Last updated April 10, 2022

Status: Tags: #cards/cmpt295/assembly Links: x86-64 Assembly

Caller vs Callee

Principles

When a caller calls a callee? (Control, data, memory) ?

• Control is passed to beginning of callee function
  • Once callee has executed, control is passed to…
    • caller function right after the callee function
• Data is passed to …
  • callee function via function params
• Memory is …
  • allocated when callee function starts executing
  • deallocated when callee function stops executing

Registers

Callee Saved

?

• For local data, we can use unused registers
• Must preserve values of registers before using them, then restore before control is passed back to caller function
  • How? (ex. %r13)
    • pushq %r13 (callee’s responsibility)
    • do stuff in callee function
    • popq %r13

List of callee saved ?

• rbx, r12, r13, r14, r15, rbp, rsp

Caller Saved

?

• Means that caller function must preserve values of registers before setting up callee’s arguments into the appropriate registers
• call callee
• once caller has control, restore values again

List of caller saved ?

• %r10, %r11, %rax
• paramsrdi, rsi, rdx, rcx, r8, r9

How to preserve %r10 ?

• before calling callee, pushq %r10
• call callee
• upon return, popq %r10ddd

References:

Created:: 2022-02-12 15:51

Stack

Over 6 Arguments

Procedure for when over 6 function arguments ?

• Subtract %rsp to allocate memory in stack
• mov* values onto stack
• lea* any addresses into stack if >6 or into register
• mov* values into stack if >6 or into register
• call function

Convert into assembly ?

Storage

Caller saved + Callee saved ?