libstdc++-v3/libsupc++/eh_alloc.cc

   1 // -*- C++ -*- Allocate exception objects.
   2 // Copyright (C) 2001-2016 Free Software Foundation, Inc.
   3 //
   4 // This file is part of GCC.
   5 //
   6 // GCC is free software; you can redistribute it and/or modify
   7 // it under the terms of the GNU General Public License as published by
   8 // the Free Software Foundation; either version 3, or (at your option)
   9 // any later version.
  10 //
  11 // GCC is distributed in the hope that it will be useful,
  12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 // GNU General Public License for more details.
  15 //
  16 // Under Section 7 of GPL version 3, you are granted additional
  17 // permissions described in the GCC Runtime Library Exception, version
  18 // 3.1, as published by the Free Software Foundation.
  19
  20 // You should have received a copy of the GNU General Public License and
  21 // a copy of the GCC Runtime Library Exception along with this program;
  22 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23 // <http://www.gnu.org/licenses/>.
  24
  25 // This is derived from the C++ ABI for IA-64.  Where we diverge
  26 // for cross-architecture compatibility are noted with "@@@".
  27
  28 #include <bits/c++config.h>
  29 #include <cstdlib>
  30 #if _GLIBCXX_HOSTED
  31 #include <cstring>
  32 #endif
  33 #include <climits>
  34 #include <exception>
  35 #include "unwind-cxx.h"
  36 #include <ext/concurrence.h>
  37 #include <new>
  38
  39 #if _GLIBCXX_HOSTED
  40 using std::free;
  41 using std::malloc;
  42 using std::memset;
  43 #else
  44 // In a freestanding environment, these functions may not be available
  45 // -- but for now, we assume that they are.
  46 extern "C" void *malloc (std::size_t);
  47 extern "C" void free(void *);
  48 extern "C" void *memset (void *, int, std::size_t);
  49 #endif
  50
  51 using namespace __cxxabiv1;
  52
  53 // ??? How to control these parameters.
  54
  55 // Guess from the size of basic types how large a buffer is reasonable.
  56 // Note that the basic c++ exception header has 13 pointers and 2 ints,
  57 // so on a system with PSImode pointers we're talking about 56 bytes
  58 // just for overhead.
  59
  60 #if INT_MAX == 32767
  61 # define EMERGENCY_OBJ_SIZE     128
  62 # define EMERGENCY_OBJ_COUNT    16
  63 #elif !defined (_GLIBCXX_LLP64) && LONG_MAX == 2147483647
  64 # define EMERGENCY_OBJ_SIZE     512
  65 # define EMERGENCY_OBJ_COUNT    32
  66 #else
  67 # define EMERGENCY_OBJ_SIZE     1024
  68 # define EMERGENCY_OBJ_COUNT    64
  69 #endif
  70
  71 #ifndef __GTHREADS
  72 # undef EMERGENCY_OBJ_COUNT
  73 # define EMERGENCY_OBJ_COUNT    4
  74 #endif
  75
  76
  77 namespace
  78 {
  79   // A fixed-size heap, variable size object allocator
  80   class pool
  81     {
  82     public:
  83       pool();
  84
  85       void *allocate (std::size_t);
  86       void free (void *);
  87
  88       bool in_pool (void *);
  89
  90     private:
  91       struct free_entry {
  92         std::size_t size;
  93         free_entry *next;
  94       };
  95       struct allocated_entry {
  96         std::size_t size;
  97         char data[] __attribute__((aligned));
  98       };
  99
 100       // A single mutex controlling emergency allocations.
 101       __gnu_cxx::__mutex emergency_mutex;
 102
 103       // The free-list
 104       free_entry *first_free_entry;
 105       // The arena itself - we need to keep track of these only
 106       // to implement in_pool.
 107       char *arena;
 108       std::size_t arena_size;
 109     };
 110
 111   pool::pool()
 112     {
 113       // Allocate the arena - we could add a GLIBCXX_EH_ARENA_SIZE environment
 114       // to make this tunable.
 115       arena_size = (EMERGENCY_OBJ_SIZE * EMERGENCY_OBJ_COUNT
 116                     + EMERGENCY_OBJ_COUNT * sizeof (__cxa_dependent_exception));
 117       arena = (char *)malloc (arena_size);
 118       if (!arena)
 119         {
 120           // If the allocation failed go without an emergency pool.
 121           arena_size = 0;
 122           first_free_entry = NULL;
 123           return;
 124         }
 125
 126       // Populate the free-list with a single entry covering the whole arena
 127       first_free_entry = reinterpret_cast <free_entry *> (arena);
 128       new (first_free_entry) free_entry;
 129       first_free_entry->size = arena_size;
 130       first_free_entry->next = NULL;
 131     }
 132
 133   void *pool::allocate (std::size_t size)
 134     {
 135       __gnu_cxx::__scoped_lock sentry(emergency_mutex);
 136       // We need an additional size_t member plus the padding to
 137       // ensure proper alignment of data.
 138       size += offsetof (allocated_entry, data);
 139       // And we need to at least hand out objects of the size of
 140       // a freelist entry.
 141       if (size < sizeof (free_entry))
 142         size = sizeof (free_entry);
 143       // And we need to align objects we hand out to the maximum
 144       // alignment required on the target (this really aligns the
 145       // tail which will become a new freelist entry).
 146       size = ((size + __alignof__ (allocated_entry::data) - 1)
 147               & ~(__alignof__ (allocated_entry::data) - 1));
 148       // Search for an entry of proper size on the freelist.
 149       free_entry **e;
 150       for (e = &first_free_entry;
 151            *e && (*e)->size < size;
 152            e = &(*e)->next)
 153         ;
 154       if (!*e)
 155         return NULL;
 156       allocated_entry *x;
 157       if ((*e)->size - size >= sizeof (free_entry))
 158         {
 159           // Slit block if it is too large.
 160           free_entry *f = reinterpret_cast <free_entry *>
 161               (reinterpret_cast <char *> (*e) + size);
 162           std::size_t sz = (*e)->size;
 163           free_entry *next = (*e)->next;
 164           new (f) free_entry;
 165           f->next = next;
 166           f->size = sz - size;
 167           x = reinterpret_cast <allocated_entry *> (*e);
 168           new (x) allocated_entry;
 169           x->size = size;
 170           *e = f;
 171         }
 172       else
 173         {
 174           // Exact size match or too small overhead for a free entry.
 175           std::size_t sz = (*e)->size;
 176           free_entry *next = (*e)->next;
 177           x = reinterpret_cast <allocated_entry *> (*e);
 178           new (x) allocated_entry;
 179           x->size = sz;
 180           *e = next;
 181         }
 182       return &x->data;
 183     }
 184
 185   void pool::free (void *data)
 186     {
 187       __gnu_cxx::__scoped_lock sentry(emergency_mutex);
 188       allocated_entry *e = reinterpret_cast <allocated_entry *>
 189         (reinterpret_cast <char *> (data) - offsetof (allocated_entry, data));
 190       std::size_t sz = e->size;
 191       if (!first_free_entry)
 192         {
 193           // If the free list is empty just put the entry there.
 194           free_entry *f = reinterpret_cast <free_entry *> (e);
 195           new (f) free_entry;
 196           f->size = sz;
 197           f->next = NULL;
 198           first_free_entry = f;
 199         }
 200       else if (reinterpret_cast <char *> (e) + sz
 201                == reinterpret_cast <char *> (first_free_entry))
 202         {
 203           // Check if we can merge with the first free entry being right
 204           // after us.
 205           free_entry *f = reinterpret_cast <free_entry *> (e);
 206           new (f) free_entry;
 207           f->size = sz + first_free_entry->size;
 208           f->next = first_free_entry->next;
 209           first_free_entry = f;
 210         }
 211       else
 212         {
 213           // Else search for a free item we can merge with at its end.
 214           free_entry **fe;
 215           for (fe = &first_free_entry;
 216                (*fe)->next
 217                && (reinterpret_cast <char *> ((*fe)->next)
 218                    > reinterpret_cast <char *> (e) + sz);
 219                fe = &(*fe)->next)
 220             ;
 221           if (reinterpret_cast <char *> (*fe) + (*fe)->size
 222               == reinterpret_cast <char *> (e))
 223             /* Merge with the freelist entry.  */
 224             (*fe)->size += sz;
 225           else
 226             {
 227               // Else put it after it which keeps the freelist sorted.
 228               free_entry *f = reinterpret_cast <free_entry *> (e);
 229               new (f) free_entry;
 230               f->size = sz;
 231               f->next = (*fe)->next;
 232               (*fe)->next = f;
 233             }
 234         }
 235     }
 236
 237   bool pool::in_pool (void *ptr)
 238     {
 239       char *p = reinterpret_cast <char *> (ptr);
 240       return (p > arena
 241               && p < arena + arena_size);
 242     }
 243
 244   pool emergency_pool;
 245 }
 246
 247 extern "C" void *
 248 __cxxabiv1::__cxa_allocate_exception(std::size_t thrown_size) _GLIBCXX_NOTHROW
 249 {
 250   void *ret;
 251
 252   thrown_size += sizeof (__cxa_refcounted_exception);
 253   ret = malloc (thrown_size);
 254
 255   if (!ret)
 256     ret = emergency_pool.allocate (thrown_size);
 257
 258   if (!ret)
 259     std::terminate ();
 260
 261   memset (ret, 0, sizeof (__cxa_refcounted_exception));
 262
 263   return (void *)((char *)ret + sizeof (__cxa_refcounted_exception));
 264 }
 265
 266
 267 extern "C" void
 268 __cxxabiv1::__cxa_free_exception(void *vptr) _GLIBCXX_NOTHROW
 269 {
 270   char *ptr = (char *) vptr - sizeof (__cxa_refcounted_exception);
 271   if (emergency_pool.in_pool (ptr))
 272     emergency_pool.free (ptr);
 273   else
 274     free (ptr);
 275 }
 276
 277
 278 extern "C" __cxa_dependent_exception*
 279 __cxxabiv1::__cxa_allocate_dependent_exception() _GLIBCXX_NOTHROW
 280 {
 281   __cxa_dependent_exception *ret;
 282
 283   ret = static_cast<__cxa_dependent_exception*>
 284     (malloc (sizeof (__cxa_dependent_exception)));
 285
 286   if (!ret)
 287     ret = static_cast <__cxa_dependent_exception*>
 288       (emergency_pool.allocate (sizeof (__cxa_dependent_exception)));
 289
 290   if (!ret)
 291     std::terminate ();
 292
 293   memset (ret, 0, sizeof (__cxa_dependent_exception));
 294
 295   return ret;
 296 }
 297
 298
 299 extern "C" void
 300 __cxxabiv1::__cxa_free_dependent_exception
 301   (__cxa_dependent_exception *vptr) _GLIBCXX_NOTHROW
 302 {
 303   if (emergency_pool.in_pool (vptr))
 304     emergency_pool.free (vptr);
 305   else
 306     free (vptr);
 307 }