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1 CSE 2021: Computer Organization Le
CSE 2021: Computer Organization Lecture - 6 Code Translation - 4 Review & Exercises Shakil M. Khan MIPS Assembly Language (Summary) • 32X32 bits Registers ( $s0 - $s7 , $t0 - $t9 , $zero , …) • Arithmetic and logical instructions ( add , sub , mult , div , slt , sll , srl , sra , the i / u / v suffix)

2 • Jump and branch ( j , beq , bne )
• Jump and branch ( j , beq , bne ) • Load and store ( lb , lh , lw , sb , sw , sh , the u suffix) • I/O ( syscall ) • Static attributes and .data (directives: .byte , .half , .word , . ascii , . asciiz , .space ), . globl , .text • Procedures ( jal , jr , $v0 - $v1 , $a0 - $a3 , $ ra ) • Stack ( $sp ,

3 $ fp ) • Heap ( syscall 9) • l
$ fp ) • Heap ( syscall 9) • lui , mfhi , mflo , … • Some pseudo - instructions ( la , mul , …) CSE - 2021 2 MIPS Assembly Language (Summary) • MIPS instruction formats ( R - type , I - type , J - type ) • MIPS addressing modes ( immediate , register , base , PC - relative , pseudo - direct ) • Concurrent data

4 access ( ll , sc ) • Translating (
access ( ll , sc ) • Translating (compiler + assembly) and object files • Linking (static vs. dynamic) and loading CSE - 2021 3 Pseudo Instructions • Not real, merely conveniences added by the assembler • Not portable: have no machine language encoding • Examples: – mul mult + mfhi – nop sll $0, $0, 0 â

5 €“ li / la ori + lui – abs s
€“ li / la ori + lui – abs slt + beq + sub + $at – move add + $zero – blt slt + bne + $at • Do NOT use pseudo in this course! CSE - 2021 4 Exercise 1 • Method pofu ( p roduct o ver f low u nsigned) detects O/F in the mult of unsigned integers. It takes two integers in $a0 and $a1 and

6 returns $v0 = 0 or 1 if $a0*$a1 fits or
returns $v0 = 0 or 1 if $a0*$a1 fits or does not fit in 32 bits. Is it correct? If not, fix it. CSE - 2021 5 pofu : multu $a0, $a1 mfhi $t0 beq $t0, $0, fits addi $v0, $0, 1 fits: add $v0, $0, $0 jr $ ra Exercise 2 • Method pof is similar to pofu except it deals wit

7 h signed integers. One quick way to imp
h signed integers. One quick way to implement pof would be to copy and paste pofu and then replace the label pofu with pof and the instruction multu with mult . Would this be correct? If not, fix it. CSE - 2021 6 Exercise 3(a) • lib.s (below) was loaded with .text at 0x0040002C and .data at 0x10010000 . What is

8 the address of x ? CSE - 2021 7
the address of x ? CSE - 2021 7 . globl x . globl ch .data x: .byte 3 y: .word 4 .text ch : lw $v0, y($0) jr $ ra Exercise 3(b) • lib.s (below) was loaded with .text at 0x0040002C and .data at 0x10010000 . What is the address of y ? Why? CS

9 E - 2021 8 . globl x
E - 2021 8 . globl x . globl ch .data x: .byte 3 y: .word 4 .text ch : lw $v0, y($0) jr $ ra Exercise 3(c) • lib.s (below) was loaded with .text at 0x0040002C and .data at 0x10010000 . What is the address of ch ? CSE - 2021 9 . globl

10 x . globl ch
x . globl ch .data x: .byte 3 y: .word 4 .text ch : lw $v0, y($0) jr $ ra Exercise 4(a) • The file app.s (below) was loaded immediately after lib.s . What is the address of main ? • hint : the assembler replaces lw / sw with several instructions

11 CSE - 2021 10 .text main
CSE - 2021 10 .text main: sw $ ra , 0($sp) addi $sp, $sp, - 4 jal ch lb $t0, x($0) Exercise 4(b) • The file app.s (below) was loaded immediately after lib.s . What is the machine language encoding of the instruction: jal ch ? CSE - 2021 11 .text main: sw

12 $ ra , 0($sp) addi
$ ra , 0($sp) addi $sp, $sp, - 4 jal ch lb $t0, x($0) Exercise 5 • Argue that stack allocations are not likely to cause memory leaks but that heap allocations are CSE - 2021 12 • Factors : – scope in which push/pop appear versus allocate/de - allocate – consequences of imbalanced

13 push/pop versus a missing de - allocat
push/pop versus a missing de - allocate Exercise 6 • Assume that the word 0x01048025 represents an instruction. What is the corresponding assembly language instruction? Your answer must use register names, e.g. $t0 , not register numbers, and must specify immediates in decimal, not binary. CSE - 2021 13 Exercise 7 • To ha

14 ndle a large 32 - bit immediate X , we
ndle a large 32 - bit immediate X , we replace with the four instructions below: • Why can’t the second be addi instead of ori ? • Can we do better (three instructions)? CSE - 2021 14 lw $t0, X($a0) lui $at, upper16_X ori $at, $at, lower16_X add $at, $at, $a0 lw $t0, 0($at) Exercise 8

15 • Given the utility class:
• Given the utility class: What are the outputs of the following apps: CSE - 2021 15 . globl work .text work: slt $t0, $a0, $a1 bne $t0, $0, less add $v0, $a0, $a1 j done less: sub $v0, $a0, $a1 done: jr $ ra Exercise 8(a) CSE - 202

16 1 16 .text main: sw
1 16 .text main: sw $ ra , 0($sp) addi $sp, $sp, - 4 addi $a0, $0, 3 addi $a1, $0, 8 jal work add $a0, $v0, $0 addi $v0, $0, 1 syscall addi $sp, $sp, 4 lw $ ra , 0($sp) jr $ ra Exercise 8(

17 b) CSE - 2021 17 .text
b) CSE - 2021 17 .text main: sw $ ra , 0($sp) addi $sp, $sp, - 4 addi $a0, $0, 36 addi $a1, $0, 8 jal work add $a0, $v0, $0 addi $v0, $0, 1 syscall addi $sp, $sp, 4 lw $ ra , 0($sp) jr $

18 ra Exercise 9(a) • What is the va
ra Exercise 9(a) • What is the value of $s0 after executing label A ? • Write down the value of $s1 after executing label B CSE - 2021 18 .data x: .word 10 y: .byte 4, 3, 2 p: .word y .text main: addi $t0, $0, - 4 A: lw $s0, p($t0) addi $t0, $0, 3 B: lb $s1, y($t0)

19 jr $ ra Exercise 9(b) â€
jr $ ra Exercise 9(b) • What is the value of $s2 after executing label D ? • What is the value of $s3 after executing label E ? CSE - 2021 19 .data x: .word 10 y: .byte 4, 3, 2 p: .word y .text main: addi $t0, $0, 1 addi $s2, $0, - 3 C: sb $s2, y($t0) D:

20 lb $s2, y($t0) E: lbu $s3, y(
lb $s2, y($t0) E: lbu $s3, y($t0) jr $ ra Exercise 10(a) • Write the method clone that copies a given array of bytes to a new array. Specifically, it receives in $a0 the number of elements in the array and in $a1 the address of its first element. The method should allocate enough space on the heap to store the copy and then copy

21 the array and return in $v0 the addr
the array and return in $v0 the address of the first element of the copy. CSE - 2021 20 Exercise 10(b) • Write a main method that: – uses clone to copy array1 to the heap – copies the content of the heap to array2 (cf. posted programs on the web) CSE - 2021 21 .data array1: .byte 1,2,11,4,5