汇编笔记：函数调用详细过程

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问题一：sum函数执行完毕，计算机怎么知道继续执行哪条指令？

函数运行时要在栈帧上开辟空间，esp寄存器存储的是当前函数栈顶的位置，ebp寄存器存储的是当前函数栈底的位置

首先main函数调用sum函数，第一件事是将下一条指令的地址压栈

栈帧开辟详细细节

第二件事是开辟sum函数的栈帧空间

1、push ebp 保存调用方函数的栈底地址

2、执行 mov ebp, esp 将esp赋值给ebp，此时ebp指向sum函数栈帧的栈底

栈是从高地址向低地址增长的。也就是说，当你向栈中压入新的数据时，栈顶的地址实际上是在减小。

3、执行 sub esp, 为sum函数开辟的栈帧大小 来为sum函数开辟栈帧空间

4、（可选）对栈帧初始化，比如有的vs编译器会均初始化为0xCCCCCCCC，结果是打印未初始化的int值为-858993460

栈帧回退细节

执行 mov esp, ebp

pop ebp

CPU的PC寄存器存放的是下一条指令的地址，从栈顶弹出下一条指令的地址放到CPU的PC寄存器

示例

main函数中调用sum函数

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#include <iostream>
using namespace std;

int sum(int a, int b)
{
    return a + b;
}

int main()
{
    int a = 8;
    int b = 18;

    int ret = sum(a, b);
    cout << "ret is: " << ret << endl;
    return 0;
}

执行 g++ -S calldetail.cpp

对应的汇编代码：

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	.file	"calldetail.cpp"
	.text
	.section .rdata,"dr"
_ZStL19piecewise_construct:
	.space 1
.lcomm _ZStL8__ioinit,1,1
	.text
	.globl	_Z3sumii
	.def	_Z3sumii;	.scl	2;	.type	32;	.endef
	.seh_proc	_Z3sumii
_Z3sumii:
.LFB1573:
	pushq	%rbp
	.seh_pushreg	%rbp
	movq	%rsp, %rbp
	.seh_setframe	%rbp, 0
	.seh_endprologue
	movl	%ecx, 16(%rbp)
	movl	%edx, 24(%rbp)
	movl	16(%rbp), %edx
	movl	24(%rbp), %eax
	addl	%edx, %eax
	popq	%rbp
	ret
	.seh_endproc
	.def	__main;	.scl	2;	.type	32;	.endef
	.section .rdata,"dr"
.LC0:
	.ascii "ret is: \0"
	.text
	.globl	main
	.def	main;	.scl	2;	.type	32;	.endef
	.seh_proc	main
main:
.LFB1574:
	pushq	%rbp
	.seh_pushreg	%rbp
	movq	%rsp, %rbp
	.seh_setframe	%rbp, 0
	subq	$48, %rsp
	.seh_stackalloc	48
	.seh_endprologue
	call	__main
	movl	$8, -4(%rbp)
	movl	$18, -8(%rbp)
	movl	-8(%rbp), %edx
	movl	-4(%rbp), %eax
	movl	%eax, %ecx
	call	_Z3sumii
	movl	%eax, -12(%rbp)
	leaq	.LC0(%rip), %rdx
	movq	.refptr._ZSt4cout(%rip), %rcx
	call	_ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc
	movq	%rax, %rcx
	movl	-12(%rbp), %eax
	movl	%eax, %edx
	call	_ZNSolsEi
	movq	.refptr._ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_(%rip), %rdx
	movq	%rax, %rcx
	call	_ZNSolsEPFRSoS_E
	movl	$0, %eax
	addq	$48, %rsp
	popq	%rbp
	ret
	.seh_endproc
	.def	__tcf_0;	.scl	3;	.type	32;	.endef
	.seh_proc	__tcf_0
__tcf_0:
.LFB2064:
	pushq	%rbp
	.seh_pushreg	%rbp
	movq	%rsp, %rbp
	.seh_setframe	%rbp, 0
	subq	$32, %rsp
	.seh_stackalloc	32
	.seh_endprologue
	leaq	_ZStL8__ioinit(%rip), %rcx
	call	_ZNSt8ios_base4InitD1Ev
	nop
	addq	$32, %rsp
	popq	%rbp
	ret
	.seh_endproc
	.def	_Z41__static_initialization_and_destruction_0ii;	.scl	3;	.type	32;	.endef
	.seh_proc	_Z41__static_initialization_and_destruction_0ii
_Z41__static_initialization_and_destruction_0ii:
.LFB2063:
	pushq	%rbp
	.seh_pushreg	%rbp
	movq	%rsp, %rbp
	.seh_setframe	%rbp, 0
	subq	$32, %rsp
	.seh_stackalloc	32
	.seh_endprologue
	movl	%ecx, 16(%rbp)
	movl	%edx, 24(%rbp)
	cmpl	$1, 16(%rbp)
	jne	.L8
	cmpl	$65535, 24(%rbp)
	jne	.L8
	leaq	_ZStL8__ioinit(%rip), %rcx
	call	_ZNSt8ios_base4InitC1Ev
	leaq	__tcf_0(%rip), %rcx
	call	atexit
.L8:
	nop
	addq	$32, %rsp
	popq	%rbp
	ret
	.seh_endproc
	.def	_GLOBAL__sub_I__Z3sumii;	.scl	3;	.type	32;	.endef
	.seh_proc	_GLOBAL__sub_I__Z3sumii
_GLOBAL__sub_I__Z3sumii:
.LFB2065:
	pushq	%rbp
	.seh_pushreg	%rbp
	movq	%rsp, %rbp
	.seh_setframe	%rbp, 0
	subq	$32, %rsp
	.seh_stackalloc	32
	.seh_endprologue
	movl	$65535, %edx
	movl	$1, %ecx
	call	_Z41__static_initialization_and_destruction_0ii
	nop
	addq	$32, %rsp
	popq	%rbp
	ret
	.seh_endproc
	.section	.ctors,"w"
	.align 8
	.quad	_GLOBAL__sub_I__Z3sumii
	.ident	"GCC: (x86_64-posix-seh-rev0, Built by MinGW-W64 project) 8.1.0"
	.def	_ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc;	.scl	2;	.type	32;	.endef
	.def	_ZNSolsEi;	.scl	2;	.type	32;	.endef
	.def	_ZNSolsEPFRSoS_E;	.scl	2;	.type	32;	.endef
	.def	_ZNSt8ios_base4InitD1Ev;	.scl	2;	.type	32;	.endef
	.def	_ZNSt8ios_base4InitC1Ev;	.scl	2;	.type	32;	.endef
	.def	atexit;	.scl	2;	.type	32;	.endef
	.section	.rdata$.refptr._ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_, "dr"
	.globl	.refptr._ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_
	.linkonce	discard
.refptr._ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_:
	.quad	_ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_
	.section	.rdata$.refptr._ZSt4cout, "dr"
	.globl	.refptr._ZSt4cout
	.linkonce	discard
.refptr._ZSt4cout:
	.quad	_ZSt4cout

作者：张泽中