1//===------------------------ fallback_malloc.ipp -------------------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is dual licensed under the MIT and the University of Illinois Open 6// Source Licenses. See LICENSE.TXT for details. 7// 8// 9// This file implements the "Exception Handling APIs" 10// http://mentorembedded.github.io/cxx-abi/abi-eh.html 11// 12//===----------------------------------------------------------------------===// 13 14#include "config.h" 15 16// A small, simple heap manager based (loosely) on 17// the startup heap manager from FreeBSD, optimized for space. 18// 19// Manages a fixed-size memory pool, supports malloc and free only. 20// No support for realloc. 21// 22// Allocates chunks in multiples of four bytes, with a four byte header 23// for each chunk. The overhead of each chunk is kept low by keeping pointers 24// as two byte offsets within the heap, rather than (4 or 8 byte) pointers. 25 26namespace { 27 28// When POSIX threads are not available, make the mutex operations a nop 29#if LIBCXXABI_HAS_NO_THREADS 30static void * heap_mutex = 0; 31#else 32static pthread_mutex_t heap_mutex = PTHREAD_MUTEX_INITIALIZER; 33#endif 34 35class mutexor { 36public: 37#if LIBCXXABI_HAS_NO_THREADS 38 mutexor ( void * ) {} 39 ~mutexor () {} 40#else 41 mutexor ( pthread_mutex_t *m ) : mtx_(m) { pthread_mutex_lock ( mtx_ ); } 42 ~mutexor () { pthread_mutex_unlock ( mtx_ ); } 43#endif 44private: 45 mutexor ( const mutexor &rhs ); 46 mutexor & operator = ( const mutexor &rhs ); 47#if !LIBCXXABI_HAS_NO_THREADS 48 pthread_mutex_t *mtx_; 49#endif 50 }; 51 52 53#define HEAP_SIZE 512 54char heap [ HEAP_SIZE ]; 55 56typedef unsigned short heap_offset; 57typedef unsigned short heap_size; 58 59struct heap_node { 60 heap_offset next_node; // offset into heap 61 heap_size len; // size in units of "sizeof(heap_node)" 62}; 63 64static const heap_node *list_end = (heap_node *) ( &heap [ HEAP_SIZE ] ); // one past the end of the heap 65static heap_node *freelist = NULL; 66 67heap_node *node_from_offset ( const heap_offset offset ) 68 { return (heap_node *) ( heap + ( offset * sizeof (heap_node))); } 69 70heap_offset offset_from_node ( const heap_node *ptr ) 71 { return static_cast<heap_offset>(static_cast<size_t>(reinterpret_cast<const char *>(ptr) - heap) / sizeof (heap_node)); } 72 73void init_heap () { 74 freelist = (heap_node *) heap; 75 freelist->next_node = offset_from_node ( list_end ); 76 freelist->len = HEAP_SIZE / sizeof (heap_node); 77 } 78 79// How big a chunk we allocate 80size_t alloc_size (size_t len) 81 { return (len + sizeof(heap_node) - 1) / sizeof(heap_node) + 1; } 82 83bool is_fallback_ptr ( void *ptr ) 84 { return ptr >= heap && ptr < ( heap + HEAP_SIZE ); } 85 86void *fallback_malloc(size_t len) { 87 heap_node *p, *prev; 88 const size_t nelems = alloc_size ( len ); 89 mutexor mtx ( &heap_mutex ); 90 91 if ( NULL == freelist ) 92 init_heap (); 93 94// Walk the free list, looking for a "big enough" chunk 95 for (p = freelist, prev = 0; 96 p && p != list_end; prev = p, p = node_from_offset ( p->next_node)) { 97 98 if (p->len > nelems) { // chunk is larger, shorten, and return the tail 99 heap_node *q; 100 101 p->len = static_cast<heap_size>(p->len - nelems); 102 q = p + p->len; 103 q->next_node = 0; 104 q->len = static_cast<heap_size>(nelems); 105 return (void *) (q + 1); 106 } 107 108 if (p->len == nelems) { // exact size match 109 if (prev == 0) 110 freelist = node_from_offset(p->next_node); 111 else 112 prev->next_node = p->next_node; 113 p->next_node = 0; 114 return (void *) (p + 1); 115 } 116 } 117 return NULL; // couldn't find a spot big enough 118} 119 120// Return the start of the next block 121heap_node *after ( struct heap_node *p ) { return p + p->len; } 122 123void fallback_free (void *ptr) { 124 struct heap_node *cp = ((struct heap_node *) ptr) - 1; // retrieve the chunk 125 struct heap_node *p, *prev; 126 127 mutexor mtx ( &heap_mutex ); 128 129#ifdef DEBUG_FALLBACK_MALLOC 130 std::cout << "Freeing item at " << offset_from_node ( cp ) << " of size " << cp->len << std::endl; 131#endif 132 133 for (p = freelist, prev = 0; 134 p && p != list_end; prev = p, p = node_from_offset (p->next_node)) { 135#ifdef DEBUG_FALLBACK_MALLOC 136 std::cout << " p, cp, after (p), after(cp) " 137 << offset_from_node ( p ) << ' ' 138 << offset_from_node ( cp ) << ' ' 139 << offset_from_node ( after ( p )) << ' ' 140 << offset_from_node ( after ( cp )) << std::endl; 141#endif 142 if ( after ( p ) == cp ) { 143#ifdef DEBUG_FALLBACK_MALLOC 144 std::cout << " Appending onto chunk at " << offset_from_node ( p ) << std::endl; 145#endif 146 p->len = static_cast<heap_size>(p->len + cp->len); // make the free heap_node larger 147 return; 148 } 149 else if ( after ( cp ) == p ) { // there's a free heap_node right after 150#ifdef DEBUG_FALLBACK_MALLOC 151 std::cout << " Appending free chunk at " << offset_from_node ( p ) << std::endl; 152#endif 153 cp->len = static_cast<heap_size>(cp->len + p->len); 154 if ( prev == 0 ) { 155 freelist = cp; 156 cp->next_node = p->next_node; 157 } 158 else 159 prev->next_node = offset_from_node(cp); 160 return; 161 } 162 } 163// Nothing to merge with, add it to the start of the free list 164#ifdef DEBUG_FALLBACK_MALLOC 165 std::cout << " Making new free list entry " << offset_from_node ( cp ) << std::endl; 166#endif 167 cp->next_node = offset_from_node ( freelist ); 168 freelist = cp; 169} 170 171#ifdef INSTRUMENT_FALLBACK_MALLOC 172size_t print_free_list () { 173 struct heap_node *p, *prev; 174 heap_size total_free = 0; 175 if ( NULL == freelist ) 176 init_heap (); 177 178 for (p = freelist, prev = 0; 179 p && p != list_end; prev = p, p = node_from_offset (p->next_node)) { 180 std::cout << ( prev == 0 ? "" : " ") << "Offset: " << offset_from_node ( p ) 181 << "\tsize: " << p->len << " Next: " << p->next_node << std::endl; 182 total_free += p->len; 183 } 184 std::cout << "Total Free space: " << total_free << std::endl; 185 return total_free; 186 } 187#endif 188} // end unnamed namespace 189