4-3
PROCEDURE CALLS, INTERRUPTS, AND EXCEPTIONS
4.2.1.Setting Up a Stack
To set a stack and establish it as the current stack, the program or operating system/executive
must do the following:
1.Establish a stack segment.
2.Load the segment selector for the stack segment into the SS register using a MOV, POP, or
LSS instruction.
3.Load the stack pointer for the stack into the ESP register using a MOV, POP, or LSS
instruction. (The LSS instruction can be used to load the SS and ESP registers in one
operation.)
Refer to Chapter 3, Protected-Mode Memory Management of the Intel Architecture Software
Developers Manual, Volume 3, for information on how to set up a segment descriptor and
segment limits for a stack segment.
4.2.2.Stack Alignment
The stack pointer for a stack segment should be aligned on 16-bit (word) or 32-bit (double-word)
boundaries, depending on the width of the stack segment. The D flag in the segment descriptor
for the current code segment sets the stack-segment width (refer to Chapter 3, Protected-Mode
Memory Management of the Intel Architecture Software Developers Manual, Volume 3). The
PUSH and POP instructions use the D flag to determine how much to decrement or increment
the stack pointer on a push or pop operation, respectively. When the stack width is 16 bits, the
stack pointer is incremented or decremented in 16-bit increments; when the width is 32 bits, the
stack pointer is incremented or decremented in 32-bit increments.
The processor does not check stack pointer alignment. It is the responsibility of the programs,
tasks, and system procedures running on the processor to maintain proper alignment of stack
pointers. Misaligning a stack pointer can cause serious performance degradation and in some
instances program failures.
4.2.3.Address-Size Attributes for Stack Accesses
Instructions that use the stack implicitly (such as the PUSH and POP instructions) have two
address-size attributes each of either 16 or 32 bits. This is because they always have the implicit
address of the top of the stack, and they may also have an explicit memory address (for example,
PUSH Array1[EBX]). The attribute of the explicit address is determined by the D flag of the
current code segment and the presence or absence of the 67H address-size prefix, as usual.
The address-size attribute of the top of the stack determines whether SP or ESP is used for the
stack access. Stack operations with an address-size attribute of 16 use the 16-bit SP stack pointer
register and can use a maximum stack address of FFFFH; stack operations with an address-size
attribute of 32 bits use the 32-bit ESP register and can use a maximum address of FFFFFFFFH.
The default address-size attribute for data segments used as stacks is controlled by the B flag of
