什么是不结盟的访问？ （ARM /凯尔） [英] What is non-aligned access? (ARM/Keil)

问题描述

我使用的Keil编写大会ARM 7。

I'm using Keil to write Assembly for ARM 7.

我有以下运行时错误：

Non-aligned Access: ARM Instruction at 000000F8H, Memory Access at 7F7F7F7FH
Data Abort: ARM Instruction at 000000F8H, Memory Access at 7F7F7F7FH

这并不能真正帮助我，因为我不知道什么'不结盟访问'是，（较明显等，但我真的不了解的这是什么意思）我的上午的试图访问（店）为 0x7F7F7F7F ，有什么问题？

This doesn't really help me, because I don't know what 'non-aligned access' is, (other than the obvious, but I don't really understand what it means) and I am trying to access (store) to 0x7F7F7F7F, what's the issue?

搜索我只找到了几个类似的问题，无论是使用C，并解决一些非常具体到他们的code和装置，它没有涉及到这个问题。

Searching I only found a couple of similar issues, both using C, and resolved by some means very specific to their code and which didn't relate to this issue.

我做的：

LDR R0, =0x7F7F7F7F
LDR R1, LABEL
STR R1, [R0]

然后我做类似的事情有不同的标签， R0 的偏移量，但先在这里失败。

I then do a similar thing with a different label, and offsets of R0, but it fails here first.

推荐答案

的问题是，你使用的是32位（4字节）内存操作的地址必须对齐到4字节边界。这意味着地址必须是4的倍数，或者如果你preFER，地址的底部有两个位必须为零。

The issue is that the address you use for a 32-bit (4-byte) memory operation must be aligned to a 4-byte boundary. This means the address must be a multiple of 4, or if you prefer, the bottom two bits of the address must be zero.

在这种情况下，最接近的4字节对齐的地址将是 0x7F7F7F7C 或 0x7F7F7F80 。

In this case, the closest 4-byte aligned addresses would be 0x7F7F7F7C or 0x7F7F7F80.

同样， LDRH / STRH 需要2字节对齐，而<​​code> LDRB / STRB 可在任何地方工作（1字节对齐==未对齐）。

Similarly, LDRH/STRH require 2-byte alignment, whereas LDRB/STRB can operate anywhere (1-byte alignment == unaligned).

在一般的编译器/汇编需要确保你的变量是正确对齐因为他们的规模护理 - 你应该只，如果你自己生成的地址（按问题）碰上这种

In general the compiler/assembler takes care of making sure your variables are aligned correctly for the size they are - you should only run into this if you're generating addresses yourself (as per the question).

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