No. Recall that a stack has a "last-in, first-out" organization. Unneeded memory is always popped from the top of the stack. Like a stack of plates, there are no holes underneath the top plate.
li $a0,xxx # $a0 contains the number of bytes you need.
# This must be a multiple of four.
li $v0,9 # code 9 == allocate memory
syscall # call the service.
# $v0 <-- the address of the first byte
# of the dynamically allocated block
A stack is an easily managed structure. Only a few memory addresses are needed to keep track of it. (Some of these addresses are in the stack pointer and in the frame pointer registers.) As a program executes, the stack grows and shrinks as subroutines are called and exited.
The heap is more like a book shelf. Books are constantly being taken off the shelf from various locations, leaving gaps, and then later returned, filling the gaps.
Here is how a SPIM program requests a block of memory from
SPIM's heap.
Use service code 9 to allocate a block of memory.
Put the number of bytes requested in $a0
You don't know in advance what range of addresses you will get
back for the allocate memory request.
The SPIM service returns the first address of a contiguous block of memory
in $a0.
(This is similar to a call to malloc() in C.)
In a full operating system, is there a service for deallocating memory, for returning a previously allocated block to the system?