Re: malloc always returns null

[Ted Phares <tphares at ybad dot com>]

> NEWLIB requires the underlying function: "_sbrk" - in syscalls, In "OS" 
> type environment, SBRK would call the operating system requesting more 
> memory.
>
> In an embedded system using NEWLIB - the SBRK function has (a) a pointer 
> to the current end of the heap, it sort of works like this:
> Newlib impliments it this way:  (newlib source, libgloss, arm, syscalls.c)
>
> You want to set a break point at _sbrk - and step through the code.
> Examine the addresses of variables as you do this.

Thank you, Duane.  You hit the nail on the head:  sbrk()'s check for 
stack-heap collision was failing, because the user stack area happened 
to be set up ahead of the heap area in my memory map.  I set up the more 
conventional arrangement where the heap & stack grow toward each other, 
and now malloc() is working.

Thanks again,

-ted