在bootcard中有流程是heap的初始化，为了更详细的了解内存初始化，这里以_Heap_Initialize为入口，详细了解具体做了什么
我们之前分析流程的时候，可以知道RTEMS初始化了多个堆，主要如下
_Workspace_Handler_initialization 会初始化_Heap_Initialize _Malloc_Initialize 会初始化 _Heap_Initialize add_area的cache_coherent_heap会初始化_Heap_Initialize
总共三个heap区，本文以malloc为例关注_Heap_Initialize 的初始化
uintptr_t _Heap_Initialize( Heap_Control *heap, void *heap_area_begin_ptr, // 起始地址 uintptr_t heap_area_size, // 大小 uintptr_t page_size ) { Heap_Statistics *const stats = &heap->stats; uintptr_t const heap_area_begin = (uintptr_t) heap_area_begin_ptr; uintptr_t const heap_area_end = heap_area_begin + heap_area_size; uintptr_t first_block_begin = 0; uintptr_t first_block_size = 0; uintptr_t last_block_begin = 0; uintptr_t min_block_size = 0; bool area_ok = false; Heap_Block *first_block = NULL; Heap_Block *last_block = NULL; // 如果page_size 没有设置，则设置为cpu对齐大小，否则按照设置大小向cpu对齐 if ( page_size == 0 ) { page_size = CPU_ALIGNMENT; } else { page_size = _Heap_Align_up( page_size, CPU_ALIGNMENT ); if ( page_size < CPU_ALIGNMENT ) { /* Integer overflow */ return 0; } } // 计算最小的块大小 min_block_size = _Heap_Min_block_size( page_size ); // 获取第一个块和最后一个块的地址 area_ok = _Heap_Get_first_and_last_block( heap_area_begin, heap_area_size, page_size, min_block_size, &first_block, &last_block ); if ( !area_ok ) { return 0; } memset(heap, 0, sizeof(*heap)); #ifdef HEAP_PROTECTION heap->Protection.block_initialize = _Heap_Protection_block_initialize_default; heap->Protection.block_check = _Heap_Protection_block_check_default; heap->Protection.block_error = _Heap_Protection_block_error_default; #endif // 计算第一个块的大小，拿最后一个块的开始减去第一个块的开始 first_block_begin = (uintptr_t) first_block; last_block_begin = (uintptr_t) last_block; first_block_size = last_block_begin - first_block_begin; // 设置第一个块，结合block的结构体，将prev_size设置为堆的末尾 // 将第一个块的next设置为空闲链表的尾，prev设置为空闲链表的头，这里相当于初始化空闲链表 /* First block */ first_block->prev_size = heap_area_end; first_block->size_and_flag = first_block_size | HEAP_PREV_BLOCK_USED; first_block->next = _Heap_Free_list_tail( heap ); first_block->prev = _Heap_Free_list_head( heap ); _Heap_Protection_block_initialize( heap, first_block ); // 报错堆的信息，如页大小，最小块大小，堆范围，第一个块地址，最后一个块地址 // 设置空闲链表的第一个元素是first_block /* Heap control */ heap->page_size = page_size; heap->min_block_size = min_block_size; heap->area_begin = heap_area_begin; heap->area_end = heap_area_end; heap->first_block = first_block; heap->last_block = last_block; _Heap_Free_list_head( heap )->next = first_block; _Heap_Free_list_tail( heap )->prev = first_block; // 将最后一个blokc的prev_size设置为第一个block的size /* Last block */ last_block->prev_size = first_block_size; last_block->size_and_flag = 0; _Heap_Set_last_block_size( heap ); _Heap_Protection_block_initialize( heap, last_block ); // 统计信息 总大小，空闲大小，块数 /* Statistics */ stats->size = first_block_size; stats->free_size = first_block_size; stats->min_free_size = first_block_size; stats->free_blocks = 1; stats->max_free_blocks = 1; _Heap_Protection_set_delayed_free_fraction( heap, 2 ); _HAssert( _Heap_Is_aligned( heap->page_size, CPU_ALIGNMENT ) ); _HAssert( _Heap_Is_aligned( heap->min_block_size, page_size ) ); _HAssert( _Heap_Is_aligned( _Heap_Alloc_area_of_block( first_block ), page_size ) ); _HAssert( _Heap_Is_aligned( _Heap_Alloc_area_of_block( last_block ), page_size ) ); // 返回第一个块的大小 return first_block_size; }
代码中有注释，我们可以知道，对于heap初始化来说，其主要是构造了Heap_Control *heap结构体，然后计算Heap_Block的大小来分配每个block，并为每个block来构造block信息，最后设置heap的统计信息。
根据gdb我们可以观察heap构造情况，首先查看heap control结构体,结构体定义如下：
struct Heap_Control { Heap_Block free_list; uintptr_t page_size; uintptr_t min_block_size; uintptr_t area_begin; uintptr_t area_end; Heap_Block *first_block; Heap_Block *last_block; Heap_Statistics stats; #ifdef HEAP_PROTECTION Heap_Protection Protection; #endif };
实际信息如下
(gdb) p _Malloc_Heap $1 = {free_list = {prev_size = 0, size_and_flag = 0, next = 0x0, prev = 0x0}, page_size = 0, min_block_size = 0, area_begin = 0, area_end = 0, first_block = 0x0, last_block = 0x0, stats = {lifetime_allocated = 0, lifetime_freed = 0, size = 0, free_size = 0, min_free_size = 0, free_blocks = 0, max_free_blocks = 0, used_blocks = 0, max_search = 0, searches = 0, allocs = 0, failed_allocs = 0, frees = 0, resizes = 0}}(gdb) p _Malloc_Heap $2 = {free_list = {prev_size = 0, size_and_flag = 0, next = 0x1342a0, prev = 0x1342a0}, page_size = 16, min_block_size = 32, area_begin = 1262239, area_end = 1072431104, first_block = 0x1342a0, last_block = 0x3febfff0, stats = { lifetime_allocated = 0, lifetime_freed = 0, size = 1071168848, free_size = 1071168848, min_free_size = 1071168848, free_blocks = 1, max_free_blocks = 1, used_blocks = 0, max_search = 0, searches = 0, allocs = 0, failed_allocs = 0, frees = 0, resizes = 0}}
heap block结构体如下
struct Heap_Block { uintptr_t prev_size; uintptr_t size_and_flag; Heap_Block *next; Heap_Block *prev; };
实际信息如下
(gdb) p *(Heap_Block *)0x1342a0 $5 = {prev_size = 1072431104, size_and_flag = 1071168849, next = 0x102c90 <_Malloc_Heap>, prev = 0x102c90 <_Malloc_Heap>}(gdb) p *(Heap_Block *)0x3febfff0 $6 = {prev_size = 1071168848, size_and_flag = 18446744072638382768, next = 0x0, prev = 0x0}
heap statistics结构体如下
typedef struct { /** * @brief Lifetime number of bytes allocated from this heap. * * This value is an integral multiple of the page size. */ uint64_t lifetime_allocated; /** * @brief Lifetime number of bytes freed to this heap. * * This value is an integral multiple of the page size. */ uint64_t lifetime_freed; /** * @brief Size of the allocatable area in bytes. * * This value is an integral multiple of the page size. */ uintptr_t size; /** * @brief Current free size in bytes. * * This value is an integral multiple of the page size. */ uintptr_t free_size; /** * @brief Minimum free size ever in bytes. * * This value is an integral multiple of the page size. */ uintptr_t min_free_size; /** * @brief Current number of free blocks. */ uint32_t free_blocks; /** * @brief Maximum number of free blocks ever. */ uint32_t max_free_blocks; /** * @brief Current number of used blocks. */ uint32_t used_blocks; /** * @brief Maximum number of blocks searched ever. */ uint32_t max_search; /** * @brief Total number of searches. */ uint32_t searches; /** * @brief Total number of successful allocations. */ uint32_t allocs; /** * @brief Total number of failed allocations. */ uint32_t failed_allocs; /** * @brief Total number of successful frees. */ uint32_t frees; /** * @brief Total number of successful resizes. */ uint32_t resizes; } Heap_Statistics;
实际信息在heap结构体已经打印，这里摘出来如下
(gdb) p _Malloc_Heap->stats $10 = {lifetime_allocated = 0, lifetime_freed = 0, size = 0, free_size = 0, min_free_size = 0, free_blocks = 0, max_free_blocks = 0, used_blocks = 0, max_search = 0, searches = 0, allocs = 0, failed_allocs = 0, frees = 0, resizes = 0}(gdb) p _Malloc_Heap->stats $11 = {lifetime_allocated = 0, lifetime_freed = 0, size = 1071168848, free_size = 1071168848, min_free_size = 1071168848, free_blocks = 1, max_free_blocks = 1, used_blocks = 0, max_search = 0, searches = 0, allocs = 0, failed_allocs = 0, frees = 0, resizes = 0}
至此，我们清楚的知道了RTEMS系统的堆的初始化方式。后续调试堆的时候，这些结构体对我们非常有用