Intel x86 到 ARM 程序集转换 [英] Intel x86 to ARM assembly conversion
问题描述
我目前正在学习ARM汇编语言；
I am currently learning ARM assembly language;
为此，我正在尝试将一些 x86 代码(AT&T 语法) 转换为 ARM 汇编 (Intel 语法) 代码.
To do so, I am trying to convert some x86 code (AT&T Syntax) to ARM assembly (Intel Syntax) code.
__asm__("movl $0x0804c000, %eax;");
__asm__("mov R0,#0x0804c000");
从这个 document，我了解到在 x86 中的 Chunk 1堆结构从 0x0804c000 开始.但是当我尝试在 arm 中做同样的事情时，我收到以下错误:
From this document, I learn that in x86 the Chunk 1 of the heap structure starts from 0x0804c000. But I when I try do the same in arm,
I get the following error:
/tmp/ccfNZp9F.s:174: Error: invalid constant (804c000) after fixup
我假设问题是 ARM 只能加载 32bit 说明.
I am assuming the problem is that ARM can only load 32bit instructions.
Question 1: Any idea what would be the first chunk in case of ARM processors?
Question 2:
从我之前的问题，我知道了内存间接寻址的工作原理.
From my previous question, I know how memory indirect addressing works.
下面写的片段是否做同样的工作?
Are the snippets written below doing the same job?
movl (%eax), %ebx
LDR R0,[R1]
我正在使用 ARMv7 Processor rev 4 (v7l)
推荐答案
问题一解答
ARM 上的 MOV 指令只有 12 位可用于立即数，而这些位是这样使用的:8 位用于值，4 位用于指定向右的旋转次数(旋转次数相乘)2，以增加范围).
The MOV instruction on ARM only has 12 bits available for an immediate value, and those bits are used this way: 8 bits for value, and 4 bits to specify the number of rotations to the right (the number of rotations is multiplied by 2, to increase the range).
这意味着该指令只能使用有限数量的值.它们是:
This means that only a limited number of values can be used with that instruction. They are:
- 0-255
- 256、260、264、...、1020
- 1024、1040、1056、...、4080
- 等
等等.您收到该错误是因为无法使用 8 位 + 旋转创建常量.您可以按照以下指令将该值加载到寄存器中:
And so on. You are getting that error because your constant can't be created using the 8 bits + rotations. You can load that value onto the register following instruction:
LDR r0, =0x0804c000
请注意，这是一条伪指令.汇编器基本上会将该常量放在代码中的某个位置，并将其作为内存位置加载，并与 PC(程序计数器)有一些偏移.
Notice that this is a pseudo-instruction though. The assembler will basically put that constant somewhere in your code and load it as a memory location with some offset to the PC (program counter).
问题 2 的答案
是的，这些说明是等效的.
Yes those instructions are equivalent.
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