写ARM汇编到文件 [英] Write to file in ARM Assembly

问题描述

我试图寄存器的整数内容写入到ARM汇编的文本文件。
我一直在读，但收效甚微 - 我从阅读技术手册，我会需要一些SWI指令推断，但我不能为我的生活找到如何做到这一点的具体实例

I'm attempting to write the integer contents of a register to a text file in ARM Assembly. I have been reading with little success - I have deduced from reading the technical manual I will require some SWI instruction, but I cannot for the life of me find a concrete example of how to do this.

操作系统是皮B型Raspbian运行。

Operating system is Raspbian running on Pi B model.

感谢您预先的任何帮助，如果您需要任何澄清，请让我知道！

Thank you in advance for any help, if you require any clarifications please let me know!

编辑：：要澄清，我组装和执行我的code成功地使用GCC。我想我的数据寄存器的值存储到一个文本文件中。

EDIT : To clarify, I am assembling and executing my code successfully using GCC. I want to store the values of my data registers to a text file.

示例：

.global main
.func main

main:
    mov r1, #19
    mov r2, #11
    add r0, r1, r2
    bx lr

在上述情况下，R0将持有的价值30.我想该值写入一个文本文件中。

In the above case, r0 would hold the value 30. I want to write that value to a text file.

推荐答案

我这样做给一个尝试，想你需要事先知道的东西。当然也有利用汇编语言编程方法很多，但我的目标毫无来自编译器和库的帮助。

I did give this a try, thinking about things you need to know beforehand. Of course there are many ways to utilize assembly programming but I aimed for no help from the compiler or libraries.

• 能够正确地使用工具链


• 链接器需要一个 _start 符号


• 定义字符串，解决这个问题


• 为 O_WRONLY ， O_CREAT 常量


• 如何连接code许可


• 找到了打开，写， FSYNC ，关闭，退出


• 如何使一个系统调用


• 某种内存管理，我用堆栈


• 指针


• ASCII再一个数字的presentation


• 寄存器加载/存储，寻址模式



• 如何调试！有趣的事情我就开始想，这应该是直截了当才发现，你需要调用硬盘的方式 FSYNC 退出进程要求内核冲厕之前。也许 O_DIRECT | O_SYNC 是一个更容易的选择。

• Be able to use toolchain correctly
• Linker expects a _start symbol
• Define a string, address it
• Constants for O_WRONLY, O_CREAT
• How to encode permission
• Find out call signatures of open, write, fsync, close, exit
• How to make a syscall
• Some kind of memory management, I used stack
• Pointers
• ASCII representation of a digit
• Load / Store of registers, addressing modes

• How to debug! Funny thing I started thinking this should be straight forward only to find out hard way that you need to call fsync before exiting the process to ask kernel for flushing. Probably O_DIRECT | O_SYNC is an easier choice.

$ as open_e.s -o open_e.o
$ ld open_e.o -o open_e
$ cat open_e.s
.global _start

_start:
@open syscall 
ldr r0, =filename
mov r1, #0101 @ O_WRONLY | O_CREAT
ldr r2, =0666 @ permissions
mov r7, #5 @ 5 is system call number for open
svc #0
cmp r0, #0
blt exit

@r0 contains fd (file descriptor, an integer)
mov r5, r0

@write syscall
@use stack as buffer
sub sp, #8 @ stack is full descending, this is how we leave some space
mov r1, #'4'
strb r1, [sp]
mov r1, #'2'
strb r1, [sp, #1]
mov r1, #'\n'
strb r1, [sp, #2]
mov r1, sp
mov r2, #3
mov r7, #4 @ 4 is write
svc #0

@fsync syscall
mov r0, r5
mov r7, #118
svc #0

@close syscall
mov r7, #6 @ 6 is close
svc #0

exit:
mov r0, #0
mov r7, #1
svc #0

.data
.align 2
filename: .asciz "out.txt"

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