libbacktrace/mmap.c

   1 /* mmap.c -- Memory allocation with mmap.
   2    Copyright (C) 2012-2013 Free Software Foundation, Inc.
   3    Written by Ian Lance Taylor, Google.
   4
   5 Redistribution and use in source and binary forms, with or without
   6 modification, are permitted provided that the following conditions are
   7 met:
   8
   9     (1) Redistributions of source code must retain the above copyright
  10     notice, this list of conditions and the following disclaimer.
  11
  12     (2) Redistributions in binary form must reproduce the above copyright
  13     notice, this list of conditions and the following disclaimer in
  14     the documentation and/or other materials provided with the
  15     distribution.
  16
  17     (3) The name of the author may not be used to
  18     endorse or promote products derived from this software without
  19     specific prior written permission.
  20
  21 THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  22 IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  23 WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  24 DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
  25 INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  26 (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  27 SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28 HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
  29 STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
  30 IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  31 POSSIBILITY OF SUCH DAMAGE.  */
  32
  33 #include "config.h"
  34
  35 #include <errno.h>
  36 #include <string.h>
  37 #include <stdlib.h>
  38 #include <unistd.h>
  39 #include <sys/types.h>
  40 #include <sys/mman.h>
  41
  42 #include "backtrace.h"
  43 #include "internal.h"
  44
  45 /* Memory allocation on systems that provide anonymous mmap.  This
  46    permits the backtrace functions to be invoked from a signal
  47    handler, assuming that mmap is async-signal safe.  */
  48
  49 #ifndef MAP_ANONYMOUS
  50 #define MAP_ANONYMOUS MAP_ANON
  51 #endif
  52
  53 /* A list of free memory blocks.  */
  54
  55 struct backtrace_freelist_struct
  56 {
  57   /* Next on list.  */
  58   struct backtrace_freelist_struct *next;
  59   /* Size of this block, including this structure.  */
  60   size_t size;
  61 };
  62
  63 /* Free memory allocated by backtrace_alloc.  */
  64
  65 static void
  66 backtrace_free_locked (struct backtrace_state *state, void *addr, size_t size)
  67 {
  68   /* Just leak small blocks.  We don't have to be perfect.  */
  69   if (size >= sizeof (struct backtrace_freelist_struct))
  70     {
  71       struct backtrace_freelist_struct *p;
  72
  73       p = (struct backtrace_freelist_struct *) addr;
  74       p->next = state->freelist;
  75       p->size = size;
  76       state->freelist = p;
  77     }
  78 }
  79
  80 /* Allocate memory like malloc.  */
  81
  82 void *
  83 backtrace_alloc (struct backtrace_state *state,
  84                  size_t size, backtrace_error_callback error_callback,
  85                  void *data)
  86 {
  87   void *ret;
  88   int locked;
  89   struct backtrace_freelist_struct **pp;
  90   size_t pagesize;
  91   size_t asksize;
  92   void *page;
  93
  94   ret = NULL;
  95
  96   /* If we can acquire the lock, then see if there is space on the
  97      free list.  If we can't acquire the lock, drop straight into
  98      using mmap.  __sync_lock_test_and_set returns the old state of
  99      the lock, so we have acquired it if it returns 0.  */
 100
 101   if (!state->threaded)
 102     locked = 1;
 103   else
 104     locked = __sync_lock_test_and_set (&state->lock_alloc, 1) == 0;
 105
 106   if (locked)
 107     {
 108       for (pp = &state->freelist; *pp != NULL; pp = &(*pp)->next)
 109         {
 110           if ((*pp)->size >= size)
 111             {
 112               struct backtrace_freelist_struct *p;
 113
 114               p = *pp;
 115               *pp = p->next;
 116
 117               /* Round for alignment; we assume that no type we care about
 118                  is more than 8 bytes.  */
 119               size = (size + 7) & ~ (size_t) 7;
 120               if (size < p->size)
 121                 backtrace_free_locked (state, (char *) p + size,
 122                                        p->size - size);
 123
 124               ret = (void *) p;
 125
 126               break;
 127             }
 128         }
 129
 130       if (state->threaded)
 131         __sync_lock_release (&state->lock_alloc);
 132     }
 133
 134   if (ret == NULL)
 135     {
 136       /* Allocate a new page.  */
 137
 138       pagesize = getpagesize ();
 139       asksize = (size + pagesize - 1) & ~ (pagesize - 1);
 140       page = mmap (NULL, asksize, PROT_READ | PROT_WRITE,
 141                    MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 142       if (page == NULL)
 143         error_callback (data, "mmap", errno);
 144       else
 145         {
 146           size = (size + 7) & ~ (size_t) 7;
 147           if (size < asksize)
 148             backtrace_free (state, (char *) page + size, asksize - size,
 149                             error_callback, data);
 150
 151           ret = page;
 152         }
 153     }
 154
 155   return ret;
 156 }
 157
 158 /* Free memory allocated by backtrace_alloc.  */
 159
 160 void
 161 backtrace_free (struct backtrace_state *state, void *addr, size_t size,
 162                 backtrace_error_callback error_callback ATTRIBUTE_UNUSED,
 163                 void *data ATTRIBUTE_UNUSED)
 164 {
 165   int locked;
 166
 167   /* If we can acquire the lock, add the new space to the free list.
 168      If we can't acquire the lock, just leak the memory.
 169      __sync_lock_test_and_set returns the old state of the lock, so we
 170      have acquired it if it returns 0.  */
 171
 172   if (!state->threaded)
 173     locked = 1;
 174   else
 175     locked = __sync_lock_test_and_set (&state->lock_alloc, 1) == 0;
 176
 177   if (locked)
 178     {
 179       backtrace_free_locked (state, addr, size);
 180
 181       if (state->threaded)
 182         __sync_lock_release (&state->lock_alloc);
 183     }
 184 }
 185
 186 /* Grow VEC by SIZE bytes.  */
 187
 188 void *
 189 backtrace_vector_grow (struct backtrace_state *state,size_t size,
 190                        backtrace_error_callback error_callback,
 191                        void *data, struct backtrace_vector *vec)
 192 {
 193   void *ret;
 194
 195   if (size > vec->alc)
 196     {
 197       size_t pagesize;
 198       size_t alc;
 199       void *base;
 200
 201       pagesize = getpagesize ();
 202       alc = vec->size + size;
 203       if (vec->size == 0)
 204         alc = 16 * size;
 205       else if (alc < pagesize)
 206         {
 207           alc *= 2;
 208           if (alc > pagesize)
 209             alc = pagesize;
 210         }
 211       else
 212         alc = (alc + pagesize - 1) & ~ (pagesize - 1);
 213       base = backtrace_alloc (state, alc, error_callback, data);
 214       if (base == NULL)
 215         return NULL;
 216       if (vec->base != NULL)
 217         {
 218           memcpy (base, vec->base, vec->size);
 219           backtrace_free (state, vec->base, vec->alc, error_callback, data);
 220         }
 221       vec->base = base;
 222       vec->alc = alc - vec->size;
 223     }
 224
 225   ret = (char *) vec->base + vec->size;
 226   vec->size += size;
 227   vec->alc -= size;
 228   return ret;
 229 }
 230
 231 /* Finish the current allocation on VEC.  */
 232
 233 void
 234 backtrace_vector_finish (struct backtrace_state *state ATTRIBUTE_UNUSED,
 235                          struct backtrace_vector *vec)
 236 {
 237   vec->base = (char *) vec->base + vec->size;
 238   vec->size = 0;
 239 }
 240
 241 /* Release any extra space allocated for VEC.  */
 242
 243 int
 244 backtrace_vector_release (struct backtrace_state *state,
 245                           struct backtrace_vector *vec,
 246                           backtrace_error_callback error_callback,
 247                           void *data)
 248 {
 249   size_t size;
 250   size_t alc;
 251   size_t aligned;
 252
 253   /* Make sure that the block that we free is aligned on an 8-byte
 254      boundary.  */
 255   size = vec->size;
 256   alc = vec->alc;
 257   aligned = (size + 7) & ~ (size_t) 7;
 258   alc -= aligned - size;
 259
 260   backtrace_free (state, (char *) vec->base + aligned, alc,
 261                   error_callback, data);
 262   vec->alc = 0;
 263   return 1;
 264 }