1. Memory Segments Code (.code) Data (.data) Stack Heap
contains user program
Data (.data)
contains fixed program data
Stack
maintains parameters, local variables, return code for functions
Heap
program data
storage is allocated at runtime
Note: Heap and Stack grow towards each other
Irvine, Kip R. Assembly Language for x86 Processors 7/e, 2015.

2. Dynamic Memory Allocation
Reserving memory at runtime for objects
aka heap allocation
standard in high-level languages (C++, Java)
HLL’s have built-in “heap managers”
Heap manager
allocates large blocks of memory
maintains free list of pointers to smaller blocks
manages requests by programs for storage
C++ example - allocate an integer array at run time:
int size;
cin >> size;
int array[] = new int[size];
Irvine, Kip R. Assembly Language for x86 Processors 7/e, 2015.

3. Windows Heap-Related Functions
Irvine, Kip R. Assembly Language for x86 Processors 7/e, 2015.

4. Sample Code Allocate block of memory from existing heap: .data
hHeap HANDLE ? ; heap handle
pArray DWORD ? ; pointer to array
.code
push 1000
push HEAP_ZERO_MEMORY
push hHeap
call HeapAlloc
cmp eax,0
jne OK
jmp DONE
OK: mov pArray,eax ; save the pointer
DONE:
Flag settings
(set to all zero’s)
Irvine, Kip R. Assembly Language for x86 Processors 7/e, 2015.

5. Sample Code
Free a block of memory previously created by calling HeapAlloc:
.data
hHeap HANDLE ? ; heap handle
pArray DWORD ? ; pointer to array
.code
push pArray
push 0
push hHeap
call HeapFree ; eax will be non-zero if successful!
Example : Heaptest
Irvine, Kip R. Assembly Language for x86 Processors 7/e, 2015.