A simple example (created by pruning down an NXP blinky example) shows malloc over-running heap and returning an invalid pointer. Obviously this corrupts memory in any non-trivial program.
KDS 3.2, Freedom K64F board.
Two bugs are illustrated:
- malloc is supposed to return NULL when no memory is available.
Please see: http://www.cplusplus.com/reference/cstdlib/malloc/
For embedded applications, a trap on out-of-memory would be better!
In no case is returning a pointer outside the heap acceptable.
- As shown in this example, the default heap size of 1kB (for a processor with 256kB RAM!)
in K64F example is too small for even a trivial RTL use, even before the application tries to use malloc.
NXP examples should set sensible default heap size!
Here's the relevant test code (complete project is attached):
// Quick-and-Dirty Blinky7 example for Freedom K64F
// Shows malloc memory over-run and return of invalid (non-NULL) pointer
// Debug only:
#include <stdio.h> // printf
#include <stdlib.h> // malloc
extern uint32_t __HeapBase;
extern uint32_t __HeapLimit;
printf("Hello there; this tests semi-hosting (and printf internally calls _malloc_r, and over-runs heap)\n");
void* pHeapBase = ((void*)&__HeapBase);
void* pHeapLimit= ((void*)&__HeapLimit);
void* pMalloc = malloc(16); // does malloc return something within expected heap area? Ooops: 0x200005c0
printf("Heap: base 0x%x, limit 0x%x, very first malloc 0x%x\n",pHeapBase, pHeapLimit, pMalloc);
// Prints: Heap: base 0x20000000, limit 0x20000400, very first malloc 0x200005c0
assert (pMalloc>=pHeapBase && pMalloc<pHeapLimit);
Original Attachment has been moved to: 20161228_malloc_overrun_demo.zip