如何在Ubuntu中的x86_64 GAS汇编中打开和读取文件？

Question

我正在尝试复制一个从低到高的字符串程序，它将打开一个文件，运行代码并在屏幕上打印它。但我想首先尝试打开测试文件 - 没有尝试阅读用户输入内容的麻烦。

我不明白我做错了什么，第一次系统调用后％rax的值是3，我理解是错误的。

    .data

filename:
    .asciz "test.txt"

inputInFile:
    .string ""

.text
.global _start

_start:

#TO-DO: ASK FOR FILENAME

#open file syscall
mov $2,%rax
mov $filename,%rdi
mov $0,%rsi
mov $0666,%rdx
syscall


#TO-DO: ERROR FOR FILE NOT FOUND


.Loop:
#reading from file syscall, into buffer
mov $0, %rax
mov $0, %rdi
mov $inputInFile, %rsi
mov $500,%rdx
syscall
#input is in rax

#in case of end of file,  close file
cmp $0,%rax
je .exit

#append input into buffer
mov %rax,%rdx
mov $1,%rax
mov $1,%rdi
mov $inputInFile,%rsi
syscall

jmp .Loop

#close file syscall
mov $3,%rax
mov $1,%rdi
syscall


.exit:
#close file
mov $3,%rax
mov $1,%rdi
syscall

#quit
mov $60,%rax
mov $0,%rdi
syscall