MIT6.S081笔记：lecture 5

MIT6.S081笔记：lecture 5 calling conventions and stack

Calling convenstions

RISC-V Register File

Integer Instructions

• lb t0, 8(sp)

  loads from memory address (sp+8) into register t0

  lb = load byte, lh = load halfword, lw = load word, ld = load doubleword

• add a0, t0, t1

  adds value of t0 to the value of t1 and stores the sum into a0

• addi a0, t0, -10

  adds value of t0 to the value -10 and stores the sum into a0

• mul a0, t0, t1

  multiplies the value of t0 to the value of t1 and stores the product int a0

Pseudo Instructions

• translate to real instructions by assembler

Branching Instructions

• a way to jump to different parts of your code
• Branching refers to the “conditional jump” instructions, such as beq, bne, bgt, bge, blt, ble for branch-if equals, not equals, greater than, greater than or equals, less than, and less than or equals, respectively.

# t0 = 0
li      t0, 0
li      t2, 10
loop_head:
bge     t0, t2, loop_end
# Repeated code goes here
addi    t0, t0, 1
j		loop_head
loop_end:

Stack

Stack frame

• stack frame is generated by function calls

• start from high addresses and grow downwards to low addresses

• the return address and to prev frame pointer are at a predictable position

• sp - bottom of the stack

• fp - top of the current frame

Use backtrace to debug