The answers to the questions below are found in this
x86 assembly guide by David Evans at the University of Virginia. Note that
this homework covers x86. You will be
coding in x86-64 assembler. There are important extensions
to x86-64 but you should understand a little about the x86 ISA
before jumping in to x86-64.
This Tiny Guide is enough for this homework.
--------------------------------------------------------------------- Due Friday Will be collected Friday night.
Create a text file on Odin named 2240/9/a9.txt
Answer all the questions.
Choose 2 questions
Tell me what you learned.
Put them at the top. ---------------------------------------------------------------------
1. What are the ESP and the EBP registers in x86 assembly used for?
2. The 6 general purpose registers (GPRs) in x86 are EAX, EBX, ECX, EDX,
ESI, & EDI. There are
also sub-registers. For example, explain
the difference between the EAX, AX, AH and AL registers.
Give the size of each.
3. Describe what these declarations in the static data segment accomplish.
Note that in x86 a word is 2 bytes and a double word is 4 bytes.
.DATA
var DB 64
var2 DB ?
DB 10
X DW ?
Y DD 3000
4. The DUP assembler directive duplicates an initialization. Explain these:
Z DD 1, 2, 3
bytes DB 10 DUP(?)
arr DD 100 DUP(0)
str DB 'hello',0
5. Unlike MIPS, x86 supports direct accesses to memory. Note that
a WORD is
2 bytes and a DWORD is 4 bytes. The x86 registers EAX, EBX, ECX, EDX,
ESI, EDI, ESP, and EBP are 32-bit. Also note that with x86, data movement
is always from right to left (there is no operation
equivalent to the store operation in x86). With these facts in mind,
explain the instructions below.
6. The MOV instruction supports register to memory, register to register or
memory to register. Explain these:
mov eax, ebx
mov byte ptr [var], 5
7. The push instruction places its operand onto the top of the hardware
supported stack in memory. Push first decrements ESP by 4 (bytes),
then places
its operand into the contents of the 32-bit location at address [ESP].
ESP (the stack pointer) is decremented by push first since the x86 stack
grows from high to low addresses. Explain these instructions:
push eax
push [var]
8. The pop instruction copies 4 bytes from the top of the
hardware stack at address SP to register or memory. SP is
then incremented by 4. Explain these instructions:
pop edi
pop [ebx]
9. The Load Effective Address instruction (lea)
grabs the address of a label/symbol or computes an
address by adding an offset. The effective address is then loaded into the
target register. Explain these:
lea eax, [var]
lea edi, [ebx+4*esi]
10. Unlike MIPS, arithmetic operations in x86
can be performed register to register or register to
memory. The second operand may be a constant. Explain these:
add eax, 10
add BYTE PTR [var], 10
sub al, ah
imul eax, [var]
imul esi, edi, 25
11. Explain each of these inc and dec instructions.
What do the instructions do?
dec eax
inc DWORD PTR [var]
12. Integer division utilizes a 64-bit register EDX:EAX (where EDX is the
most significant 32 bits). The idiv instruction divides the contents of
EDX:EAX by the operand. The quotient is stored into EAX and the
remainder in EDX. Explain these operations:
idiv ebx
idiv DWORD PTR [var]
13. The bitwise logical AND, OR and EXCLUSIVE OR instructions perform the
operation on the first register place the result in the first register.
Explain these operations:
and eax, 0fH # 0fH is 15 in decimal - the H denotes hex
xor edx, edx
neg edx
not edx
14. The Shift Left and Shift Right instructions perform shifts on the first
operand, padding empty bit positions with zeros. The second operand is
either an 8-bit constant or the register CL. Explain these shift operations:
shl eax,1
shr ebx,cl
15. In x86, what does the instruction pointer (IP) register hold?
16. The unconditional jump instruction jumps to the given label. The
conditional jump instruction jumps based on the contents of a condition
bit in the machine status word register. This bit is set to 0 or 1 in the
instruction prior to the conditional jump. Explain the control flow
instructions below assuming that each is preceeded by
cmp eax, ebx:
jump L1
jle done
je L1
jge L1
17. The Compare (cmp) instruction compares the values of two operands and sets
the condition codes in the machine status word appropriately. The
result can then be used to facilitate a jump. Explain these: