diff options
author | Igor Kudrin <ikudrin.dev@gmail.com> | 2016-09-29 06:38:06 +0000 |
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committer | Igor Kudrin <ikudrin.dev@gmail.com> | 2016-09-29 06:38:06 +0000 |
commit | feb04d70afb8388150f2ba40df8333ca4c4817ec (patch) | |
tree | 768b51034d36d5bf7d60832406dcbdbc08c74938 /src/fallback_malloc.cpp | |
parent | a0863319144d468d524c8606e56ebbfb77c2bf71 (diff) |
[libc++abi] Use fallback_malloc to allocate __cxa_eh_globals in case of dynamic memory exhaustion.
Throwing an exception for the first time may lead to call calloc to
allocate memory for __cxa_eh_globals. If the memory pool is exhausted
at that moment, it results in abnormal termination of the program.
This patch addresses the issue by using fallback_malloc in that case.
Differential Revision: https://reviews.llvm.org/D17815
git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@282692 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'src/fallback_malloc.cpp')
-rw-r--r-- | src/fallback_malloc.cpp | 226 |
1 files changed, 226 insertions, 0 deletions
diff --git a/src/fallback_malloc.cpp b/src/fallback_malloc.cpp new file mode 100644 index 0000000..a436ed0 --- /dev/null +++ b/src/fallback_malloc.cpp @@ -0,0 +1,226 @@ +//===------------------------ fallback_malloc.cpp -------------------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is dual licensed under the MIT and the University of Illinois Open +// Source Licenses. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// + +#include "fallback_malloc.h" + +#include "config.h" + +#include <cstdlib> // for malloc, calloc, free +#include <cstring> // for memset + +#ifndef _LIBCXXABI_HAS_NO_THREADS +#include <pthread.h> // for mutexes +#endif + +// A small, simple heap manager based (loosely) on +// the startup heap manager from FreeBSD, optimized for space. +// +// Manages a fixed-size memory pool, supports malloc and free only. +// No support for realloc. +// +// Allocates chunks in multiples of four bytes, with a four byte header +// for each chunk. The overhead of each chunk is kept low by keeping pointers +// as two byte offsets within the heap, rather than (4 or 8 byte) pointers. + +namespace { + +// When POSIX threads are not available, make the mutex operations a nop +#ifndef _LIBCXXABI_HAS_NO_THREADS +static pthread_mutex_t heap_mutex = PTHREAD_MUTEX_INITIALIZER; +#else +static void * heap_mutex = 0; +#endif + +class mutexor { +public: +#ifndef _LIBCXXABI_HAS_NO_THREADS + mutexor ( pthread_mutex_t *m ) : mtx_(m) { pthread_mutex_lock ( mtx_ ); } + ~mutexor () { pthread_mutex_unlock ( mtx_ ); } +#else + mutexor ( void * ) {} + ~mutexor () {} +#endif +private: + mutexor ( const mutexor &rhs ); + mutexor & operator = ( const mutexor &rhs ); +#ifndef _LIBCXXABI_HAS_NO_THREADS + pthread_mutex_t *mtx_; +#endif + }; + + +static const size_t HEAP_SIZE = 512; +char heap [ HEAP_SIZE ] __attribute__((aligned)); + +typedef unsigned short heap_offset; +typedef unsigned short heap_size; + +struct heap_node { + heap_offset next_node; // offset into heap + heap_size len; // size in units of "sizeof(heap_node)" +}; + +static const heap_node *list_end = (heap_node *) ( &heap [ HEAP_SIZE ] ); // one past the end of the heap +static heap_node *freelist = NULL; + +heap_node *node_from_offset ( const heap_offset offset ) + { return (heap_node *) ( heap + ( offset * sizeof (heap_node))); } + +heap_offset offset_from_node ( const heap_node *ptr ) + { return static_cast<heap_offset>(static_cast<size_t>(reinterpret_cast<const char *>(ptr) - heap) / sizeof (heap_node)); } + +void init_heap () { + freelist = (heap_node *) heap; + freelist->next_node = offset_from_node ( list_end ); + freelist->len = HEAP_SIZE / sizeof (heap_node); + } + +// How big a chunk we allocate +size_t alloc_size (size_t len) + { return (len + sizeof(heap_node) - 1) / sizeof(heap_node) + 1; } + +bool is_fallback_ptr ( void *ptr ) + { return ptr >= heap && ptr < ( heap + HEAP_SIZE ); } + +void *fallback_malloc(size_t len) { + heap_node *p, *prev; + const size_t nelems = alloc_size ( len ); + mutexor mtx ( &heap_mutex ); + + if ( NULL == freelist ) + init_heap (); + +// Walk the free list, looking for a "big enough" chunk + for (p = freelist, prev = 0; + p && p != list_end; prev = p, p = node_from_offset ( p->next_node)) { + + if (p->len > nelems) { // chunk is larger, shorten, and return the tail + heap_node *q; + + p->len = static_cast<heap_size>(p->len - nelems); + q = p + p->len; + q->next_node = 0; + q->len = static_cast<heap_size>(nelems); + return (void *) (q + 1); + } + + if (p->len == nelems) { // exact size match + if (prev == 0) + freelist = node_from_offset(p->next_node); + else + prev->next_node = p->next_node; + p->next_node = 0; + return (void *) (p + 1); + } + } + return NULL; // couldn't find a spot big enough +} + +// Return the start of the next block +heap_node *after ( struct heap_node *p ) { return p + p->len; } + +void fallback_free (void *ptr) { + struct heap_node *cp = ((struct heap_node *) ptr) - 1; // retrieve the chunk + struct heap_node *p, *prev; + + mutexor mtx ( &heap_mutex ); + +#ifdef DEBUG_FALLBACK_MALLOC + std::cout << "Freeing item at " << offset_from_node ( cp ) << " of size " << cp->len << std::endl; +#endif + + for (p = freelist, prev = 0; + p && p != list_end; prev = p, p = node_from_offset (p->next_node)) { +#ifdef DEBUG_FALLBACK_MALLOC + std::cout << " p, cp, after (p), after(cp) " + << offset_from_node ( p ) << ' ' + << offset_from_node ( cp ) << ' ' + << offset_from_node ( after ( p )) << ' ' + << offset_from_node ( after ( cp )) << std::endl; +#endif + if ( after ( p ) == cp ) { +#ifdef DEBUG_FALLBACK_MALLOC + std::cout << " Appending onto chunk at " << offset_from_node ( p ) << std::endl; +#endif + p->len = static_cast<heap_size>(p->len + cp->len); // make the free heap_node larger + return; + } + else if ( after ( cp ) == p ) { // there's a free heap_node right after +#ifdef DEBUG_FALLBACK_MALLOC + std::cout << " Appending free chunk at " << offset_from_node ( p ) << std::endl; +#endif + cp->len = static_cast<heap_size>(cp->len + p->len); + if ( prev == 0 ) { + freelist = cp; + cp->next_node = p->next_node; + } + else + prev->next_node = offset_from_node(cp); + return; + } + } +// Nothing to merge with, add it to the start of the free list +#ifdef DEBUG_FALLBACK_MALLOC + std::cout << " Making new free list entry " << offset_from_node ( cp ) << std::endl; +#endif + cp->next_node = offset_from_node ( freelist ); + freelist = cp; +} + +#ifdef INSTRUMENT_FALLBACK_MALLOC +size_t print_free_list () { + struct heap_node *p, *prev; + heap_size total_free = 0; + if ( NULL == freelist ) + init_heap (); + + for (p = freelist, prev = 0; + p && p != list_end; prev = p, p = node_from_offset (p->next_node)) { + std::cout << ( prev == 0 ? "" : " ") << "Offset: " << offset_from_node ( p ) + << "\tsize: " << p->len << " Next: " << p->next_node << std::endl; + total_free += p->len; + } + std::cout << "Total Free space: " << total_free << std::endl; + return total_free; + } +#endif +} // end unnamed namespace + +namespace __cxxabiv1 { + +#pragma GCC visibility push(hidden) + +void * __malloc_with_fallback(size_t size) { + void *ptr = std::malloc(size); + if (NULL == ptr) // if malloc fails, fall back to emergency stash + ptr = fallback_malloc(size); + return ptr; +} + +void * __calloc_with_fallback(size_t count, size_t size) { + void *ptr = std::calloc(count, size); + if (NULL != ptr) + return ptr; + // if calloc fails, fall back to emergency stash + ptr = fallback_malloc(size * count); + if (NULL != ptr) + std::memset(ptr, 0, size * count); + return ptr; +} + +void __free_with_fallback(void *ptr) { + if (is_fallback_ptr(ptr)) + fallback_free(ptr); + else + std::free(ptr); +} + +#pragma GCC visibility pop + +} // namespace __cxxabiv1 |