Why was a malloc with heap_size = 0 successful?

RE: Why was a malloc with heap_size = 0 successful?

Håkon Alseth — Fri, 18 Aug 2017 08:54:54 GMT

Hi! The mem-manager has checks for > 0 && < max_block_size: infocenter.nordicsemi.com/.../lib_mem_manager.html

We tend to avoid dynamic memory allocation, unless absolutely needed, as there are many "gotcha's" with it, like memory fragmentation etc. Unfortunately, I have little to no experience with dynamic allocation on embedded platforms, so I cannot give a recommendation on which library you should use.

Cheers, Håkon

RE: Why was a malloc with heap_size = 0 successful?

Ken — Thu, 17 Aug 2017 14:30:22 GMT

We are using the default libnosys, so that explains why it was successful. Should we be using the malloc functions from nordic's mem_manager library rather than the libnosys malloc functions. Would this add the heap overflow protection?

Or Is there a better nordic recommended library for use with the GCC compiler?

RE: Why was a malloc with heap_size = 0 successful?

Håkon Alseth — Thu, 17 Aug 2017 13:15:05 GMT

What compiler/stdlib are you using? malloc is normally provided by an in-built library, unless you're brave and declare your own.

I know that the malloc implementation in libnosys (-lnosys in your linker file, if using GCC) does not have any overflow check in function _sbrk(), so if you're using GCC + nosys; this will happen and it will most likely eat out of the bottom of the .stack. Here's the _sbrk() from libnosys, which basically has no checks: github.com/.../sbrk.c

Cheers, Håkon