The introduction to caller-saved registers and callee-saved registers.

1. Prerequisite

Introduction to System V ABI

2. Definition

2.1 Caller-saved registers

Caller-saved registers (AKA volatile registers, or call-clobbered) are used to hold temporary quantities that need not be preserved across calls.

For that reason, it is the caller’s responsibility to push these registers onto the stack or copy them somewhere else if it wants to restore this value after a procedure call.

It’s normal to let a call destroy temporary values in these registers, though.

2.2 Callee-saved registers

Callee-saved registers (AKA non-volatile registers, or call-preserved) are used to hold long-lived values that should be preserved across calls.

When the caller makes a procedure call, it can expect that those registers will hold the same value after the callee returns, making it the responsibility of the callee to save them and restore them before returning to the caller. Or to not touch them.

3. Linux x86-64 function call

spec

3.1 Callee-saved registers

r12, r13, r14, r15, rbx, rsp, rbp are the callee-saved registers - they have a “Yes” in the “Preserved across function calls” column.

3.2 Caller-saved registers

4. Example

4.1 setjmp

https://gitlab.com/kvm-unit-tests/kvm-unit-tests/-/blob/master/lib/x86/setjmp64.S

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.globl setjmp
setjmp:
	mov (%rsp), %rsi
	mov %rsi, (%rdi)
	mov %rsp, 0x8(%rdi)
	mov %rbp, 0x10(%rdi)
	mov %rbx, 0x18(%rdi)
	mov %r12, 0x20(%rdi)
	mov %r13, 0x28(%rdi)
	mov %r14, 0x30(%rdi)
	mov %r15, 0x38(%rdi)
	xor %eax, %eax
	ret

.globl longjmp
longjmp:
	mov %esi, %eax
	mov 0x38(%rdi), %r15
	mov 0x30(%rdi), %r14
	mov 0x28(%rdi), %r13
	mov 0x20(%rdi), %r12
	mov 0x18(%rdi), %rbx
	mov 0x10(%rdi), %rbp
	mov 0x8(%rdi), %rsp
	mov (%rdi), %rsi
	mov %rsi, (%rsp)
	ret

4.2 arch_switch_to

https://github.com/projectacrn/acrn-hypervisor/blob/release_2.7/hypervisor/arch/x86/sched.S

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    .text

   .code64
   .align       8
   .global      arch_switch_to
arch_switch_to:
	pushf
	pushq %rbx
	pushq %rbp
	pushq %r12
	pushq %r13
	pushq %r14
	pushq %r15
	pushq %rdi
	movq %rsp, (%rdi)
	movq (%rsi), %rsp
	popq %rdi
	popq %r15
	popq %r14
	popq %r13
	popq %r12
	popq %rbp
	popq %rbx
	popf
	retq

参考资料:

  1. What are callee and caller saved registers?
  2. What registers are preserved through a linux x86-64 function call
  3. x86 Assembly Guide