MIPS Assembly Language

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MIPS Assembly Language

• CPSC 321 Computer Architecture
• Andreas Klappenecker

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Addressing modes
lw s1, addr load s1 from addr lw s1,
8(s0) s1 Mems08 register s0 contains
the base address access the address
(s0) possibly add an offset 8(s0)
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Branch instructions
beqz s0, label if s00 goto label bnez s0,
label if s0!0 goto label bge s0, s1,
label if s0gts1 goto label ble s0, s1,
label if s0lts1 goto label blt s0,
s1, label if s0lts1 goto label beq s0,
s1, label if s0s1 goto label bgez
s0, s1, label if s0gt0 goto label
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Non-leaf procedures

• Suppose that a procedure procA calls another
  procedure jal procB
• Problem jal stores return address of procedure
  procB and destroys return address of procedure
  procA
• Save ra and all necessary variables onto the
  stack, call procB, and retore

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Stack
8(sp)
4(sp)
0(sp)

• The stack can be used for
• parameter passing
• storing return addresses
• storing result variables
• stack pointer sp

high address
stack pointer sp --gt
low address
sp sp - 12
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Factorial

• Compute n!
• Recall that
• 0! 1
• 1! 1
• n! n(n-1)!
• Store on the stack
• s0 n, the parameter
• ra, the return address

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factorial bgtz a0, doit if a0gt0 goto
generic case li v0, 1 base case, 0! 1
jr ra return doit sub sp,8 make
room for s0 and ra sw s0,(sp) store
argument s0n sw ra,4(sp) store return
address move s0, a0 save argument sub
a0, 1 factorial(n-1) jal factorial
v0 (n-1)! mul v0,s0,v0 n(n-1)! lw
s0,(sp) restore s0n lw ra,4(sp)
restore ra add sp,8 reduce stack size jr
ra return
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Fibonacci
fib(0) 0 fib(1) 1 fib(n) fib(n-1)
fib(n-2) 0, 1, 1, 2, 3, 5, 8, 13, 21,
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Fibonacci
li a0, 10 call fib(10) jal fib
move s0, v0 s0 fib(10) fib is a
recursive procedure with one argument a0 need to
store argument a0, temporary register s0 for
intermediate results, and return address ra
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fib subi sp,sp,12 save registers
on stack sw a0, 0(sp) save
a0 n sw s0, 4(sp) save
s0 sw ra, 8(sp) save return
address ra bgt a0,1, gen if
ngt1 then goto generic case move v0,a0
output input if n0 or n1 j
rreg goto restore
registers gen subi a0,a0,1
param n-1 jal fib
compute fib(n-1) move s0,v0
save fib(n-1) sub a0,a0,1
set param to n-2 jal fib
and make recursive call add v0, v0,
s0 v0 fib(n-2)fib(n-1) rreg lw
a0, 0(sp) restore registers from
stack lw s0, 4(sp)
lw ra, 8(sp) addi sp, sp,
12 decrease the stack size jr
ra
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Practice, practice, practice!!!

• Read Chapter 3 and Appendix A
• Write many programs and test them
• Get a thorough understanding of all assembly
  instructions
• Study the register conventions carefully