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

   1 // -*- C++ -*- Allocate exception objects.
   2 // Copyright (C) 2001-2021 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 namespace __gnu_cxx
  77 {
  78   void __freeres();
  79 }
  80
  81 namespace
  82 {
  83   // A fixed-size heap, variable size object allocator
  84   class pool
  85     {
  86     public:
  87       pool();
  88
  89       _GLIBCXX_NODISCARD void *allocate (std::size_t);
  90       void free (void *);
  91
  92       bool in_pool (void *);
  93
  94     private:
  95       struct free_entry {
  96         std::size_t size;
  97         free_entry *next;
  98       };
  99       struct allocated_entry {
 100         std::size_t size;
 101         char data[] __attribute__((aligned));
 102       };
 103
 104       // A single mutex controlling emergency allocations.
 105       __gnu_cxx::__mutex emergency_mutex;
 106
 107       // The free-list
 108       free_entry *first_free_entry;
 109       // The arena itself - we need to keep track of these only
 110       // to implement in_pool.
 111       char *arena;
 112       std::size_t arena_size;
 113
 114       friend void __gnu_cxx::__freeres();
 115     };
 116
 117   pool::pool()
 118     {
 119       // Allocate the arena - we could add a GLIBCXX_EH_ARENA_SIZE environment
 120       // to make this tunable.
 121       arena_size = (EMERGENCY_OBJ_SIZE * EMERGENCY_OBJ_COUNT
 122                     + EMERGENCY_OBJ_COUNT * sizeof (__cxa_dependent_exception));
 123       arena = (char *)malloc (arena_size);
 124       if (!arena)
 125         {
 126           // If the allocation failed go without an emergency pool.
 127           arena_size = 0;
 128           first_free_entry = NULL;
 129           return;
 130         }
 131
 132       // Populate the free-list with a single entry covering the whole arena
 133       first_free_entry = reinterpret_cast <free_entry *> (arena);
 134       new (first_free_entry) free_entry;
 135       first_free_entry->size = arena_size;
 136       first_free_entry->next = NULL;
 137     }
 138
 139   void *pool::allocate (std::size_t size)
 140     {
 141       __gnu_cxx::__scoped_lock sentry(emergency_mutex);
 142       // We need an additional size_t member plus the padding to
 143       // ensure proper alignment of data.
 144       size += offsetof (allocated_entry, data);
 145       // And we need to at least hand out objects of the size of
 146       // a freelist entry.
 147       if (size < sizeof (free_entry))
 148         size = sizeof (free_entry);
 149       // And we need to align objects we hand out to the maximum
 150       // alignment required on the target (this really aligns the
 151       // tail which will become a new freelist entry).
 152       size = ((size + __alignof__ (allocated_entry::data) - 1)
 153               & ~(__alignof__ (allocated_entry::data) - 1));
 154       // Search for an entry of proper size on the freelist.
 155       free_entry **e;
 156       for (e = &first_free_entry;
 157            *e && (*e)->size < size;
 158            e = &(*e)->next)
 159         ;
 160       if (!*e)
 161         return NULL;
 162       allocated_entry *x;
 163       if ((*e)->size - size >= sizeof (free_entry))
 164         {
 165           // Split block if it is too large.
 166           free_entry *f = reinterpret_cast <free_entry *>
 167               (reinterpret_cast <char *> (*e) + size);
 168           std::size_t sz = (*e)->size;
 169           free_entry *next = (*e)->next;
 170           new (f) free_entry;
 171           f->next = next;
 172           f->size = sz - size;
 173           x = reinterpret_cast <allocated_entry *> (*e);
 174           new (x) allocated_entry;
 175           x->size = size;
 176           *e = f;
 177         }
 178       else
 179         {
 180           // Exact size match or too small overhead for a free entry.
 181           std::size_t sz = (*e)->size;
 182           free_entry *next = (*e)->next;
 183           x = reinterpret_cast <allocated_entry *> (*e);
 184           new (x) allocated_entry;
 185           x->size = sz;
 186           *e = next;
 187         }
 188       return &x->data;
 189     }
 190
 191   void pool::free (void *data)
 192     {
 193       __gnu_cxx::__scoped_lock sentry(emergency_mutex);
 194       allocated_entry *e = reinterpret_cast <allocated_entry *>
 195         (reinterpret_cast <char *> (data) - offsetof (allocated_entry, data));
 196       std::size_t sz = e->size;
 197       if (!first_free_entry
 198           || (reinterpret_cast <char *> (e) + sz
 199               < reinterpret_cast <char *> (first_free_entry)))
 200         {
 201           // If the free list is empty or the entry is before the
 202           // first element and cannot be merged with it add it as
 203           // the first free entry.
 204           free_entry *f = reinterpret_cast <free_entry *> (e);
 205           new (f) free_entry;
 206           f->size = sz;
 207           f->next = first_free_entry;
 208           first_free_entry = f;
 209         }
 210       else if (reinterpret_cast <char *> (e) + sz
 211                == reinterpret_cast <char *> (first_free_entry))
 212         {
 213           // Check if we can merge with the first free entry being right
 214           // after us.
 215           free_entry *f = reinterpret_cast <free_entry *> (e);
 216           new (f) free_entry;
 217           f->size = sz + first_free_entry->size;
 218           f->next = first_free_entry->next;
 219           first_free_entry = f;
 220         }
 221       else
 222         {
 223           // Else search for a free item we can merge with at its end.
 224           free_entry **fe;
 225           for (fe = &first_free_entry;
 226                (*fe)->next
 227                && (reinterpret_cast <char *> ((*fe)->next)
 228                    > reinterpret_cast <char *> (e) + sz);
 229                fe = &(*fe)->next)
 230             ;
 231           // If we can merge the next block into us do so and continue
 232           // with the cases below.
 233           if (reinterpret_cast <char *> (e) + sz
 234               == reinterpret_cast <char *> ((*fe)->next))
 235             {
 236               sz += (*fe)->next->size;
 237               (*fe)->next = (*fe)->next->next;
 238             }
 239           if (reinterpret_cast <char *> (*fe) + (*fe)->size
 240               == reinterpret_cast <char *> (e))
 241             // Merge with the freelist entry.
 242             (*fe)->size += sz;
 243           else
 244             {
 245               // Else put it after it which keeps the freelist sorted.
 246               free_entry *f = reinterpret_cast <free_entry *> (e);
 247               new (f) free_entry;
 248               f->size = sz;
 249               f->next = (*fe)->next;
 250               (*fe)->next = f;
 251             }
 252         }
 253     }
 254
 255   bool pool::in_pool (void *ptr)
 256     {
 257       char *p = reinterpret_cast <char *> (ptr);
 258       return (p > arena
 259               && p < arena + arena_size);
 260     }
 261
 262   pool emergency_pool;
 263 }
 264
 265 namespace __gnu_cxx
 266 {
 267   void
 268   __freeres()
 269   {
 270     if (emergency_pool.arena)
 271       {
 272         ::free(emergency_pool.arena);
 273         emergency_pool.arena = 0;
 274       }
 275   }
 276 }
 277
 278 extern "C" void *
 279 __cxxabiv1::__cxa_allocate_exception(std::size_t thrown_size) _GLIBCXX_NOTHROW
 280 {
 281   void *ret;
 282
 283   thrown_size += sizeof (__cxa_refcounted_exception);
 284   ret = malloc (thrown_size);
 285
 286   if (!ret)
 287     ret = emergency_pool.allocate (thrown_size);
 288
 289   if (!ret)
 290     std::terminate ();
 291
 292   memset (ret, 0, sizeof (__cxa_refcounted_exception));
 293
 294   return (void *)((char *)ret + sizeof (__cxa_refcounted_exception));
 295 }
 296
 297
 298 extern "C" void
 299 __cxxabiv1::__cxa_free_exception(void *vptr) _GLIBCXX_NOTHROW
 300 {
 301   char *ptr = (char *) vptr - sizeof (__cxa_refcounted_exception);
 302   if (emergency_pool.in_pool (ptr))
 303     emergency_pool.free (ptr);
 304   else
 305     free (ptr);
 306 }
 307
 308
 309 extern "C" __cxa_dependent_exception*
 310 __cxxabiv1::__cxa_allocate_dependent_exception() _GLIBCXX_NOTHROW
 311 {
 312   __cxa_dependent_exception *ret;
 313
 314   ret = static_cast<__cxa_dependent_exception*>
 315     (malloc (sizeof (__cxa_dependent_exception)));
 316
 317   if (!ret)
 318     ret = static_cast <__cxa_dependent_exception*>
 319       (emergency_pool.allocate (sizeof (__cxa_dependent_exception)));
 320
 321   if (!ret)
 322     std::terminate ();
 323
 324   memset (ret, 0, sizeof (__cxa_dependent_exception));
 325
 326   return ret;
 327 }
 328
 329
 330 extern "C" void
 331 __cxxabiv1::__cxa_free_dependent_exception
 332   (__cxa_dependent_exception *vptr) _GLIBCXX_NOTHROW
 333 {
 334   if (emergency_pool.in_pool (vptr))
 335     emergency_pool.free (vptr);
 336   else
 337     free (vptr);
 338 }