libbacktrace/mmap.c

   1 /* mmap.c -- Memory allocation with mmap.
   2    Copyright (C) 2012-2018 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 #ifndef MAP_FAILED
  54 #define MAP_FAILED ((void *)-1)
  55 #endif
  56
  57 /* A list of free memory blocks.  */
  58
  59 struct backtrace_freelist_struct
  60 {
  61   /* Next on list.  */
  62   struct backtrace_freelist_struct *next;
  63   /* Size of this block, including this structure.  */
  64   size_t size;
  65 };
  66
  67 /* Free memory allocated by backtrace_alloc.  */
  68
  69 static void
  70 backtrace_free_locked (struct backtrace_state *state, void *addr, size_t size)
  71 {
  72   /* Just leak small blocks.  We don't have to be perfect.  Don't put
  73      more than 16 entries on the free list, to avoid wasting time
  74      searching when allocating a block.  If we have more than 16
  75      entries, leak the smallest entry.  */
  76
  77   if (size >= sizeof (struct backtrace_freelist_struct))
  78     {
  79       size_t c;
  80       struct backtrace_freelist_struct **ppsmall;
  81       struct backtrace_freelist_struct **pp;
  82       struct backtrace_freelist_struct *p;
  83
  84       c = 0;
  85       ppsmall = NULL;
  86       for (pp = &state->freelist; *pp != NULL; pp = &(*pp)->next)
  87         {
  88           if (ppsmall == NULL || (*pp)->size < (*ppsmall)->size)
  89             ppsmall = pp;
  90           ++c;
  91         }
  92       if (c >= 16)
  93         {
  94           if (size <= (*ppsmall)->size)
  95             return;
  96           *ppsmall = (*ppsmall)->next;
  97         }
  98
  99       p = (struct backtrace_freelist_struct *) addr;
 100       p->next = state->freelist;
 101       p->size = size;
 102       state->freelist = p;
 103     }
 104 }
 105
 106 /* Allocate memory like malloc.  If ERROR_CALLBACK is NULL, don't
 107    report an error.  */
 108
 109 void *
 110 backtrace_alloc (struct backtrace_state *state,
 111                  size_t size, backtrace_error_callback error_callback,
 112                  void *data)
 113 {
 114   void *ret;
 115   int locked;
 116   struct backtrace_freelist_struct **pp;
 117   size_t pagesize;
 118   size_t asksize;
 119   void *page;
 120
 121   ret = NULL;
 122
 123   /* If we can acquire the lock, then see if there is space on the
 124      free list.  If we can't acquire the lock, drop straight into
 125      using mmap.  __sync_lock_test_and_set returns the old state of
 126      the lock, so we have acquired it if it returns 0.  */
 127
 128   if (!state->threaded)
 129     locked = 1;
 130   else
 131     locked = __sync_lock_test_and_set (&state->lock_alloc, 1) == 0;
 132
 133   if (locked)
 134     {
 135       for (pp = &state->freelist; *pp != NULL; pp = &(*pp)->next)
 136         {
 137           if ((*pp)->size >= size)
 138             {
 139               struct backtrace_freelist_struct *p;
 140
 141               p = *pp;
 142               *pp = p->next;
 143
 144               /* Round for alignment; we assume that no type we care about
 145                  is more than 8 bytes.  */
 146               size = (size + 7) & ~ (size_t) 7;
 147               if (size < p->size)
 148                 backtrace_free_locked (state, (char *) p + size,
 149                                        p->size - size);
 150
 151               ret = (void *) p;
 152
 153               break;
 154             }
 155         }
 156
 157       if (state->threaded)
 158         __sync_lock_release (&state->lock_alloc);
 159     }
 160
 161   if (ret == NULL)
 162     {
 163       /* Allocate a new page.  */
 164
 165       pagesize = getpagesize ();
 166       asksize = (size + pagesize - 1) & ~ (pagesize - 1);
 167       page = mmap (NULL, asksize, PROT_READ | PROT_WRITE,
 168                    MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 169       if (page == MAP_FAILED)
 170         {
 171           if (error_callback)
 172             error_callback (data, "mmap", errno);
 173         }
 174       else
 175         {
 176           size = (size + 7) & ~ (size_t) 7;
 177           if (size < asksize)
 178             backtrace_free (state, (char *) page + size, asksize - size,
 179                             error_callback, data);
 180
 181           ret = page;
 182         }
 183     }
 184
 185   return ret;
 186 }
 187
 188 /* Free memory allocated by backtrace_alloc.  */
 189
 190 void
 191 backtrace_free (struct backtrace_state *state, void *addr, size_t size,
 192                 backtrace_error_callback error_callback ATTRIBUTE_UNUSED,
 193                 void *data ATTRIBUTE_UNUSED)
 194 {
 195   int locked;
 196
 197   /* If we are freeing a large aligned block, just release it back to
 198      the system.  This case arises when growing a vector for a large
 199      binary with lots of debug info.  Calling munmap here may cause us
 200      to call mmap again if there is also a large shared library; we
 201      just live with that.  */
 202   if (size >= 16 * 4096)
 203     {
 204       size_t pagesize;
 205
 206       pagesize = getpagesize ();
 207       if (((uintptr_t) addr & (pagesize - 1)) == 0
 208           && (size & (pagesize - 1)) == 0)
 209         {
 210           /* If munmap fails for some reason, just add the block to
 211              the freelist.  */
 212           if (munmap (addr, size) == 0)
 213             return;
 214         }
 215     }
 216
 217   /* If we can acquire the lock, add the new space to the free list.
 218      If we can't acquire the lock, just leak the memory.
 219      __sync_lock_test_and_set returns the old state of the lock, so we
 220      have acquired it if it returns 0.  */
 221
 222   if (!state->threaded)
 223     locked = 1;
 224   else
 225     locked = __sync_lock_test_and_set (&state->lock_alloc, 1) == 0;
 226
 227   if (locked)
 228     {
 229       backtrace_free_locked (state, addr, size);
 230
 231       if (state->threaded)
 232         __sync_lock_release (&state->lock_alloc);
 233     }
 234 }
 235
 236 /* Grow VEC by SIZE bytes.  */
 237
 238 void *
 239 backtrace_vector_grow (struct backtrace_state *state,size_t size,
 240                        backtrace_error_callback error_callback,
 241                        void *data, struct backtrace_vector *vec)
 242 {
 243   void *ret;
 244
 245   if (size > vec->alc)
 246     {
 247       size_t pagesize;
 248       size_t alc;
 249       void *base;
 250
 251       pagesize = getpagesize ();
 252       alc = vec->size + size;
 253       if (vec->size == 0)
 254         alc = 16 * size;
 255       else if (alc < pagesize)
 256         {
 257           alc *= 2;
 258           if (alc > pagesize)
 259             alc = pagesize;
 260         }
 261       else
 262         {
 263           alc *= 2;
 264           alc = (alc + pagesize - 1) & ~ (pagesize - 1);
 265         }
 266       base = backtrace_alloc (state, alc, error_callback, data);
 267       if (base == NULL)
 268         return NULL;
 269       if (vec->base != NULL)
 270         {
 271           memcpy (base, vec->base, vec->size);
 272           backtrace_free (state, vec->base, vec->size + vec->alc,
 273                           error_callback, data);
 274         }
 275       vec->base = base;
 276       vec->alc = alc - vec->size;
 277     }
 278
 279   ret = (char *) vec->base + vec->size;
 280   vec->size += size;
 281   vec->alc -= size;
 282   return ret;
 283 }
 284
 285 /* Finish the current allocation on VEC.  */
 286
 287 void *
 288 backtrace_vector_finish (
 289   struct backtrace_state *state ATTRIBUTE_UNUSED,
 290   struct backtrace_vector *vec,
 291   backtrace_error_callback error_callback ATTRIBUTE_UNUSED,
 292   void *data ATTRIBUTE_UNUSED)
 293 {
 294   void *ret;
 295
 296   ret = vec->base;
 297   vec->base = (char *) vec->base + vec->size;
 298   vec->size = 0;
 299   return ret;
 300 }
 301
 302 /* Release any extra space allocated for VEC.  */
 303
 304 int
 305 backtrace_vector_release (struct backtrace_state *state,
 306                           struct backtrace_vector *vec,
 307                           backtrace_error_callback error_callback,
 308                           void *data)
 309 {
 310   size_t size;
 311   size_t alc;
 312   size_t aligned;
 313
 314   /* Make sure that the block that we free is aligned on an 8-byte
 315      boundary.  */
 316   size = vec->size;
 317   alc = vec->alc;
 318   aligned = (size + 7) & ~ (size_t) 7;
 319   alc -= aligned - size;
 320
 321   backtrace_free (state, (char *) vec->base + aligned, alc,
 322                   error_callback, data);
 323   vec->alc = 0;
 324   return 1;
 325 }