libobjc/gc.c

   1 /* Basic data types for Objective C.
   2    Copyright (C) 1998-2023 Free Software Foundation, Inc.
   3    Contributed by Ovidiu Predescu.
   4
   5 This file is part of GCC.
   6
   7 GCC is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation; either version 3, or (at your option)
  10 any later version.
  11
  12 GCC is distributed in the hope that it will be useful,
  13 but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 GNU General Public License for more details.
  16
  17 Under Section 7 of GPL version 3, you are granted additional
  18 permissions described in the GCC Runtime Library Exception, version
  19 3.1, as published by the Free Software Foundation.
  20
  21 You should have received a copy of the GNU General Public License and
  22 a copy of the GCC Runtime Library Exception along with this program;
  23 see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  24 <http://www.gnu.org/licenses/>.  */
  25
  26 #include "objc-private/common.h"
  27 #include "objc/objc.h"
  28
  29 #if OBJC_WITH_GC
  30
  31 #include "tconfig.h"
  32 #include <assert.h>
  33 #include <ctype.h> /* For isdigit.  */
  34 #include <string.h>
  35 #include <stdlib.h>
  36 #include "objc/runtime.h"
  37 #include "objc-private/module-abi-8.h"
  38
  39 #include <gc/gc.h>
  40 #include <limits.h>
  41
  42 /* gc_typed.h uses the following but doesn't declare them */
  43 typedef GC_word word;
  44 typedef GC_signed_word signed_word;
  45 #define BITS_PER_WORD (CHAR_BIT * sizeof (word))
  46
  47 #include <gc/gc_typed.h>
  48
  49 /* The following functions set up in `mask` the corresponding pointers.
  50    The offset is incremented with the size of the type.  */
  51
  52 #define ROUND(V, A) \
  53   ({ typeof (V) __v = (V); typeof (A) __a = (A); \
  54      __a * ((__v+__a - 1)/__a); })
  55
  56 #define SET_BIT_FOR_OFFSET(mask, offset) \
  57   GC_set_bit (mask, offset / sizeof (void *))
  58
  59 /* Some prototypes */
  60 static void
  61 __objc_gc_setup_struct (GC_bitmap mask, const char *type, int offset);
  62 static void
  63 __objc_gc_setup_union (GC_bitmap mask, const char *type, int offset);
  64
  65
  66 static void
  67 __objc_gc_setup_array (GC_bitmap mask, const char *type, int offset)
  68 {
  69   int i, len = atoi (type + 1);
  70
  71   while (isdigit (*++type))
  72     /* do nothing */;           /* skip the size of the array */
  73
  74   switch (*type) {
  75   case _C_ARY_B:
  76     for (i = 0; i < len; i++)
  77       __objc_gc_setup_array (mask, type, offset);
  78     break;
  79
  80   case _C_STRUCT_B:
  81     for (i = 0; i < len; i++)
  82       __objc_gc_setup_struct (mask, type, offset);
  83     break;
  84
  85   case _C_UNION_B:
  86     for (i = 0; i < len; i++)
  87       __objc_gc_setup_union (mask, type, offset);
  88     break;
  89
  90   default:
  91     break;
  92   }
  93 }
  94
  95 static void
  96 __objc_gc_setup_struct (GC_bitmap mask, const char *type, int offset)
  97 {
  98   struct objc_struct_layout layout;
  99   unsigned int position;
 100   const char *mtype;
 101
 102   objc_layout_structure (type, &layout);
 103
 104   while (objc_layout_structure_next_member (&layout))
 105     {
 106       BOOL gc_invisible = NO;
 107
 108       objc_layout_structure_get_info (&layout, &position, NULL, &mtype);
 109
 110       /* Skip the variable name */
 111       if (*mtype == '"')
 112         {
 113           for (mtype++; *mtype++ != '"';)
 114             /* do nothing */;
 115         }
 116
 117       if (*mtype == _C_GCINVISIBLE)
 118         {
 119           gc_invisible = YES;
 120           mtype++;
 121         }
 122
 123       /* Add to position the offset of this structure */
 124       position += offset;
 125
 126       switch (*mtype) {
 127       case _C_ID:
 128       case _C_CLASS:
 129       case _C_SEL:
 130       case _C_PTR:
 131       case _C_CHARPTR:
 132       case _C_ATOM:
 133         if (! gc_invisible)
 134           SET_BIT_FOR_OFFSET (mask, position);
 135         break;
 136
 137       case _C_ARY_B:
 138         __objc_gc_setup_array (mask, mtype, position);
 139         break;
 140
 141       case _C_STRUCT_B:
 142         __objc_gc_setup_struct (mask, mtype, position);
 143         break;
 144
 145       case _C_UNION_B:
 146         __objc_gc_setup_union (mask, mtype, position);
 147         break;
 148
 149       default:
 150         break;
 151       }
 152     }
 153 }
 154
 155 static void
 156 __objc_gc_setup_union (GC_bitmap mask, const char *type, int offset)
 157 {
 158   /* Sub-optimal, quick implementation: assume the union is made of
 159      pointers, set up the mask accordingly. */
 160
 161   int i, size, align;
 162
 163   /* Skip the variable name */
 164   if (*type == '"')
 165     {
 166       for (type++; *type++ != '"';)
 167         /* do nothing */;
 168     }
 169
 170   size = objc_sizeof_type (type);
 171   align = objc_alignof_type (type);
 172
 173   offset = ROUND (offset, align);
 174   for (i = 0; i < size; i += sizeof (void *))
 175     {
 176       SET_BIT_FOR_OFFSET (mask, offset);
 177       offset += sizeof (void *);
 178     }
 179 }
 180
 181
 182 /* Iterates over the types in the structure that represents the class
 183    encoding and sets the bits in mask according to each ivar type.  */
 184 static void
 185 __objc_gc_type_description_from_type (GC_bitmap mask, const char *type)
 186 {
 187   struct objc_struct_layout layout;
 188   unsigned int offset, align;
 189   const char *ivar_type;
 190
 191   objc_layout_structure (type, &layout);
 192
 193   while (objc_layout_structure_next_member (&layout))
 194     {
 195       BOOL gc_invisible = NO;
 196
 197       objc_layout_structure_get_info (&layout, &offset, &align, &ivar_type);
 198
 199       /* Skip the variable name */
 200       if (*ivar_type == '"')
 201         {
 202           for (ivar_type++; *ivar_type++ != '"';)
 203             /* do nothing */;
 204         }
 205
 206       if (*ivar_type == _C_GCINVISIBLE)
 207         {
 208           gc_invisible = YES;
 209           ivar_type++;
 210         }
 211
 212       switch (*ivar_type) {
 213       case _C_ID:
 214       case _C_CLASS:
 215       case _C_SEL:
 216       case _C_PTR:
 217       case _C_CHARPTR:
 218         if (! gc_invisible)
 219           SET_BIT_FOR_OFFSET (mask, offset);
 220         break;
 221
 222       case _C_ARY_B:
 223         __objc_gc_setup_array (mask, ivar_type, offset);
 224         break;
 225
 226       case _C_STRUCT_B:
 227         __objc_gc_setup_struct (mask, ivar_type, offset);
 228         break;
 229
 230       case _C_UNION_B:
 231         __objc_gc_setup_union (mask, ivar_type, offset);
 232         break;
 233
 234       default:
 235         break;
 236       }
 237     }
 238 }
 239
 240 /* Computes in *type the full type encoding of this class including
 241    its super classes. '*size' gives the total number of bytes allocated
 242    into *type, '*current' the number of bytes used so far by the
 243    encoding. */
 244 static void
 245 __objc_class_structure_encoding (Class class, char **type, int *size,
 246                                  int *current)
 247 {
 248   int i, ivar_count;
 249   struct objc_ivar_list *ivars;
 250
 251   if (! class)
 252     {
 253       strcat (*type, "{");
 254       (*current)++;
 255       return;
 256     }
 257
 258   /* Add the type encodings of the super classes */
 259   __objc_class_structure_encoding (class->super_class, type, size, current);
 260
 261   ivars = class->ivars;
 262   if (! ivars)
 263     return;
 264
 265   ivar_count = ivars->ivar_count;
 266
 267   for (i = 0; i < ivar_count; i++)
 268     {
 269       struct objc_ivar *ivar = &(ivars->ivar_list[i]);
 270       const char *ivar_type = ivar->ivar_type;
 271       int len = strlen (ivar_type);
 272
 273       if (*current + len + 1 >= *size)
 274         {
 275           /* Increase the size of the encoding string so that it
 276              contains this ivar's type. */
 277           *size = ROUND (*current + len + 1, 10);
 278           *type = objc_realloc (*type, *size);
 279         }
 280       strcat (*type + *current, ivar_type);
 281       *current += len;
 282     }
 283 }
 284
 285
 286 /* Allocates the memory that will hold the type description for class
 287    and calls the __objc_class_structure_encoding that generates this
 288    value. */
 289 void
 290 __objc_generate_gc_type_description (Class class)
 291 {
 292   GC_bitmap mask;
 293   int bits_no, size;
 294   int type_size = 10, current;
 295   char *class_structure_type;
 296
 297   if (! CLS_ISCLASS (class))
 298     return;
 299
 300   /* We have to create a mask in which each bit counts for a pointer member.
 301      We take into consideration all the non-pointer instance variables and we
 302      round them up to the alignment. */
 303
 304   /* The number of bits in the mask is the size of an instance in bytes divided
 305      by the size of a pointer. */
 306   bits_no = (ROUND (class_getInstanceSize (class), sizeof (void *))
 307              / sizeof (void *));
 308   size = ROUND (bits_no, BITS_PER_WORD) / BITS_PER_WORD;
 309   mask = objc_atomic_malloc (size * sizeof (int));
 310   memset (mask, 0, size * sizeof (int));
 311
 312   class_structure_type = objc_atomic_malloc (type_size);
 313   *class_structure_type = current = 0;
 314   __objc_class_structure_encoding (class, &class_structure_type,
 315                                    &type_size, &current);
 316   if (current + 1 == type_size)
 317     class_structure_type = objc_realloc (class_structure_type, ++type_size);
 318   strcat (class_structure_type + current, "}");
 319 #ifdef DEBUG
 320   printf ("type description for '%s' is %s\n", class->name, class_structure_type);
 321 #endif
 322
 323   __objc_gc_type_description_from_type (mask, class_structure_type);
 324   objc_free (class_structure_type);
 325
 326 #ifdef DEBUG
 327   printf ("  mask for '%s', type '%s' (bits %d, mask size %d) is:",
 328           class_structure_type, class->name, bits_no, size);
 329   {
 330     int i;
 331     for (i = 0; i < size; i++)
 332       printf (" %lx", mask[i]);
 333   }
 334   puts ("");
 335 #endif
 336
 337   class->gc_object_type = (void *) GC_make_descriptor (mask, bits_no);
 338 }
 339
 340
 341 /* Returns YES if type denotes a pointer type, NO otherwise */
 342 static inline BOOL
 343 __objc_ivar_pointer (const char *type)
 344 {
 345   type = objc_skip_type_qualifiers (type);
 346
 347   return (*type == _C_ID
 348           || *type == _C_CLASS
 349           || *type == _C_SEL
 350           || *type == _C_PTR
 351           || *type == _C_CHARPTR
 352           || *type == _C_ATOM);
 353 }
 354
 355
 356 /* Mark the instance variable whose name is given by ivarname as a
 357    weak pointer (a pointer hidden to the garbage collector) if
 358    gc_invisible is true. If gc_invisible is false it unmarks the
 359    instance variable and makes it a normal pointer, visible to the
 360    garbage collector.
 361
 362    This operation only makes sense on instance variables that are
 363    pointers.  */
 364 void
 365 class_ivar_set_gcinvisible (Class class, const char *ivarname,
 366                             BOOL gc_invisible)
 367 {
 368   int i, ivar_count;
 369   struct objc_ivar_list *ivars;
 370
 371   if (! class || ! ivarname)
 372     return;
 373
 374   ivars = class->ivars;
 375   if (! ivars)
 376     return;
 377
 378   ivar_count = ivars->ivar_count;
 379
 380   for (i = 0; i < ivar_count; i++)
 381     {
 382       struct objc_ivar *ivar = &(ivars->ivar_list[i]);
 383       const char *type;
 384
 385       if (! ivar->ivar_name || strcmp (ivar->ivar_name, ivarname))
 386         continue;
 387
 388       assert (ivar->ivar_type);
 389       type = ivar->ivar_type;
 390
 391       /* Skip the variable name */
 392       if (*type == '"')
 393         {
 394           for (type++; *type++ != '"';)
 395             /* do nothing */;
 396         }
 397
 398       if (*type == _C_GCINVISIBLE)
 399         {
 400           char *new_type;
 401           size_t len;
 402
 403           if (gc_invisible || ! __objc_ivar_pointer (type))
 404             return;     /* The type of the variable already matches the
 405                            requested gc_invisible type */
 406
 407           /* The variable is gc_invisible so we make it gc visible.  */
 408           new_type = objc_atomic_malloc (strlen(ivar->ivar_type));
 409           len = (type - ivar->ivar_type);
 410           memcpy (new_type, ivar->ivar_type, len);
 411           new_type[len] = 0;
 412           strcat (new_type, type + 1);
 413           ivar->ivar_type = new_type;
 414         }
 415       else
 416         {
 417           char *new_type;
 418           size_t len;
 419
 420           if (! gc_invisible || ! __objc_ivar_pointer (type))
 421             return;     /* The type of the variable already matches the
 422                            requested gc_invisible type */
 423
 424           /* The variable is gc visible so we make it gc_invisible.  */
 425           new_type = objc_malloc (strlen(ivar->ivar_type) + 2);
 426
 427           /* Copy the variable name.  */
 428           len = (type - ivar->ivar_type);
 429           memcpy (new_type, ivar->ivar_type, len);
 430           /* Add '!'.  */
 431           new_type[len++] = _C_GCINVISIBLE;
 432           /* Copy the original types.  */
 433           strcpy (new_type + len, type);
 434
 435           ivar->ivar_type = new_type;
 436         }
 437
 438       __objc_generate_gc_type_description (class);
 439       return;
 440     }
 441
 442   /* Search the instance variable in the superclasses */
 443   class_ivar_set_gcinvisible (class->super_class, ivarname, gc_invisible);
 444 }
 445
 446 #else /* !OBJC_WITH_GC */
 447
 448 void
 449 __objc_generate_gc_type_description (Class class __attribute__ ((__unused__)))
 450 {
 451 }
 452
 453 void class_ivar_set_gcinvisible (Class class __attribute__ ((__unused__)),
 454                                  const char *ivarname __attribute__ ((__unused__)),
 455                                  BOOL gc_invisible __attribute__ ((__unused__)))
 456 {
 457 }
 458
 459 #endif /* OBJC_WITH_GC */