libiberty/objalloc.c

   1 /* objalloc.c -- routines to allocate memory for objects
   2    Copyright (C) 1997-2021 Free Software Foundation, Inc.
   3    Written by Ian Lance Taylor, Cygnus Solutions.
   4
   5 This program is free software; you can redistribute it and/or modify it
   6 under the terms of the GNU General Public License as published by the
   7 Free Software Foundation; either version 2, or (at your option) any
   8 later version.
   9
  10 This program is distributed in the hope that it will be useful,
  11 but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13 GNU General Public License for more details.
  14
  15 You should have received a copy of the GNU General Public License
  16 along with this program; if not, write to the Free Software
  17 Foundation, 51 Franklin Street - Fifth Floor,
  18 Boston, MA 02110-1301, USA.  */
  19
  20 #include "config.h"
  21 #include "ansidecl.h"
  22
  23 #include "objalloc.h"
  24
  25 /* Get a definition for NULL.  */
  26 #include <stdio.h>
  27
  28 #if VMS
  29 #include <stdlib.h>
  30 #include <unixlib.h>
  31 #else
  32
  33 /* Get a definition for size_t.  */
  34 #include <stddef.h>
  35
  36 #ifdef HAVE_STDLIB_H
  37 #include <stdlib.h>
  38 #else
  39 /* For systems with larger pointers than ints, this must be declared.  */
  40 extern PTR malloc (size_t);
  41 extern void free (PTR);
  42 #endif
  43
  44 #endif
  45
  46 /* These routines allocate space for an object.  Freeing allocated
  47    space may or may not free all more recently allocated space.
  48
  49    We handle large and small allocation requests differently.  If we
  50    don't have enough space in the current block, and the allocation
  51    request is for more than 512 bytes, we simply pass it through to
  52    malloc.  */
  53
  54 /* The objalloc structure is defined in objalloc.h.  */
  55
  56 /* This structure appears at the start of each chunk.  */
  57
  58 struct objalloc_chunk
  59 {
  60   /* Next chunk.  */
  61   struct objalloc_chunk *next;
  62   /* If this chunk contains large objects, this is the value of
  63      current_ptr when this chunk was allocated.  If this chunk
  64      contains small objects, this is NULL.  */
  65   char *current_ptr;
  66 };
  67
  68 /* The aligned size of objalloc_chunk.  */
  69
  70 #define CHUNK_HEADER_SIZE                                       \
  71   ((sizeof (struct objalloc_chunk) + OBJALLOC_ALIGN - 1)        \
  72    &~ (OBJALLOC_ALIGN - 1))
  73
  74 /* We ask for this much memory each time we create a chunk which is to
  75    hold small objects.  */
  76
  77 #define CHUNK_SIZE (4096 - 32)
  78
  79 /* A request for this amount or more is just passed through to malloc.  */
  80
  81 #define BIG_REQUEST (512)
  82
  83 /* Create an objalloc structure.  */
  84
  85 struct objalloc *
  86 objalloc_create (void)
  87 {
  88   struct objalloc *ret;
  89   struct objalloc_chunk *chunk;
  90
  91   ret = (struct objalloc *) malloc (sizeof *ret);
  92   if (ret == NULL)
  93     return NULL;
  94
  95   ret->chunks = (PTR) malloc (CHUNK_SIZE);
  96   if (ret->chunks == NULL)
  97     {
  98       free (ret);
  99       return NULL;
 100     }
 101
 102   chunk = (struct objalloc_chunk *) ret->chunks;
 103   chunk->next = NULL;
 104   chunk->current_ptr = NULL;
 105
 106   ret->current_ptr = (char *) chunk + CHUNK_HEADER_SIZE;
 107   ret->current_space = CHUNK_SIZE - CHUNK_HEADER_SIZE;
 108
 109   return ret;
 110 }
 111
 112 /* Allocate space from an objalloc structure.  */
 113
 114 PTR
 115 _objalloc_alloc (struct objalloc *o, unsigned long original_len)
 116 {
 117   unsigned long len = original_len;
 118
 119   /* We avoid confusion from zero sized objects by always allocating
 120      at least 1 byte.  */
 121   if (len == 0)
 122     len = 1;
 123
 124   len = (len + OBJALLOC_ALIGN - 1) &~ (OBJALLOC_ALIGN - 1);
 125
 126   /* Check for overflow in the alignment operation above and the
 127      malloc argument below. */
 128   if (len + CHUNK_HEADER_SIZE < original_len)
 129     return NULL;
 130
 131   if (len <= o->current_space)
 132     {
 133       o->current_ptr += len;
 134       o->current_space -= len;
 135       return (PTR) (o->current_ptr - len);
 136     }
 137
 138   if (len >= BIG_REQUEST)
 139     {
 140       char *ret;
 141       struct objalloc_chunk *chunk;
 142
 143       ret = (char *) malloc (CHUNK_HEADER_SIZE + len);
 144       if (ret == NULL)
 145         return NULL;
 146
 147       chunk = (struct objalloc_chunk *) ret;
 148       chunk->next = (struct objalloc_chunk *) o->chunks;
 149       chunk->current_ptr = o->current_ptr;
 150
 151       o->chunks = (PTR) chunk;
 152
 153       return (PTR) (ret + CHUNK_HEADER_SIZE);
 154     }
 155   else
 156     {
 157       struct objalloc_chunk *chunk;
 158
 159       chunk = (struct objalloc_chunk *) malloc (CHUNK_SIZE);
 160       if (chunk == NULL)
 161         return NULL;
 162       chunk->next = (struct objalloc_chunk *) o->chunks;
 163       chunk->current_ptr = NULL;
 164
 165       o->current_ptr = (char *) chunk + CHUNK_HEADER_SIZE;
 166       o->current_space = CHUNK_SIZE - CHUNK_HEADER_SIZE;
 167
 168       o->chunks = (PTR) chunk;
 169
 170       return objalloc_alloc (o, len);
 171     }
 172 }
 173
 174 /* Free an entire objalloc structure.  */
 175
 176 void
 177 objalloc_free (struct objalloc *o)
 178 {
 179   struct objalloc_chunk *l;
 180
 181   l = (struct objalloc_chunk *) o->chunks;
 182   while (l != NULL)
 183     {
 184       struct objalloc_chunk *next;
 185
 186       next = l->next;
 187       free (l);
 188       l = next;
 189     }
 190
 191   free (o);
 192 }
 193
 194 /* Free a block from an objalloc structure.  This also frees all more
 195    recently allocated blocks.  */
 196
 197 void
 198 objalloc_free_block (struct objalloc *o, PTR block)
 199 {
 200   struct objalloc_chunk *p, *small;
 201   char *b = (char *) block;
 202
 203   /* First set P to the chunk which contains the block we are freeing,
 204      and set Q to the last small object chunk we see before P.  */
 205   small = NULL;
 206   for (p = (struct objalloc_chunk *) o->chunks; p != NULL; p = p->next)
 207     {
 208       if (p->current_ptr == NULL)
 209         {
 210           if (b > (char *) p && b < (char *) p + CHUNK_SIZE)
 211             break;
 212           small = p;
 213         }
 214       else
 215         {
 216           if (b == (char *) p + CHUNK_HEADER_SIZE)
 217             break;
 218         }
 219     }
 220
 221   /* If we can't find the chunk, the caller has made a mistake.  */
 222   if (p == NULL)
 223     abort ();
 224
 225   if (p->current_ptr == NULL)
 226     {
 227       struct objalloc_chunk *q;
 228       struct objalloc_chunk *first;
 229
 230       /* The block is in a chunk containing small objects.  We can
 231          free every chunk through SMALL, because they have certainly
 232          been allocated more recently.  After SMALL, we will not see
 233          any chunks containing small objects; we can free any big
 234          chunk if the current_ptr is greater than or equal to B.  We
 235          can then reset the new current_ptr to B.  */
 236
 237       first = NULL;
 238       q = (struct objalloc_chunk *) o->chunks;
 239       while (q != p)
 240         {
 241           struct objalloc_chunk *next;
 242
 243           next = q->next;
 244           if (small != NULL)
 245             {
 246               if (small == q)
 247                 small = NULL;
 248               free (q);
 249             }
 250           else if (q->current_ptr > b)
 251             free (q);
 252           else if (first == NULL)
 253             first = q;
 254
 255           q = next;
 256         }
 257
 258       if (first == NULL)
 259         first = p;
 260       o->chunks = (PTR) first;
 261
 262       /* Now start allocating from this small block again.  */
 263       o->current_ptr = b;
 264       o->current_space = ((char *) p + CHUNK_SIZE) - b;
 265     }
 266   else
 267     {
 268       struct objalloc_chunk *q;
 269       char *current_ptr;
 270
 271       /* This block is in a large chunk by itself.  We can free
 272          everything on the list up to and including this block.  We
 273          then start allocating from the next chunk containing small
 274          objects, setting current_ptr from the value stored with the
 275          large chunk we are freeing.  */
 276
 277       current_ptr = p->current_ptr;
 278       p = p->next;
 279
 280       q = (struct objalloc_chunk *) o->chunks;
 281       while (q != p)
 282         {
 283           struct objalloc_chunk *next;
 284
 285           next = q->next;
 286           free (q);
 287           q = next;
 288         }
 289
 290       o->chunks = (PTR) p;
 291
 292       while (p->current_ptr != NULL)
 293         p = p->next;
 294
 295       o->current_ptr = current_ptr;
 296       o->current_space = ((char *) p + CHUNK_SIZE) - current_ptr;
 297     }
 298 }