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

i. Prerequisite

Introduction to Organization Five ABI

2. Definition

two.1 Caller-saved registers

Caller-saved registers (AKA volatile registers, or call-clobbered) are used to hold temporary quantities that need non 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.

Information technology's normal to let a phone 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 concur long-lived values that should be preserved beyond calls.

When the caller makes a procedure call, it can expect that those registers volition hold the aforementioned value after the callee returns, making it the responsibleness of the callee to salve them and restore them before returning to the caller. Or to not touch them.

iii. Linux x86-64 part call

spec

iii.1 Callee-saved registers

r12, r13, r14, r15, rbx, rsp, rbp are the callee-saved registers - they take a "Yes" in the "Preserved across part calls" column.

3.2 Caller-saved registers

4. Example

4.1 setjmp

https://gitlab.com/kvm-unit of measurement-tests/kvm-unit-tests/-/blob/master/lib/x86/setjmp64.Southward

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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/curvation/x86/sched.Due south

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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 part call
  3. x86 Assembly Guide