Keil MDK 使用malloc()&free()，stm32简单测试可用

爱被打了一巴掌 2022-05-31 02:08 383阅读 0赞

### 1.8.9 Using malloc() when exploiting the C library ###

If heap support is required for bare machine C, you must implement `_init_alloc()` and`__rt_heap_extend()`.

`_init_alloc()` must be called first to supply initial heap bounds, and `__rt_heap_extend()` must be provided even if it only returns failure. Without `__rt_heap_extend()`, certain library functionality is included that causes problems when you are writing bare machine C.

Prototypes for both `_init_alloc()` and `__rt_heap_extend()` are in rt\_heap.h.

以上摘自http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.subset.swdev.comp6/index.html

程序包含头文件：rt\_heap.h,stdlib.h。注意不要勾选MicroLIB。

汇编代码中设置Heap大小，我设置为4KB。

Heap\_Size EQU 0x00004000

跟高级的方法如下：  
![Center][]

简单的测试代码如下：

**\[cpp\]** [view plain][] [copy][view plain]

1.  \#define HEAP\_BASE 0x20002558
2.  \#define HEAP\_SIZE 0x00004000
3.  \#define HEAP\_END HEAP\_BASE+HEAP\_SIZE
4.  void testmem() 
5.   \{ 
6.  int \*p,\*k=NULL; 
7.  int a=0; 
8.  volatileint i=0; 
9.   \_init\_alloc(HEAP\_BASE,HEAP\_END); 
10. while(1) 
11.  \{ 
12. if(a>1000)break; 
13.  p=(int\*)malloc(a++); 
14.  i=(unsigned int)p-(unsigned int)k; 
15.  k=p; 
16.  \*p=a; 
17. 
18. //free(p);
19.  \} 
20. 
21.  \}

调试可看到如下结果：

![Center 1][]

其中p,k是两次malloc得到的地址，i为两次得到的mallac得到地址的间隔，需要注意malloc得到的内存是8字节对其的。a是写入的一个数据。该程序执行一段时间后会内存泄漏，因为没free,去掉free()的注释即可。以下是free（p）的调试结果：经过多次malloc后得到的内存地址始终是0x20002570。

![Center 2][]

总结：

1.  .If heap support is required for bare machine C, you must implement `_init_alloc()` and`__rt_heap_extend()`.  
    
2.  分配的内存地址8byte对齐;
3.  \#define HEAP\_BASE 0x20002558这里的地址可以看\*.map文件Heap\_Mem的值。这里应该可以通过汇编和C的混合编程来实现，暂时没试。

饿死了，以上暂作笔记用，找时间再整理下测试下

转自：[http://blog.csdn.net/janosong/article/details/50222327][http_blog.csdn.net_janosong_article_details_50222327]

[Center]: /images/20220531/df4b7e3519da441b8543ee08508f417c.png
[view plain]: http://blog.csdn.net/janosong/article/details/50222327#
[Center 1]: /images/20220531/f027e6495da848eb9facfd2bf6d7172e.png
[Center 2]: /images/20220531/670e9381723a4c7893c3f0bd5147de41.png
[http_blog.csdn.net_janosong_article_details_50222327]: http://blog.csdn.net/janosong/article/details/50222327