Fix GCC _sbrk allocation

Author: Deepika

platform/mbed_retarget.cpp

@@ -1245,16 +1245,17 @@ extern "C" int errno;
 // Weak attribute allows user to override, e.g. to use external RAM for dynamic memory.
 extern "C" WEAK caddr_t _sbrk(int incr)
 {
-    static  unsigned char *heap = (unsigned char *) &__end__;
-    unsigned char *prev_heap = heap;
-    unsigned char *new_heap = heap + incr;
+    static uint32_t heap = (uint32_t) &__end__;
+    uint32_t prev_heap = heap;
+    uint32_t new_heap = heap + incr;
 
     /* __HeapLimit is end of heap section */
-    if (new_heap >= (unsigned char *) &__HeapLimit) {
+    if (new_heap >= (uint32_t) &__HeapLimit) {
         errno = ENOMEM;
         return (caddr_t) -1;
     }
 
+    heap = new_heap;
     return (caddr_t) prev_heap;
 }
 #endif

rtos/TARGET_CORTEX/TOOLCHAIN_GCC_ARM/mbed_boot_gcc_arm.c

@@ -44,9 +44,9 @@ extern void __libc_init_array(void);
 void software_init_hook(void)
 {
     mbed_stack_isr_start = (unsigned char *) &__StackLimit;
-    mbed_stack_isr_size = ((uint32_t)((uint32_t) &__StackTop - (uint32_t) &__StackLimit));
+    mbed_stack_isr_size = (uint32_t) &__StackTop - (uint32_t) &__StackLimit;
     mbed_heap_start = (unsigned char *) &__end__;
-    mbed_heap_size = ((uint32_t)((uint32_t) &__HeapLimit - (uint32_t) &__end__));
+    mbed_heap_size = (uint32_t) &__HeapLimit - (uint32_t) &__end__;
 
     mbed_init();
     mbed_rtos_start();