libbacktrace/mmap.c

   1 /* mmap.c -- Memory allocation with mmap.
   2    Copyright (C) 2012-2017 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.  */
  73   if (size >= sizeof (struct backtrace_freelist_struct))
  74     {
  75       struct backtrace_freelist_struct *p;
  76
  77       p = (struct backtrace_freelist_struct *) addr;
  78       p->next = state->freelist;
  79       p->size = size;
  80       state->freelist = p;
  81     }
  82 }
  83
  84 /* Allocate memory like malloc.  If ERROR_CALLBACK is NULL, don't
  85    report an error.  */
  86
  87 void *
  88 backtrace_alloc (struct backtrace_state *state,
  89                  size_t size, backtrace_error_callback error_callback,
  90                  void *data)
  91 {
  92   void *ret;
  93   int locked;
  94   struct backtrace_freelist_struct **pp;
  95   size_t pagesize;
  96   size_t asksize;
  97   void *page;
  98
  99   ret = NULL;
 100
 101   /* If we can acquire the lock, then see if there is space on the
 102      free list.  If we can't acquire the lock, drop straight into
 103      using mmap.  __sync_lock_test_and_set returns the old state of
 104      the lock, so we have acquired it if it returns 0.  */
 105
 106   if (!state->threaded)
 107     locked = 1;
 108   else
 109     locked = __sync_lock_test_and_set (&state->lock_alloc, 1) == 0;
 110
 111   if (locked)
 112     {
 113       for (pp = &state->freelist; *pp != NULL; pp = &(*pp)->next)
 114         {
 115           if ((*pp)->size >= size)
 116             {
 117               struct backtrace_freelist_struct *p;
 118
 119               p = *pp;
 120               *pp = p->next;
 121
 122               /* Round for alignment; we assume that no type we care about
 123                  is more than 8 bytes.  */
 124               size = (size + 7) & ~ (size_t) 7;
 125               if (size < p->size)
 126                 backtrace_free_locked (state, (char *) p + size,
 127                                        p->size - size);
 128
 129               ret = (void *) p;
 130
 131               break;
 132             }
 133         }
 134
 135       if (state->threaded)
 136         __sync_lock_release (&state->lock_alloc);
 137     }
 138
 139   if (ret == NULL)
 140     {
 141       /* Allocate a new page.  */
 142
 143       pagesize = getpagesize ();
 144       asksize = (size + pagesize - 1) & ~ (pagesize - 1);
 145       page = mmap (NULL, asksize, PROT_READ | PROT_WRITE,
 146                    MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 147       if (page == MAP_FAILED)
 148         {
 149           if (error_callback)
 150             error_callback (data, "mmap", errno);
 151         }
 152       else
 153         {
 154           size = (size + 7) & ~ (size_t) 7;
 155           if (size < asksize)
 156             backtrace_free (state, (char *) page + size, asksize - size,
 157                             error_callback, data);
 158
 159           ret = page;
 160         }
 161     }
 162
 163   return ret;
 164 }
 165
 166 /* Free memory allocated by backtrace_alloc.  */
 167
 168 void
 169 backtrace_free (struct backtrace_state *state, void *addr, size_t size,
 170                 backtrace_error_callback error_callback ATTRIBUTE_UNUSED,
 171                 void *data ATTRIBUTE_UNUSED)
 172 {
 173   int locked;
 174
 175   /* If we are freeing a large aligned block, just release it back to
 176      the system.  This case arises when growing a vector for a large
 177      binary with lots of debug info.  Calling munmap here may cause us
 178      to call mmap again if there is also a large shared library; we
 179      just live with that.  */
 180   if (size >= 16 * 4096)
 181     {
 182       size_t pagesize;
 183
 184       pagesize = getpagesize ();
 185       if (((uintptr_t) addr & (pagesize - 1)) == 0
 186           && (size & (pagesize - 1)) == 0)
 187         {
 188           /* If munmap fails for some reason, just add the block to
 189              the freelist.  */
 190           if (munmap (addr, size) == 0)
 191             return;
 192         }
 193     }
 194
 195   /* If we can acquire the lock, add the new space to the free list.
 196      If we can't acquire the lock, just leak the memory.
 197      __sync_lock_test_and_set returns the old state of the lock, so we
 198      have acquired it if it returns 0.  */
 199
 200   if (!state->threaded)
 201     locked = 1;
 202   else
 203     locked = __sync_lock_test_and_set (&state->lock_alloc, 1) == 0;
 204
 205   if (locked)
 206     {
 207       backtrace_free_locked (state, addr, size);
 208
 209       if (state->threaded)
 210         __sync_lock_release (&state->lock_alloc);
 211     }
 212 }
 213
 214 /* Grow VEC by SIZE bytes.  */
 215
 216 void *
 217 backtrace_vector_grow (struct backtrace_state *state,size_t size,
 218                        backtrace_error_callback error_callback,
 219                        void *data, struct backtrace_vector *vec)
 220 {
 221   void *ret;
 222
 223   if (size > vec->alc)
 224     {
 225       size_t pagesize;
 226       size_t alc;
 227       void *base;
 228
 229       pagesize = getpagesize ();
 230       alc = vec->size + size;
 231       if (vec->size == 0)
 232         alc = 16 * size;
 233       else if (alc < pagesize)
 234         {
 235           alc *= 2;
 236           if (alc > pagesize)
 237             alc = pagesize;
 238         }
 239       else
 240         {
 241           alc *= 2;
 242           alc = (alc + pagesize - 1) & ~ (pagesize - 1);
 243         }
 244       base = backtrace_alloc (state, alc, error_callback, data);
 245       if (base == NULL)
 246         return NULL;
 247       if (vec->base != NULL)
 248         {
 249           memcpy (base, vec->base, vec->size);
 250           backtrace_free (state, vec->base, vec->size + vec->alc,
 251                           error_callback, data);
 252         }
 253       vec->base = base;
 254       vec->alc = alc - vec->size;
 255     }
 256
 257   ret = (char *) vec->base + vec->size;
 258   vec->size += size;
 259   vec->alc -= size;
 260   return ret;
 261 }
 262
 263 /* Finish the current allocation on VEC.  */
 264
 265 void *
 266 backtrace_vector_finish (
 267   struct backtrace_state *state ATTRIBUTE_UNUSED,
 268   struct backtrace_vector *vec,
 269   backtrace_error_callback error_callback ATTRIBUTE_UNUSED,
 270   void *data ATTRIBUTE_UNUSED)
 271 {
 272   void *ret;
 273
 274   ret = vec->base;
 275   vec->base = (char *) vec->base + vec->size;
 276   vec->size = 0;
 277   return ret;
 278 }
 279
 280 /* Release any extra space allocated for VEC.  */
 281
 282 int
 283 backtrace_vector_release (struct backtrace_state *state,
 284                           struct backtrace_vector *vec,
 285                           backtrace_error_callback error_callback,
 286                           void *data)
 287 {
 288   size_t size;
 289   size_t alc;
 290   size_t aligned;
 291
 292   /* Make sure that the block that we free is aligned on an 8-byte
 293      boundary.  */
 294   size = vec->size;
 295   alc = vec->alc;
 296   aligned = (size + 7) & ~ (size_t) 7;
 297   alc -= aligned - size;
 298
 299   backtrace_free (state, (char *) vec->base + aligned, alc,
 300                   error_callback, data);
 301   vec->alc = 0;
 302   return 1;
 303 }