text: // -*- C++ -*- Allocate exception objects.
  // Copyright (C) 2001-2020 Free Software Foundation, Inc.
  //
  // This file is part of GCC.
  //
  // GCC is free software; you can redistribute it and/or modify
  // it under the terms of the GNU General Public License as published by
  // the Free Software Foundation; either version 3, or (at your option)
  // any later version.
  //
  // GCC is distributed in the hope that it will be useful,
  // but WITHOUT ANY WARRANTY; without even the implied warranty of
  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  // GNU General Public License for more details.
  //
  // Under Section 7 of GPL version 3, you are granted additional
  // permissions described in the GCC Runtime Library Exception, version
  // 3.1, as published by the Free Software Foundation.
  
  // You should have received a copy of the GNU General Public License and
  // a copy of the GCC Runtime Library Exception along with this program;
  // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  // <http://www.gnu.org/licenses/>.
  
  // This is derived from the C++ ABI for IA-64.  Where we diverge
  // for cross-architecture compatibility are noted with "@@@".
  
  #include <bits/c++config.h>
  #include <cstdlib>
  #if _GLIBCXX_HOSTED
  #include <cstring>
  #endif
  #include <climits>
  #include <exception>
  #include "unwind-cxx.h"
  #include <ext/concurrence.h>
  #include <new>
  
  #if _GLIBCXX_HOSTED
  using std::free;
  using std::malloc;
  using std::memset;
  #else
  // In a freestanding environment, these functions may not be available
  // -- but for now, we assume that they are.
  extern "C" void *malloc (std::size_t);
  extern "C" void free(void *);
  extern "C" void *memset (void *, int, std::size_t);
  #endif
  
  using namespace __cxxabiv1;
  
  // ??? How to control these parameters.
  
  // Guess from the size of basic types how large a buffer is reasonable.
  // Note that the basic c++ exception header has 13 pointers and 2 ints,
  // so on a system with PSImode pointers we're talking about 56 bytes
  // just for overhead.
  
  #if INT_MAX == 32767
  # define EMERGENCY_OBJ_SIZE	128
  # define EMERGENCY_OBJ_COUNT	16
  #elif !defined (_GLIBCXX_LLP64) && LONG_MAX == 2147483647
  # define EMERGENCY_OBJ_SIZE	512
  # define EMERGENCY_OBJ_COUNT	32
  #else
  # define EMERGENCY_OBJ_SIZE	1024
  # define EMERGENCY_OBJ_COUNT	64
  #endif
  
  #ifndef __GTHREADS
  # undef EMERGENCY_OBJ_COUNT
  # define EMERGENCY_OBJ_COUNT	4
  #endif
  
  namespace __gnu_cxx
  {
    void __freeres();
  }
  
  namespace
  {
    // A fixed-size heap, variable size object allocator
    class pool
      {
      public:
        pool();
  
        _GLIBCXX_NODISCARD void *allocate (std::size_t);
        void free (void *);
  
        bool in_pool (void *);
  
      private:
        struct free_entry {
  	std::size_t size;
  	free_entry *next;
        };
        struct allocated_entry {
  	std::size_t size;
  	char data[] __attribute__((aligned));
        };
  
        // A single mutex controlling emergency allocations.
        __gnu_cxx::__mutex emergency_mutex;
  
        // The free-list
        free_entry *first_free_entry;
        // The arena itself - we need to keep track of these only
        // to implement in_pool.
        char *arena;
        std::size_t arena_size;
  
        friend void __gnu_cxx::__freeres();
      };
  
    pool::pool()
      {
        // Allocate the arena - we could add a GLIBCXX_EH_ARENA_SIZE environment
        // to make this tunable.
        arena_size = (EMERGENCY_OBJ_SIZE * EMERGENCY_OBJ_COUNT
  		    + EMERGENCY_OBJ_COUNT * sizeof (__cxa_dependent_exception));
        arena = (char *)malloc (arena_size);
        if (!arena)
  	{
  	  // If the allocation failed go without an emergency pool.
  	  arena_size = 0;
  	  first_free_entry = NULL;
  	  return;
  	}
  
        // Populate the free-list with a single entry covering the whole arena
        first_free_entry = reinterpret_cast <free_entry *> (arena);
        new (first_free_entry) free_entry;
        first_free_entry->size = arena_size;
        first_free_entry->next = NULL;
      }
  
    void *pool::allocate (std::size_t size)
      {
        __gnu_cxx::__scoped_lock sentry(emergency_mutex);
        // We need an additional size_t member plus the padding to
        // ensure proper alignment of data.
        size += offsetof (allocated_entry, data);
        // And we need to at least hand out objects of the size of
        // a freelist entry.
        if (size < sizeof (free_entry))
  	size = sizeof (free_entry);
        // And we need to align objects we hand out to the maximum
        // alignment required on the target (this really aligns the
        // tail which will become a new freelist entry).
        size = ((size + __alignof__ (allocated_entry::data) - 1)
  	      & ~(__alignof__ (allocated_entry::data) - 1));
        // Search for an entry of proper size on the freelist.
        free_entry **e;
        for (e = &first_free_entry;
  	   *e && (*e)->size < size;
  	   e = &(*e)->next)
  	;
        if (!*e)
  	return NULL;
        allocated_entry *x;
        if ((*e)->size - size >= sizeof (free_entry))
  	{
  	  // Split block if it is too large.
  	  free_entry *f = reinterpret_cast <free_entry *>
  	      (reinterpret_cast <char *> (*e) + size);
  	  std::size_t sz = (*e)->size;
  	  free_entry *next = (*e)->next;
  	  new (f) free_entry;
  	  f->next = next;
  	  f->size = sz - size;
  	  x = reinterpret_cast <allocated_entry *> (*e);
  	  new (x) allocated_entry;
  	  x->size = size;
  	  *e = f;
  	}
        else
  	{
  	  // Exact size match or too small overhead for a free entry.
  	  std::size_t sz = (*e)->size;
  	  free_entry *next = (*e)->next;
  	  x = reinterpret_cast <allocated_entry *> (*e);
  	  new (x) allocated_entry;
  	  x->size = sz;
  	  *e = next;
  	}
        return &x->data;
      }
  
    void pool::free (void *data)
      {
        __gnu_cxx::__scoped_lock sentry(emergency_mutex);
        allocated_entry *e = reinterpret_cast <allocated_entry *>
  	(reinterpret_cast <char *> (data) - offsetof (allocated_entry, data));
        std::size_t sz = e->size;
        if (!first_free_entry
  	  || (reinterpret_cast <char *> (e) + sz
  	      < reinterpret_cast <char *> (first_free_entry)))
  	{
  	  // If the free list is empty or the entry is before the
  	  // first element and cannot be merged with it add it as
  	  // the first free entry.
  	  free_entry *f = reinterpret_cast <free_entry *> (e);
  	  new (f) free_entry;
  	  f->size = sz;
  	  f->next = first_free_entry;
  	  first_free_entry = f;
  	}
        else if (reinterpret_cast <char *> (e) + sz
  	       == reinterpret_cast <char *> (first_free_entry))
  	{
  	  // Check if we can merge with the first free entry being right
  	  // after us.
  	  free_entry *f = reinterpret_cast <free_entry *> (e);
  	  new (f) free_entry;
  	  f->size = sz + first_free_entry->size;
  	  f->next = first_free_entry->next;
  	  first_free_entry = f;
  	}
        else
  	{
  	  // Else search for a free item we can merge with at its end.
  	  free_entry **fe;
  	  for (fe = &first_free_entry;
  	       (*fe)->next
  	       && (reinterpret_cast <char *> ((*fe)->next)
  		   > reinterpret_cast <char *> (e) + sz);
  	       fe = &(*fe)->next)
  	    ;
  	  // If we can merge the next block into us do so and continue
  	  // with the cases below.
  	  if (reinterpret_cast <char *> (e) + sz
  	      == reinterpret_cast <char *> ((*fe)->next))
  	    {
  	      sz += (*fe)->next->size;
  	      (*fe)->next = (*fe)->next->next;
  	    }
  	  if (reinterpret_cast <char *> (*fe) + (*fe)->size
  	      == reinterpret_cast <char *> (e))
  	    // Merge with the freelist entry.
  	    (*fe)->size += sz;
  	  else
  	    {
  	      // Else put it after it which keeps the freelist sorted.
  	      free_entry *f = reinterpret_cast <free_entry *> (e);
  	      new (f) free_entry;
  	      f->size = sz;
  	      f->next = (*fe)->next;
  	      (*fe)->next = f;
  	    }
  	}
      }
  
    bool pool::in_pool (void *ptr)
      {
        char *p = reinterpret_cast <char *> (ptr);
        return (p > arena
  	      && p < arena + arena_size);
      }
  
    pool emergency_pool;
  }
  
  namespace __gnu_cxx
  {
    void
    __freeres()
    {
      if (emergency_pool.arena)
        {
  	::free(emergency_pool.arena);
  	emergency_pool.arena = 0;
        }
    }
  }
  
  extern "C" void *
  __cxxabiv1::__cxa_allocate_exception(std::size_t thrown_size) _GLIBCXX_NOTHROW
  {
    void *ret;
  
    thrown_size += sizeof (__cxa_refcounted_exception);
    ret = malloc (thrown_size);
  
    if (!ret)
      ret = emergency_pool.allocate (thrown_size);
  
    if (!ret)
      std::terminate ();
  
    memset (ret, 0, sizeof (__cxa_refcounted_exception));
  
    return (void *)((char *)ret + sizeof (__cxa_refcounted_exception));
  }
  
  
  extern "C" void
  __cxxabiv1::__cxa_free_exception(void *vptr) _GLIBCXX_NOTHROW
  {
    char *ptr = (char *) vptr - sizeof (__cxa_refcounted_exception);
    if (emergency_pool.in_pool (ptr))
      emergency_pool.free (ptr);
    else
      free (ptr);
  }
  
  
  extern "C" __cxa_dependent_exception*
  __cxxabiv1::__cxa_allocate_dependent_exception() _GLIBCXX_NOTHROW
  {
    __cxa_dependent_exception *ret;
  
    ret = static_cast<__cxa_dependent_exception*>
      (malloc (sizeof (__cxa_dependent_exception)));
  
    if (!ret)
      ret = static_cast <__cxa_dependent_exception*>
        (emergency_pool.allocate (sizeof (__cxa_dependent_exception)));
  
    if (!ret)
      std::terminate ();
  
    memset (ret, 0, sizeof (__cxa_dependent_exception));
  
    return ret;
  }
  
  
  extern "C" void
  __cxxabiv1::__cxa_free_dependent_exception
    (__cxa_dependent_exception *vptr) _GLIBCXX_NOTHROW
  {
    if (emergency_pool.in_pool (vptr))
      emergency_pool.free (vptr);
    else
      free (vptr);
  }
  