malloc 什么时候在裸机环境中返回 NULL? [英] When does malloc return NULL in a bare-metal environment?

问题描述

有一个c内存模型如下:

There is a c memory model as following :

      +--------+   Last Address of RAM
      | Stack  |
      |   |    |
      |   v    |
      +--------+
RAM   |        |
      |        |
      +--------+
      |   ^    |
      |   |    |
      | Heap   |
      +--------+
      |   ZI   |
      +--------+
      |   RW   |  
      +========+  First Address of RAM

堆栈和堆空间以相反的方向增加.它们将在中间相互重叠.所以我的问题是:

The stack and heap space increase in opposite directions. They would be overlapped with each other in the middle. So my questions are:

• 在裸机环境中，malloc 什么时候返回 NULL?
• 在裸机环境下，如何防止栈与堆重叠?

推荐答案

@WikiWang 是正确的，如果您使用的是静态的编译时内存布局(edit 尽管您必须告诉您的 malloc 以某种方式实现堆的末尾).

@WikiWang is correct if you are using a static, compile-time memory layout (edit although you have to tell your malloc implementation somehow where the end of the heap is).

如果不是，并且假设您是指裸机，这取决于您的板支持包中的 C 库实现.该库必须提供 brk(2) 或具有类似效果的功能.malloc 在 brk 或 sbrk 设置的内存区域内工作.例如，参见 malloc 源码调用宏 MORECORE，默认为 sbrk.您的 C 库将不得不使用内核调用以外的其他东西:).

If not, and assuming you mean bare-metal, it depends on the C library implementation in your board-support package. The library must provide some implementation of brk(2) or a function having a similar effect. malloc works within the area of memory set by brk or sbrk. For example, see the malloc source calling macro MORECORE, which is by default sbrk. Your C library will have to use something other than a kernel call for that :) .

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