libobjc/gc.c

/* Basic data types for Objective C.
   Copyright (C) 1998-2025 Free Software Foundation, Inc.
   Contributed by Ovidiu Predescu.

This file is part of GCC.

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

GCC 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 General Public License for more details.

Under Section 7 of GPL version 3, you are granted additional
permissions described in the GCC Runtime Library Exception, version
3.1, as published by the Free Software Foundation.

You should have received a copy of the GNU General Public License and
a copy of the GCC Runtime Library Exception along with this program;
see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
<http://www.gnu.org/licenses/>.  */

#include "objc-private/common.h"
#include "objc/objc.h"

#if OBJC_WITH_GC

#include "tconfig.h"
#include <assert.h>
#include <ctype.h> /* For isdigit.  */
#include <string.h>
#include <stdlib.h>
#include "objc/runtime.h"
#include "objc-private/module-abi-8.h"

#include <gc/gc.h>
#include <limits.h>

/* gc_typed.h uses the following but doesn't declare them */
typedef GC_word word;
typedef GC_signed_word signed_word;
#define BITS_PER_WORD (CHAR_BIT * sizeof (word))

#include <gc/gc_typed.h>

/* The following functions set up in `mask` the corresponding pointers.
   The offset is incremented with the size of the type.  */

#define ROUND(V, A) \
  ({ typeof (V) __v = (V); typeof (A) __a = (A); \
     __a * ((__v+__a - 1)/__a); })

#define SET_BIT_FOR_OFFSET(mask, offset) \
  GC_set_bit (mask, offset / sizeof (void *))

/* Some prototypes */
static void
__objc_gc_setup_struct (GC_bitmap mask, const char *type, int offset);
static void
__objc_gc_setup_union (GC_bitmap mask, const char *type, int offset);


static void
__objc_gc_setup_array (GC_bitmap mask, const char *type, int offset)
{
  int i, len = atoi (type + 1);

  while (isdigit (*++type))
    /* do nothing */;		/* skip the size of the array */

  switch (*type) {
  case _C_ARY_B:
    for (i = 0; i < len; i++)
      __objc_gc_setup_array (mask, type, offset);
    break;

  case _C_STRUCT_B:
    for (i = 0; i < len; i++)
      __objc_gc_setup_struct (mask, type, offset);
    break;

  case _C_UNION_B:
    for (i = 0; i < len; i++)
      __objc_gc_setup_union (mask, type, offset);
    break;

  default:
    break;
  }
}

static void
__objc_gc_setup_struct (GC_bitmap mask, const char *type, int offset)
{
  struct objc_struct_layout layout;
  unsigned int position;
  const char *mtype;

  objc_layout_structure (type, &layout);

  while (objc_layout_structure_next_member (&layout))
    {
      BOOL gc_invisible = NO;

      objc_layout_structure_get_info (&layout, &position, NULL, &mtype);

      /* Skip the variable name */
      if (*mtype == '"')
	{
	  for (mtype++; *mtype++ != '"';)
	    /* do nothing */;
	}

      if (*mtype == _C_GCINVISIBLE)
	{
	  gc_invisible = YES;
	  mtype++;
	}

      /* Add to position the offset of this structure */
      position += offset;

      switch (*mtype) {
      case _C_ID:
      case _C_CLASS:
      case _C_SEL:
      case _C_PTR:
      case _C_CHARPTR:
      case _C_ATOM:
	if (! gc_invisible)
	  SET_BIT_FOR_OFFSET (mask, position);
	break;

      case _C_ARY_B:
	__objc_gc_setup_array (mask, mtype, position);
	break;

      case _C_STRUCT_B:
	__objc_gc_setup_struct (mask, mtype, position);
	break;

      case _C_UNION_B:
	__objc_gc_setup_union (mask, mtype, position);
	break;

      default:
        break;
      }
    }
}

static void
__objc_gc_setup_union (GC_bitmap mask, const char *type, int offset)
{
  /* Sub-optimal, quick implementation: assume the union is made of
     pointers, set up the mask accordingly. */

  int i, size, align;

  /* Skip the variable name */
  if (*type == '"')
    {
      for (type++; *type++ != '"';)
	/* do nothing */;
    }

  size = objc_sizeof_type (type);
  align = objc_alignof_type (type);

  offset = ROUND (offset, align);
  for (i = 0; i < size; i += sizeof (void *))
    {
      SET_BIT_FOR_OFFSET (mask, offset);
      offset += sizeof (void *);
    }
}


/* Iterates over the types in the structure that represents the class
   encoding and sets the bits in mask according to each ivar type.  */
static void
__objc_gc_type_description_from_type (GC_bitmap mask, const char *type)
{
  struct objc_struct_layout layout;
  unsigned int offset, align;
  const char *ivar_type;

  objc_layout_structure (type, &layout);

  while (objc_layout_structure_next_member (&layout))
    {
      BOOL gc_invisible = NO;

      objc_layout_structure_get_info (&layout, &offset, &align, &ivar_type);

      /* Skip the variable name */
      if (*ivar_type == '"')
	{
	  for (ivar_type++; *ivar_type++ != '"';)
	    /* do nothing */;
	}

      if (*ivar_type == _C_GCINVISIBLE)
	{
	  gc_invisible = YES;
	  ivar_type++;
	}

      switch (*ivar_type) {
      case _C_ID:
      case _C_CLASS:
      case _C_SEL:
      case _C_PTR:
      case _C_CHARPTR:
        if (! gc_invisible)
          SET_BIT_FOR_OFFSET (mask, offset);
	break;

      case _C_ARY_B:
	__objc_gc_setup_array (mask, ivar_type, offset);
	break;

      case _C_STRUCT_B:
	__objc_gc_setup_struct (mask, ivar_type, offset);
	break;

      case _C_UNION_B:
	__objc_gc_setup_union (mask, ivar_type, offset);
	break;

      default:
        break;
      }
    }
}

/* Computes in *type the full type encoding of this class including
   its super classes. '*size' gives the total number of bytes allocated
   into *type, '*current' the number of bytes used so far by the
   encoding. */
static void
__objc_class_structure_encoding (Class class, char **type, int *size,
                                 int *current)
{
  int i, ivar_count;
  struct objc_ivar_list *ivars;

  if (! class)
    {
      strcat (*type, "{");
      (*current)++;
      return;
    }

  /* Add the type encodings of the super classes */
  __objc_class_structure_encoding (class->super_class, type, size, current);

  ivars = class->ivars;
  if (! ivars)
    return;

  ivar_count = ivars->ivar_count;

  for (i = 0; i < ivar_count; i++)
    {
      struct objc_ivar *ivar = &(ivars->ivar_list[i]);
      const char *ivar_type = ivar->ivar_type;
      int len = strlen (ivar_type);

      if (*current + len + 1 >= *size)
        {
          /* Increase the size of the encoding string so that it
             contains this ivar's type. */
          *size = ROUND (*current + len + 1, 10);
          *type = objc_realloc (*type, *size);
        }
      strcat (*type + *current, ivar_type);
      *current += len;
    }
}


/* Allocates the memory that will hold the type description for class
   and calls the __objc_class_structure_encoding that generates this
   value. */
void
__objc_generate_gc_type_description (Class class)
{
  GC_bitmap mask;
  int bits_no, size;
  int type_size = 10, current;
  char *class_structure_type;

  if (! CLS_ISCLASS (class))
    return;

  /* We have to create a mask in which each bit counts for a pointer member.
     We take into consideration all the non-pointer instance variables and we
     round them up to the alignment. */

  /* The number of bits in the mask is the size of an instance in bytes divided
     by the size of a pointer. */
  bits_no = (ROUND (class_getInstanceSize (class), sizeof (void *))
             / sizeof (void *));
  size = ROUND (bits_no, BITS_PER_WORD) / BITS_PER_WORD;
  mask = objc_atomic_malloc (size * sizeof (int));
  memset (mask, 0, size * sizeof (int));

  class_structure_type = objc_atomic_malloc (type_size);
  *class_structure_type = current = 0;
  __objc_class_structure_encoding (class, &class_structure_type,
                                   &type_size, &current);
  if (current + 1 == type_size)
    class_structure_type = objc_realloc (class_structure_type, ++type_size);
  strcat (class_structure_type + current, "}");
#ifdef DEBUG
  printf ("type description for '%s' is %s\n", class->name, class_structure_type);
#endif
  
  __objc_gc_type_description_from_type (mask, class_structure_type);
  objc_free (class_structure_type);

#ifdef DEBUG
  printf ("  mask for '%s', type '%s' (bits %d, mask size %d) is:",
	  class_structure_type, class->name, bits_no, size);
  {
    int i;
    for (i = 0; i < size; i++)
      printf (" %lx", mask[i]);
  }
  puts ("");
#endif

  class->gc_object_type = (void *) GC_make_descriptor (mask, bits_no);
}


/* Returns YES if type denotes a pointer type, NO otherwise */
static inline BOOL
__objc_ivar_pointer (const char *type)
{
  type = objc_skip_type_qualifiers (type);

  return (*type == _C_ID
          || *type == _C_CLASS
          || *type == _C_SEL
          || *type == _C_PTR
          || *type == _C_CHARPTR
          || *type == _C_ATOM);
}


/* Mark the instance variable whose name is given by ivarname as a
   weak pointer (a pointer hidden to the garbage collector) if
   gc_invisible is true. If gc_invisible is false it unmarks the
   instance variable and makes it a normal pointer, visible to the
   garbage collector.

   This operation only makes sense on instance variables that are
   pointers.  */
void
class_ivar_set_gcinvisible (Class class, const char *ivarname,
                            BOOL gc_invisible)
{
  int i, ivar_count;
  struct objc_ivar_list *ivars;

  if (! class || ! ivarname)
    return;

  ivars = class->ivars;
  if (! ivars)
    return;

  ivar_count = ivars->ivar_count;

  for (i = 0; i < ivar_count; i++)
    {
      struct objc_ivar *ivar = &(ivars->ivar_list[i]);
      const char *type;

      if (! ivar->ivar_name || strcmp (ivar->ivar_name, ivarname))
	continue;

      assert (ivar->ivar_type);
      type = ivar->ivar_type;

      /* Skip the variable name */
      if (*type == '"')
	{
	  for (type++; *type++ != '"';)
	    /* do nothing */;
	}

      if (*type == _C_GCINVISIBLE)
	{
	  char *new_type;
	  size_t len;

	  if (gc_invisible || ! __objc_ivar_pointer (type))
	    return;	/* The type of the variable already matches the
			   requested gc_invisible type */

	  /* The variable is gc_invisible so we make it gc visible.  */
	  new_type = objc_atomic_malloc (strlen(ivar->ivar_type));
	  len = (type - ivar->ivar_type);
	  memcpy (new_type, ivar->ivar_type, len);
	  new_type[len] = 0;
	  strcat (new_type, type + 1);
	  ivar->ivar_type = new_type;
	}
      else
	{
	  char *new_type;
	  size_t len;

	  if (! gc_invisible || ! __objc_ivar_pointer (type))
	    return;	/* The type of the variable already matches the
			   requested gc_invisible type */

	  /* The variable is gc visible so we make it gc_invisible.  */
	  new_type = objc_malloc (strlen(ivar->ivar_type) + 2);

	  /* Copy the variable name.  */
	  len = (type - ivar->ivar_type);
	  memcpy (new_type, ivar->ivar_type, len);
	  /* Add '!'.  */
	  new_type[len++] = _C_GCINVISIBLE;
	  /* Copy the original types.  */
	  strcpy (new_type + len, type);

	  ivar->ivar_type = new_type;
	}

      __objc_generate_gc_type_description (class);
      return;
    }

  /* Search the instance variable in the superclasses */
  class_ivar_set_gcinvisible (class->super_class, ivarname, gc_invisible);
}

#else /* !OBJC_WITH_GC */

void
__objc_generate_gc_type_description (Class class __attribute__ ((__unused__)))
{
}

void class_ivar_set_gcinvisible (Class class __attribute__ ((__unused__)),
				 const char *ivarname __attribute__ ((__unused__)),
				 BOOL gc_invisible __attribute__ ((__unused__)))
{
}

#endif /* OBJC_WITH_GC */