 1, 0, 0,
	    (SCM pointer),
	    "Assuming @var{pointer} points to a memory region that\n"
	    "holds a pointer, return this pointer.")
#define FUNC_NAME s_scm_dereference_pointer
{
  void **ptr;

  SCM_VALIDATE_POINTER (1, pointer);

  ptr = SCM_POINTER_VALUE (pointer);
  if (SCM_UNLIKELY (ptr == NULL))
    null_pointer_error (FUNC_NAME);

  return scm_from_pointer (*ptr, NULL);
}
#undef FUNC_NAME

SCM_DEFINE (scm_string_to_pointer, "string->pointer", 1, 1, 0,
	    (SCM string, SCM encoding),
	    "Return a foreign pointer to a nul-terminated copy of\n"
	    "@var{string} in the given @var{encoding}, defaulting to\n"
            "the current locale encoding.  The C string is freed when\n"
            "the returned foreign pointer becomes unreachable.\n\n"
            "This is the Scheme equivalent of @code{scm_to_stringn}.")
#define FUNC_NAME s_scm_string_to_pointer
{
  SCM_VALIDATE_STRING (1, string);

  /* XXX: Finalizers slow down libgc; they could be avoided if
     `scm_to_string' & co. were able to use libgc-allocated memory.  */

  if (SCM_UNBNDP (encoding))
    return scm_from_pointer (scm_to_locale_string (string), free);
  else
    {
      char *enc;
      SCM ret;
      
      SCM_VALIDATE_STRING (2, encoding);

      enc = scm_to_locale_string (encoding);
      scm_dynwind_begin (0);
      scm_dynwind_free (enc);

      ret = scm_from_pointer
        (scm_to_stringn (string, NULL, enc,
                         scm_i_default_port_conversion_handler ()),
         free);

      scm_dynwind_end ();

      return ret;
    }
}
#undef FUNC_NAME

SCM_DEFINE (scm_pointer_to_string, "pointer->string", 1, 2, 0,
	    (SCM pointer, SCM length, SCM encoding),
	    "Return the string representing the C string pointed to by\n"
            "@var{pointer}.  If @var{length} is omitted or @code{-1}, the\n"
            "string is assumed to be nul-terminated.  Otherwise\n"
            "@var{length} is the number of bytes in memory pointed to by\n"
            "@var{pointer}.  The C string is assumed to be in the given\n"
            "@var{encoding}, defaulting to the current locale encoding.\n\n"
	    "This is the Scheme equivalent of @code{scm_from_stringn}.")
#define FUNC_NAME s_scm_pointer_to_string
{
  size_t len;

  SCM_VALIDATE_POINTER (1, pointer);

  if (SCM_UNBNDP (length)
      || scm_is_true (scm_eqv_p (length, scm_from_int (-1))))
    len = (size_t)-1;
  else
    len = scm_to_size_t (length);
    
  if (SCM_UNBNDP (encoding))
    return scm_from_locale_stringn (SCM_POINTER_VALUE (pointer), len);
  else
    {
      char *enc;
      SCM ret;
      
      SCM_VALIDATE_STRING (3, encoding);

      enc = scm_to_locale_string (encoding);
      scm_dynwind_begin (0);
      scm_dynwind_free (enc);

      ret = scm_from_stringn (SCM_POINTER_VALUE (pointer), len, enc,
                              scm_i_default_port_conversion_handler ());

      scm_dynwind_end ();

      return ret;
    }
}
#undef FUNC_NAME



SCM_DEFINE (scm_alignof, "alignof", 1, 0, 0, (SCM type),
            "Return the alignment of @var{type}, in bytes.\n\n"
            "@var{type} should be a valid C type, like @code{int}.\n"
            "Alternately @var{type} may be the symbol @code{*}, in which\n"
            "case the alignment of a pointer is returned. @var{type} may\n"
            "also be a list of types, in which case the alignment of a\n"
            "@code{struct} with ABI-conventional packing is returned.")
#define FUNC_NAME s_scm_alignof
{
  if (SCM_I_INUMP (type))
    {
      switch (SCM_I_INUM (type))
        {
        case SCM_FOREIGN_TYPE_FLOAT:
          return scm_from_size_t (alignof_type (float));
        case SCM_FOREIGN_TYPE_DOUBLE:
          return scm_from_size_t (alignof_type (double));
        case SCM_FOREIGN_TYPE_UINT8:
          return scm_from_size_t (alignof_type (scm_t_uint8));
        case SCM_FOREIGN_TYPE_INT8:
          return scm_from_size_t (alignof_type (scm_t_int8));
        case SCM_FOREIGN_TYPE_UINT16:
          return scm_from_size_t (alignof_type (scm_t_uint16));
        case SCM_FOREIGN_TYPE_INT16:
          return scm_from_size_t (alignof_type (scm_t_int16));
        case SCM_FOREIGN_TYPE_UINT32:
          return scm_from_size_t (alignof_type (scm_t_uint32));
        case SCM_FOREIGN_TYPE_INT32:
          return scm_from_size_t (alignof_type (scm_t_int32));
        case SCM_FOREIGN_TYPE_UINT64:
          return scm_from_size_t (alignof_type (scm_t_uint64));
        case SCM_FOREIGN_TYPE_INT64:
          return scm_from_size_t (alignof_type (scm_t_int64));
        default:
          scm_wrong_type_arg (FUNC_NAME, 1, type);
        }
    }
  else if (scm_is_eq (type, sym_asterisk))
    /* a pointer */
    return scm_from_size_t (alignof_type (void*));
  else if (scm_is_pair (type))
    {
      /* TYPE is a structure.  Section 3-3 of the i386, x86_64, PowerPC,
	 and SPARC P.S. of the System V ABI all say: "Aggregates
	 (structures and arrays) and unions assume the alignment of
	 their most strictly aligned component."  */
      size_t max;

      for (max = 0; scm_is_pair (type); type = SCM_CDR (type))
	{
	  size_t align;

	  align = scm_to_size_t (scm_alignof (SCM_CAR (type)));
	  if (align  > max)
	    max = align;
	}

      return scm_from_size_t (max);
    }
  else
    scm_wrong_type_arg (FUNC_NAME, 1, type);
}
#undef FUNC_NAME

SCM_DEFINE (scm_sizeof, "sizeof", 1, 0, 0, (SCM type),
            "Return the size of @var{type}, in bytes.\n\n"
            "@var{type} should be a valid C type, like @code{int}.\n"
            "Alternately @var{type} may be the symbol @code{*}, in which\n"
            "case the size of a pointer is returned. @var{type} may also\n"
            "be a list of types, in which case the size of a @code{struct}\n"
            "with ABI-conventional packing is returned.")
#define FUNC_NAME s_scm_sizeof
{
  if (SCM_I_INUMP (type))
    {
      switch (SCM_I_INUM (type))
        {
        case SCM_FOREIGN_TYPE_FLOAT:
          return scm_from_size_t (sizeof (float));
        case SCM_FOREIGN_TYPE_DOUBLE:
          return scm_from_size_t (sizeof (double));
        case SCM_FOREIGN_TYPE_UINT8:
          return scm_from_size_t (sizeof (scm_t_uint8));
        case SCM_FOREIGN_TYPE_INT8:
          return scm_from_size_t (sizeof (scm_t_int8));
        case SCM_FOREIGN_TYPE_UINT16:
          return scm_from_size_t (sizeof (scm_t_uint16));
        case SCM_FOREIGN_TYPE_INT16:
          return scm_from_size_t (sizeof (scm_t_int16));
        case SCM_FOREIGN_TYPE_UINT32:
          return scm_from_size_t (sizeof (scm_t_uint32));
        case SCM_FOREIGN_TYPE_INT32:
          return scm_from_size_t (sizeof (scm_t_int32));
        case SCM_FOREIGN_TYPE_UINT64:
          return scm_from_size_t (sizeof (scm_t_uint64));
        case SCM_FOREIGN_TYPE_INT64:
          return scm_from_size_t (sizeof (scm_t_int64));
        default:
          scm_wrong_type_arg (FUNC_NAME, 1, type);
        }
    }
  else if (scm_is_eq (type, sym_asterisk))
    /* a pointer */
    return scm_from_size_t (sizeof (void*));
  else if (scm_is_pair (type))
    {
      /* a struct */
      size_t off = 0;
      size_t align = scm_to_size_t (scm_alignof(type));
      while (scm_is_pair (type))
        {
          off = ROUND_UP (off, scm_to_size_t (scm_alignof (scm_car (type))));
          off += scm_to_size_t (scm_sizeof (scm_car (type)));
          type = scm_cdr (type);
        }
      return scm_from_size_t (ROUND_UP(off, align));
    }
  else
    scm_wrong_type_arg (FUNC_NAME, 1, type);
}
#undef FUNC_NAME


/* return 1 on success, 0 on failure */
static int
parse_ffi_type (SCM type, int return_p, long *n_structs, long *n_struct_elts)
{
  if (SCM_I_INUMP (type))
    {
      if ((SCM_I_INUM (type) < 0 )
          || (SCM_I_INUM (type) > SCM_FOREIGN_TYPE_LAST))
        return 0;
      else if (SCM_I_INUM (type) == SCM_FOREIGN_TYPE_VOID && !return_p)
        return 0;
      else
        return 1;
    }
  else if (scm_is_eq (type, sym_asterisk))
    /* a pointer */
    return 1;
  else
    {
      long len;
      
      len = scm_ilength (type);
      if (len < 1)
        return 0;
      while (len--)
        {
          if (!parse_ffi_type (scm_car (type), 0, n_structs, n_struct_elts))
            return 0;
          (*n_struct_elts)++;
          type = scm_cdr (type);
        }
      (*n_structs)++;
      return 1;
    }
}
    
static void
fill_ffi_type (SCM type, ffi_type *ftype, ffi_type ***type_ptrs,
               ffi_type **types)
{
  if (SCM_I_INUMP (type))
    {
      switch (SCM_I_INUM (type))
        {
        case SCM_FOREIGN_TYPE_FLOAT:
          *ftype = ffi_type_float;
          return;
        case SCM_FOREIGN_TYPE_DOUBLE:
          *ftype = ffi_type_double;
          return;
        case SCM_FOREIGN_TYPE_UINT8:
          *ftype = ffi_type_uint8;
          return;
        case SCM_FOREIGN_TYPE_INT8:
          *ftype = ffi_type_sint8;
          return;
        case SCM_FOREIGN_TYPE_UINT16:
          *ftype = ffi_type_uint16;
          return;
        case SCM_FOREIGN_TYPE_INT16:
          *ftype = ffi_type_sint16;
          return;
        case SCM_FOREIGN_TYPE_UINT32:
          *ftype = ffi_type_uint32;
          return;
        case SCM_FOREIGN_TYPE_INT32:
          *ftype = ffi_type_sint32;
          return;
        case SCM_FOREIGN_TYPE_UINT64:
          *ftype = ffi_type_uint64;
          return;
        case SCM_FOREIGN_TYPE_INT64:
          *ftype = ffi_type_sint64;
          return;
        case SCM_FOREIGN_TYPE_VOID:
          *ftype = ffi_type_void;
          return;
        default:
          scm_wrong_type_arg_msg ("pointer->procedure", 0, type,
                                  "foreign type");
        }
    }
  else if (scm_is_eq (type, sym_asterisk))
    /* a pointer */
    {
      *ftype = ffi_type_pointer;
      return;
    }
  else
    {
      long i, len;
      
      len = scm_ilength (type);

      ftype->size = 0;
      ftype->alignment = 0;
      ftype->type = FFI_TYPE_STRUCT;
      ftype->elements = *type_ptrs;
      *type_ptrs += len + 1;

      for (i = 0; i < len; i++)
        {
          ftype->elements[i] = *types;
          *types += 1;
          fill_ffi_type (scm_car (type), ftype->elements[i],
                         type_ptrs, types);
          type = scm_cdr (type);
        }
      ftype->elements[i] = NULL;
    }
}

/* Return a "cif" (call interface) for the given RETURN_TYPE and
   ARG_TYPES.  */
static ffi_cif *
make_cif (SCM return_type, SCM arg_types, const char *caller)
#define FUNC_NAME caller
{
  SCM walk;
  long i, nargs, n_structs, n_struct_elts;
  size_t cif_len;
  char *mem;
  ffi_cif *cif;
  ffi_type **type_ptrs;
  ffi_type *types;

  nargs = scm_ilength (arg_types);
  SCM_ASSERT (nargs >= 0, arg_types, 3, FUNC_NAME);
  /* fixme: assert nargs < 1<<32 */
  n_structs = n_struct_elts = 0;

  /* For want of talloc, we're going to have to do this in two passes: first we
     figure out how much memory is needed for all types, then we allocate the
     cif and the types all in one block. */
  if (!parse_ffi_type (return_type, 1, &n_structs, &n_struct_elts))
    scm_wrong_type_arg (FUNC_NAME, 1, return_type);
  for (walk = arg_types; scm_is_pair (walk); walk = scm_cdr (walk))
    if (!parse_ffi_type (scm_car (walk), 0, &n_structs, &n_struct_elts))
      scm_wrong_type_arg (FUNC_NAME, 3, scm_car (walk));

  /* the memory: with space for the cif itself */
  cif_len = sizeof (ffi_cif);

  /* then ffi_type pointers: one for each arg, one for each struct
     element, and one for each struct (for null-termination) */
  cif_len = (ROUND_UP (cif_len, alignof_type (void *))
	     + (nargs + n_structs + n_struct_elts)*sizeof(void*));

  /* then the ffi_type structs themselves, one per arg and struct element, and
     one for the return val */
  cif_len = (ROUND_UP (cif_len, alignof_type (ffi_type))
	     + (nargs + n_struct_elts + 1)*sizeof(ffi_type));

  mem = scm_gc_malloc_pointerless (cif_len, "foreign");
  /* ensure all the memory is initialized, even the holes */
  memset (mem, 0, cif_len);
  cif = (ffi_cif *) mem;

  /* reuse cif_len to walk through the mem */
  cif_len = ROUND_UP (sizeof (ffi_cif), alignof_type (void *));
  type_ptrs = (ffi_type**)(mem + cif_len);
  cif_len = ROUND_UP (cif_len
		      + (nargs + n_structs + n_struct_elts)*sizeof(void*),
		      alignof_type (ffi_type));
  types = (ffi_type*)(mem + cif_len);

  /* whew. now knit the pointers together. */
  cif->rtype = types++;
  fill_ffi_type (return_type, cif->rtype, &type_ptrs, &types);
  cif->arg_types = type_ptrs;
  type_ptrs += nargs;
  for (walk = arg_types, i = 0; scm_is_pair (walk); walk = scm_cdr (walk), i++)
    {
      cif->arg_types[i] = types++;
      fill_ffi_type (scm_car (walk), cif->arg_types[i], &type_ptrs, &types);
    }

  /* round out the cif, and we're done. */
  cif->abi = FFI_DEFAULT_ABI;
  cif->nargs = nargs;
  cif->bytes = 0;
  cif->flags = 0;

  if (FFI_OK != ffi_prep_cif (cif, FFI_DEFAULT_ABI, cif->nargs, cif->rtype,
			      cif->arg_types))
    SCM_MISC_ERROR ("ffi_prep_cif failed", SCM_EOL);

  return cif;
}
#undef FUNC_NAME

SCM_DEFINE (scm_pointer_to_procedure, "pointer->procedure", 3, 0, 0,
            (SCM return_type, SCM func_ptr, SCM arg_types),
            "Make a foreign function.\n\n"
            "Given the foreign void pointer @var{func_ptr}, its argument and\n"
            "return types @var{arg_types} and @var{return_type}, return a\n"
            "procedure that will pass arguments to the foreign function\n"
            "and return appropriate values.\n\n"
            "@var{arg_types} should be a list of foreign types.\n"
            "@code{return_type} should be a foreign type.")
#define FUNC_NAME s_scm_pointer_to_procedure
{
  ffi_cif *cif;

  SCM_VALIDATE_POINTER (2, func_ptr);

  cif = make_cif (return_type, arg_types, FUNC_NAME);

  return cif_to_procedure (scm_from_pointer (cif, NULL), func_ptr);
}
#undef FUNC_NAME



/* We support calling foreign functions with up to 100 arguments. */

#define CODE(nreq)                                                  \
  SCM_PACK_OP_24 (assert_nargs_ee, nreq + 1),                       \
  SCM_PACK_OP_12_12 (foreign_call, 0, 1)

#define CODE_10(n)                                                      \
  CODE (n + 0), CODE (n + 1), CODE (n + 2), CODE (n + 3), CODE (n + 4), \
  CODE (n + 5), CODE (n + 6), CODE (n + 7), CODE (n + 8), CODE (n + 9)

static const scm_t_uint32 foreign_stub_code[] =
  {
    CODE_10 (0), CODE_10 (10), CODE_10 (20), CODE_10 (30), CODE_10 (40),
    CODE_10 (50), CODE_10 (60), CODE_10 (70), CODE_10 (80), CODE_10 (90)
  };

#undef CODE
#undef CODE_10

static const scm_t_uint32 *
get_foreign_stub_code (unsigned int nargs)
{
  if (nargs >= 100)
    scm_misc_error ("make-foreign-function", "args >= 100 currently unimplemented",
                    SCM_EOL);

  return &foreign_stub_code[nargs * 2];
}

/* Given a foreign procedure, determine its minimum arity. */
int
scm_i_foreign_arity (SCM foreign, int *req, int *opt, int *rest)
{
  const scm_t_uint32 *code = SCM_PROGRAM_CODE (foreign);

  if (code < foreign_stub_code)
    return 0;
  if (code > (foreign_stub_code
              + (sizeof(foreign_stub_code) / sizeof(scm_t_uint32))))
    return 0;

  *req = (code - foreign_stub_code) / 2;
  *opt = 0;
  *rest = 0;

  return 1;
}

static SCM
cif_to_procedure (SCM cif, SCM func_ptr)
{
  ffi_cif *c_cif;
  SCM ret;
  scm_t_bits nfree = 2;
  scm_t_bits flags = SCM_F_PROGRAM_IS_FOREIGN;

  c_cif = (ffi_cif *) SCM_POINTER_VALUE (cif);

  ret = scm_words (scm_tc7_program | (nfree << 16) | flags, nfree + 2);
  SCM_SET_CELL_WORD_1 (ret, get_foreign_stub_code (c_cif->nargs));
  SCM_PROGRAM_FREE_VARIABLE_SET (ret, 0, cif);
  SCM_PROGRAM_FREE_VARIABLE_SET (ret, 1, func_ptr);
  
  return ret;
}

/* Set *LOC to the foreign representation of X with TYPE.  */
static void
unpack (const ffi_type *type, void *loc, SCM x, int return_value_p)
#define FUNC_NAME "scm_i_foreign_call"
{
  switch (type->type)
    {
    case FFI_TYPE_FLOAT:
      *(float *) loc = scm_to_double (x);
      break;
    case FFI_TYPE_DOUBLE:
      *(double *) loc = scm_to_double (x);
      break;

    /* For integer return values smaller than `int', libffi expects the
       result in an `ffi_arg'-long buffer.  */

    case FFI_TYPE_UINT8:
      if (return_value_p)
	*(ffi_arg *) loc = scm_to_uint8 (x);
      else
	*(scm_t_uint8 *) loc = scm_to_uint8 (x);
      break;
    case FFI_TYPE_SINT8:
      if (return_value_p)
	*(ffi_arg *) loc = scm_to_int8 (x);
      else
	*(scm_t_int8 *) loc = scm_to_int8 (x);
      break;
    case FFI_TYPE_UINT16:
      if (return_value_p)
	*(ffi_arg *) loc = scm_to_uint16 (x);
      else
	*(scm_t_uint16 *) loc = scm_to_uint16 (x);
      break;
    case FFI_TYPE_SINT16:
      if (return_value_p)
	*(ffi_arg *) loc = scm_to_int16 (x);
      else
	*(scm_t_int16 *) loc = scm_to_int16 (x);
      break;
    case FFI_TYPE_UINT32:
      if (return_value_p)
	*(ffi_arg *) loc = scm_to_uint32 (x);
      else
	*(scm_t_uint32 *) loc = scm_to_uint32 (x);
      break;
    case FFI_TYPE_SINT32:
      if (return_value_p)
	*(ffi_arg *) loc = scm_to_int32 (x);
      else
	*(scm_t_int32 *) loc = scm_to_int32 (x);
      break;
    case FFI_TYPE_UINT64:
      *(scm_t_uint64 *) loc = scm_to_uint64 (x);
      break;
    case FFI_TYPE_SINT64:
      *(scm_t_int64 *) loc = scm_to_int64 (x);
      break;
    case FFI_TYPE_STRUCT:
      SCM_VALIDATE_POINTER (1, x);
      memcpy (loc, SCM_POINTER_VALUE (x), type->size);
      break;
    case FFI_TYPE_POINTER:
      SCM_VALIDATE_POINTER (1, x);
      *(void **) loc = SCM_POINTER_VALUE (x);
      break;
    case FFI_TYPE_VOID:
      /* Do nothing.  */
      break;
    default:
      abort ();
    }
}
#undef FUNC_NAME

/* Return a Scheme representation of the foreign value at LOC of type
   TYPE.  When RETURN_VALUE_P is true, LOC is assumed to point to a
   return value buffer; otherwise LOC is assumed to point to an
   argument buffer.  */
static SCM
pack (const ffi_type * type, const void *loc, int return_value_p)
{
  switch (type->type)
    {
    case FFI_TYPE_VOID:
      return SCM_UNSPECIFIED;
    case FFI_TYPE_FLOAT:
      return scm_from_double (*(float *) loc);
    case FFI_TYPE_DOUBLE:
      return scm_from_double (*(double *) loc);

      /* For integer return values smaller than `int', libffi stores the
	 result in an `ffi_arg'-long buffer, of which only the
	 significant bits must be kept---hence the pair of casts below.
	 See <http://thread.gmane.org/gmane.comp.lib.ffi.general/406>
	 for details.  */

    case FFI_TYPE_UINT8:
      if (return_value_p)
	return scm_from_uint8 ((scm_t_uint8) *(ffi_arg *) loc);
      else
	return scm_from_uint8 (* (scm_t_uint8 *) loc);
    case FFI_TYPE_SINT8:
      if (return_value_p)
	return scm_from_int8 ((scm_t_int8) *(ffi_arg *) loc);
      else
	return scm_from_int8 (* (scm_t_int8 *) loc);
    case FFI_TYPE_UINT16:
      if (return_value_p)
	return scm_from_uint16 ((scm_t_uint16) *(ffi_arg *) loc);
      else
	return scm_from_uint16 (* (scm_t_uint16 *) loc);
    case FFI_TYPE_SINT16:
      if (return_value_p)
	return scm_from_int16 ((scm_t_int16) *(ffi_arg *) loc);
      else
	return scm_from_int16 (* (scm_t_int16 *) loc);
    case FFI_TYPE_UINT32:
      if (return_value_p)
	return scm_from_uint32 ((scm_t_uint32) *(ffi_arg *) loc);
      else
	return scm_from_uint32 (* (scm_t_uint32 *) loc);
    case FFI_TYPE_SINT32:
      if (return_value_p)
	return scm_from_int32 ((scm_t_int32) *(ffi_arg *) loc);
      else
	return scm_from_int32 (* (scm_t_int32 *) loc);
    case FFI_TYPE_UINT64:
      return scm_from_uint64 (*(scm_t_uint64 *) loc);
    case FFI_TYPE_SINT64:
      return scm_from_int64 (*(scm_t_int64 *) loc);

    case FFI_TYPE_STRUCT:
      {
	void *mem = scm_gc_malloc_pointerless (type->size, "foreign");
	memcpy (mem, loc, type->size);
	return scm_from_pointer (mem, NULL);
      }
    case FFI_TYPE_POINTER:
      return scm_from_pointer (*(void **) loc, NULL);
    default:
      abort ();
    }
}


SCM
scm_i_foreign_call (SCM foreign, const union scm_vm_stack_element *argv)
{
  /* FOREIGN is the pair that cif_to_procedure set as the 0th element of the
     objtable. */
  ffi_cif *cif;
  void (*func) (void);
  scm_t_uint8 *data;
  void *rvalue;
  void **args;
  unsigned i;
  size_t arg_size;
  scm_t_ptrdiff off;

  cif = SCM_POINTER_VALUE (SCM_CAR (foreign));
  func = SCM_POINTER_VALUE (SCM_CDR (foreign));

  /* Argument pointers.  */
  args = alloca (sizeof (void *) * cif->nargs);

  /* Compute the worst-case amount of memory needed to store all the argument
     values.  Note: as of libffi 3.0.9 `cif->bytes' is undocumented and is zero,
     so it can't be used for that purpose.  */
  for (i = 0, arg_size = 0; i < cif->nargs; i++)
    arg_size += cif->arg_types[i]->size + cif->arg_types[i]->alignment - 1;

  /* Space for argument values, followed by return value.  */
  data = alloca (arg_size + cif->rtype->size
		 + max (sizeof (void *), cif->rtype->alignment));

  /* Unpack ARGV to native values, setting ARGV pointers.  */
  for (i = 0, off = 0;
       i < cif->nargs;
       off = (scm_t_uint8 *) args[i] - data + cif->arg_types[i]->size,
	 i++)
    {
      /* Suitably align the storage area for argument I.  */
      args[i] = (void *) ROUND_UP ((scm_t_uintptr) data + off,
				   cif->arg_types[i]->alignment);
      assert ((scm_t_uintptr) args[i] % cif->arg_types[i]->alignment == 0);
      unpack (cif->arg_types[i], args[i], argv[cif->nargs - i - 1].scm, 0);
    }

  /* Prepare space for the return value.  On some platforms, such as
     `armv5tel-*-linux-gnueabi', the return value has to be at least
     word-aligned, even if its type doesn't have any alignment requirement as is
     the case with `char'.  */
  rvalue = (void *) ROUND_UP ((scm_t_uintptr) data + off,
			      max (sizeof (void *), cif->rtype->alignment));

  /* off we go! */
  ffi_call (cif, func, rvalue, args);

  return pack (cif->rtype, rvalue, 1);
}


/* Function pointers aka. "callbacks" or "closures".  */

#ifdef FFI_CLOSURES

/* Trampoline to invoke a libffi closure that wraps a Scheme
   procedure.  */
static void
invoke_closure (ffi_cif *cif, void *ret, void **args, void *data)
{
  size_t i;
  SCM proc, *argv, result;

  proc = SCM_PACK_POINTER (data);

  argv = alloca (cif->nargs * sizeof (*argv));

  /* Pack ARGS to SCM values, setting ARGV pointers.  */
  for (i = 0; i < cif->nargs; i++)
    argv[i] = pack (cif->arg_types[i], args[i], 0);

  result = scm_call_n (proc, argv, cif->nargs);

  unpack (cif->rtype, ret, result, 1);
}

SCM_DEFINE (scm_procedure_to_pointer, "procedure->pointer", 3, 0, 0,
	    (SCM return_type, SCM proc, SCM arg_types),
	    "Return a pointer to a C function of type @var{return_type}\n"
	    "taking arguments of types @var{arg_types} (a list) and\n"
	    "behaving as a proxy to procedure @var{proc}.  Thus\n"
	    "@var{proc}'s arity, supported argument types, and return\n"
	    "type should match @var{return_type} and @var{arg_types}.\n")
#define FUNC_NAME s_scm_procedure_to_pointer
{
  SCM cif_pointer, pointer;
  ffi_cif *cif;
  ffi_status err;
  void *closure, *executable;

  cif = make_cif (return_type, arg_types, FUNC_NAME);

  closure = ffi_closure_alloc (sizeof (ffi_closure), &executable);
  err = ffi_prep_closure_loc ((ffi_closure *) closure, cif,
			      invoke_closure, SCM_UNPACK_POINTER (proc),
			      executable);
  if (err != FFI_OK)
    {
      ffi_closure_free (closure);
      SCM_MISC_ERROR ("`ffi_prep_closure_loc' failed", SCM_EOL);
    }

  /* CIF points to GC-managed memory and it should remain as long as
     POINTER (see below) is live.  Wrap it in a Scheme pointer to then
     hold a weak reference on it.  */
  cif_pointer = scm_from_pointer (cif, NULL);

  if (closure == executable)
    {
      pointer = scm_from_pointer (executable, ffi_closure_free);
      register_weak_reference (pointer,
			       scm_list_2 (proc, cif_pointer));
    }
  else
    {
      /* CLOSURE needs to be freed eventually.  However, since
	 `GC_all_interior_pointers' is disabled, we can't just register
	 a finalizer for CLOSURE.  Instead, we create a pointer object
	 for CLOSURE, with a finalizer, and register it as a weak
	 reference of POINTER.  */
      SCM friend;

      pointer = scm_from_pointer (executable, NULL);
      friend = scm_from_pointer (closure, ffi_closure_free);

      register_weak_reference (pointer,
			       scm_list_3 (proc, cif_pointer, friend));
    }

  return pointer;
}
#undef FUNC_NAME

#endif /* FFI_CLOSURES */



static void
scm_init_foreign (void)
{
#ifndef SCM_MAGIC_SNARFER
#include "libguile/foreign.x"
#endif
  scm_define (sym_void, scm_from_uint8 (SCM_FOREIGN_TYPE_VOID));
  scm_define (sym_float, scm_from_uint8 (SCM_FOREIGN_TYPE_FLOAT));
  scm_define (sym_double, scm_from_uint8 (SCM_FOREIGN_TYPE_DOUBLE));
  scm_define (sym_uint8, scm_from_uint8 (SCM_FOREIGN_TYPE_UINT8));
  scm_define (sym_int8, scm_from_uint8 (SCM_FOREIGN_TYPE_INT8));
  scm_define (sym_uint16, scm_from_uint8 (SCM_FOREIGN_TYPE_UINT16));
  scm_define (sym_int16, scm_from_uint8 (SCM_FOREIGN_TYPE_INT16));
  scm_define (sym_uint32, scm_from_uint8 (SCM_FOREIGN_TYPE_UINT32));
  scm_define (sym_int32, scm_from_uint8 (SCM_FOREIGN_TYPE_INT32));
  scm_define (sym_uint64, scm_from_uint8 (SCM_FOREIGN_TYPE_UINT64));
  scm_define (sym_int64, scm_from_uint8 (SCM_FOREIGN_TYPE_INT64));

  scm_define (sym_short,
#if SIZEOF_SHORT == 8
	      scm_from_uint8 (SCM_FOREIGN_TYPE_INT64)
#elif SIZEOF_SHORT == 4
	      scm_from_uint8 (SCM_FOREIGN_TYPE_INT32)
#elif SIZEOF_SHORT == 2
	      scm_from_uint8 (SCM_FOREIGN_TYPE_INT16)
#else
# error unsupported sizeof (short)
#endif
	      );

  scm_define (sym_unsigned_short,
#if SIZEOF_SHORT == 8
	      scm_from_uint8 (SCM_FOREIGN_TYPE_UINT64)
#elif SIZEOF_SHORT == 4
	      scm_from_uint8 (SCM_FOREIGN_TYPE_UINT32)
#elif SIZEOF_SHORT == 2
	      scm_from_uint8 (SCM_FOREIGN_TYPE_UINT16)
#else
# error unsupported sizeof (short)
#endif
	      );

  scm_define (sym_int,
#if SIZEOF_INT == 8
	      scm_from_uint8 (SCM_FOREIGN_TYPE_INT64)
#elif SIZEOF_INT == 4
	      scm_from_uint8 (SCM_FOREIGN_TYPE_INT32)
#else
# error unsupported sizeof (int)
#endif
	      );

  scm_define (sym_unsigned_int,
#if SIZEOF_UNSIGNED_INT == 8
	      scm_from_uint8 (SCM_FOREIGN_TYPE_UINT64)
#elif SIZEOF_UNSIGNED_INT == 4
	      scm_from_uint8 (SCM_FOREIGN_TYPE_UINT32)
#else
# error unsupported sizeof (unsigned int)
#endif
	      );

  scm_define (sym_long,
#if SIZEOF_LONG == 8
	      scm_from_uint8 (SCM_FOREIGN_TYPE_INT64)
#elif SIZEOF_LONG == 4
	      scm_from_uint8 (SCM_FOREIGN_TYPE_INT32)
#else
# error unsupported sizeof (long)
#endif
	      );

  scm_define (sym_unsigned_long,
#if SIZEOF_UNSIGNED_LONG == 8
	      scm_from_uint8 (SCM_FOREIGN_TYPE_UINT64)
#elif SIZEOF_UNSIGNED_LONG == 4
	      scm_from_uint8 (SCM_FOREIGN_TYPE_UINT32)
#else
# error unsupported sizeof (unsigned long)
#endif
	      );

  scm_define (sym_size_t,
#if SIZEOF_SIZE_T == 8
	      scm_from_uint8 (SCM_FOREIGN_TYPE_UINT64)
#elif SIZEOF_SIZE_T == 4
	      scm_from_uint8 (SCM_FOREIGN_TYPE_UINT32)
#else
# error unsupported sizeof (size_t)
#endif
	      );

  scm_define (sym_ssize_t,
#if SIZEOF_SIZE_T == 8
	      scm_from_uint8 (SCM_FOREIGN_TYPE_INT64)
#elif SIZEOF_SIZE_T == 4
	      scm_from_uint8 (SCM_FOREIGN_TYPE_INT32)
#else
# error unsupported sizeof (ssize_t)
#endif
	      );

  scm_define (sym_ptrdiff_t,
#if SCM_SIZEOF_SCM_T_PTRDIFF == 8
	      scm_from_uint8 (SCM_FOREIGN_TYPE_INT64)
#elif SCM_SIZEOF_SCM_T_PTRDIFF == 4
	      scm_from_uint8 (SCM_FOREIGN_TYPE_INT32)
#else
# error unsupported sizeof (scm_t_ptrdiff)
#endif
	      );

  null_pointer = scm_cell (scm_tc7_pointer, 0);
  scm_define (sym_null, null_pointer);
}

void
scm_register_foreign (void)
{
  scm_c_register_extension ("libguile-" SCM_EFFECTIVE_VERSION,
                            "scm_init_foreign",
                            (scm_t_extension_init_func)scm_init_foreign,
                            NULL);
  pointer_weak_refs = scm_c_make_weak_table (0, SCM_WEAK_TABLE_KIND_KEY);
}

/*
  Local Variables:
  c-file-style: "gnu"
  End:
*/