typedef struct _heap_info { mstate ar_ptr; /* Arena for this heap. */ struct _heap_info *prev; /* Previous heap. */ size_t size; /* Current size in bytes. */ size_t mprotect_size; /* Size in bytes that has been mprotected PROT_READPROT_WRITE. */ /* Make sure the following data is properly aligned, particularly that sizeof (heap_info) + 2 * SIZE_SZ is a multiple of MALLOC_ALIGNMENT. */ char pad[-6 * SIZE_SZ & MALLOC_ALIGN_MASK]; } heap_info;
每一个新开辟的堆都有一个独立的heap_info结构体
ar_ptr指针指向一个为该堆服务的arena
prev指针指向上一个堆的heap_info结构体
size记录了堆的大小
mprotect_size记录了堆中多大的空间是可读写的
pad字符串则用以堆其该结构体，使其能够按照0x10字节对齐(x86中则是8字节对齐)
这里引用CTF-WIKI中对pad的解释：
pad 里负数的缘由是什么呢？
pad 是为了确保分配的空间是按照 MALLOC_ALIGN_MASK+1 (记为 MALLOC_ALIGN_MASK_1) 对齐的。在 pad 之前该结构体一共有 6 个 SIZE_SZ 大小的成员, 为了确保 MALLOC_ALIGN_MASK_1 字节对齐, 可能需要进行 pad，不妨假设该结构体的最终大小为 MALLOC_ALIGN_MASK_1*x，其中 x 为自然数，那么需要 pad 的空间为 MALLOC_ALIGN_MASK_1 * x - 6 * SIZE_SZ = (MALLOC_ALIGN_MASK_1 * x - 6 * SIZE_SZ) % MALLOC_ALIGN_MASK_1 = 0 - 6 * SIZE_SZ % MALLOC_ALIGN_MASK_1=-6 * SIZE_SZ % MALLOC_ALIGN_MASK_1 = -6 * SIZE_SZ & MALLOC_ALIGN_MASK
/* Set if the fastbin chunks contain recently inserted free blocks. */ /* Note this is a bool but not all targets support atomics on booleans. */ int have_fastchunks;
/* Fastbins */ mfastbinptr fastbinsY[NFASTBINS];
/* Base of the topmost chunk -- not otherwise kept in a bin */ mchunkptr top;
/* The remainder from the most recent split of a small request */ mchunkptr last_remainder;
/* Normal bins packed as described above */ mchunkptr bins[NBINS * 2 - 2];
/* Bitmap of bins */ unsigned int binmap[BINMAPSIZE];
/* Linked list */ struct malloc_state *next;
/* Linked list for free arenas. Access to this field is serialized by free_list_lock in arena.c. */ struct malloc_state *next_free;
/* Number of threads attached to this arena. 0 if the arena is on the free list. Access to this field is serialized by free_list_lock in arena.c. */ INTERNAL_SIZE_T attached_threads;
/* Memory allocated from the system in this arena. */ INTERNAL_SIZE_T system_mem; INTERNAL_SIZE_T max_system_mem; };
/* FASTCHUNKS_BIT held in max_fast indicates that there are probably some fastbin chunks. It is set true on entering a chunk into any fastbin, and cleared only in malloc_consolidate. The truth value is inverted so that have_fastchunks will be true upon startup (since statics are zero-filled), simplifying initialization checks. */
/* NONCONTIGUOUS_BIT indicates that MORECORE does not return contiguous regions. Otherwise, contiguity is exploited in merging together, when possible, results from consecutive MORECORE calls. The initial value comes from MORECORE_CONTIGUOUS, but is changed dynamically if mmap is ever used as an sbrk substitute. */
/* ARENA_CORRUPTION_BIT is set if a memory corruption was detected on the arena. Such an arena is no longer used to allocate chunks. Chunks allocated in that arena before detecting corruption are not freed. */
/* Memory map support */ int n_mmaps; int n_mmaps_max; int max_n_mmaps; /* the mmap_threshold is dynamic, until the user sets it manually, at which point we need to disable any dynamic behavior. */ int no_dyn_threshold;
/* First address handed out by MORECORE/sbrk. */ char *sbrk_base;
#if USE_TCACHE /* Maximum number of buckets to use. */ size_t tcache_bins; size_t tcache_max_bytes; /* Maximum number of chunks in each bucket. */ size_t tcache_count; /* Maximum number of chunks to remove from the unsorted list, which aren't used to prefill the cache. */ size_t tcache_unsorted_limit; #endif };
