我尝试从scanf获得3个输入后将结果输出给用户。
当我运行我的代码时，我能够获得所需的输入。然而，在我收集输入并开始计算后它会崩溃。
顺便说一句，我使用的是带有g ++和NASM 64bit的Ubuntu 14.04。
以下是应该的样子：
This program is brought to you by Chris Tarazi
Welcome to Areas of Trapezoids
Please enter one of the base numbers: 5.8
Please enter the other base number: 2.2
Please enter the height: 6.5
****//Crashes here with Segmentation fault (core dumped)****
The area of a trapezoid with sizes 5.799999999999999365, 2.200000000000000153,
and 6.500000000000000000 is 26.000000000000000328
Have a nice day. Enjoy your trapezoids.
C++档案：
#include <stdio.h>
#include <stdint.h>
extern "C" double ComputeArea(); // links with global in assembly
using namespace std;
int main()
{
double area;
printf("This program is brought to you by Chris Tarazi.\n");
area = ComputeArea();
printf("Have a nice day. Enjoy your trapezoids.\n");
return 0;
}
装配文件：
extern printf ; This function will be linked later.
extern scanf
global ComputeArea ; Declare function global to link with "extern" from C++.
;---------------------------------Declare variables-------------------------------------------
segment .data
welcome: db "Welcome to the area of trapezoids.", 10, 0
input: db "Please enter one of the base numbers: ", 0
secInput: db "Please enter the other base number: ", 0
output: db "The area of a trapezoid with sizes %1.18lf, %1.18lf, and %1.18lf is %1.18lf .", 10, 0
hInput: db "Please enter the height: ", 0
inputformat: db "%lf", 0
stringformat: db "%s", 0
fourfloatformat: db "%1.18lf %1.18lf %1.18lf %1.18lf", 0
;---------------------------------Begin segment of executable code------------------------------
segment .text
ComputeArea: ; Area of trapezoid = ((a + b) / 2) * h.
push rbp ; Save a copy of the stack base pointer
mov rbp, rsp ; We do this in order to be 100% compatible with C and C++.
push rbx ; Back up rbx
push rcx ; Back up rcx
push rdx ; Back up rdx
push rsi ; Back up rsi
push rdi ; Back up rdi
push r8 ; Back up r8
push r9 ; Back up r9
push r10 ; Back up r10
push r11 ; Back up r11
push r12 ; Back up r12
push r13 ; Back up r13
push r14 ; Back up r14
push r15 ; Back up r15
pushf ; Back up rflags
;---------------------------------Output messages to user---------------------------------------
mov qword rax, 0
mov rdi, stringformat
mov rsi, welcome
call printf
mov qword rax, 0
mov rdi, stringformat
mov rsi, input
call printf
push qword 0
mov qword rax, 0
mov rdi, inputformat
mov rsi, rsp ;firstbase
call scanf
movsd xmm0, [rsp]
pop rax
mov qword rax, 0
mov rdi, stringformat
mov rsi, secInput
call printf
push qword 0
mov qword rax, 0
mov rdi, inputformat
mov rsi, rsp ;secondbase
call scanf
movsd xmm1, [rsp + 4]
pop rax
mov qword rax, 0
mov rdi, stringformat
mov rsi, hInput
call printf
push qword 0
mov qword rax, 0
mov rdi, inputformat
mov rsi, rsp ;height
call scanf
movsd xmm2, [rsp + 8]
pop rax
;---------------------------------Begin ComputeArea Calculation-----------------------------------
mov rax, 2
cvtsi2sd xmm3, rax
addsd xmm0, xmm1
divsd xmm0, xmm3
mulsd xmm0, xmm2
ret
;---------------------------------Output result to user-------------------------------------------
mov rax, 3
mov rdi, output
call printf
答案 0 :(得分：1)
首先，为什么你要保存那些寄存器的全部？！？ 64位Linux的ABI表示，如果在函数中使用这些寄存器，则只需要保存rbx，rbp和r12 - r15。另外，你使用Assembler，不需要在64bit的地方创建一个堆栈帧（加上你甚至不使用rbp！所以为什么要创建一个堆栈帧？）唯一非常重要的是为确保您的堆栈在16字节边界上对齐 - 调用将推送一个8字节的返回地址，因此您的ComputeArea函数所需要的只是sub rsp, 8和add rsp, 8。
在您使用scanf的第一个rsp中，如果没有调整它，您只是覆盖了一些内容！
你在这里做一些计算：
mov rax, 2
cvtsi2sd xmm3, rax
addsd xmm0, xmm1
divsd xmm0, xmm3
mulsd xmm0, xmm2
ret
你从这里的程序返回，但不要弹出你刚刚推送的所有寄存器!!所以基本上你的堆栈指针都搞砸了！ CPU不知道返回地址是什么！
你在序言中所做的事情，必须在你回来之前在结语中逆转！
也许，你应该开始简单，阅读3个花车并尝试打印它们！
当我更正你的代码时，这是我的输出：
Welcome to the area of trapezoids.
Please enter one of the base numbers: 5.8
Please enter the other base number: 2.2
Please enter the height: 6.5
The area of a trapezoid with sizes 5.799999999999999822, 2.200000000000000178, and 6.500000000000000000 is 26.000000000000000000 .