问题描述
我想问一下,为什么它是确定这样写的:
I would like to ask why it is ok to write something like this:
.section .data
hello:
.ascii "Hello World\n"
.equ lenhello, . - hello
但它是不正确的,当我键入:
but it is not right when i type:
.section .data
hello:
.ascii "Hello World\n"
lenhello:
.long . - hello
在调用后SYS_WRITE函数首先code正常工作,但除了编写的Hello World第二个产生了很多垃圾
After calling sys_write function first code works fine, but the second one apart from writing hello world produces a lot of trash
推荐答案
您忘了告诉你如何使用的值。如果你这样做 MOVL lenhello,EDX%
它应该工作的罚款。我假设你做了 MOVL $ lenhello,EDX%
代替。
You have forgotten to show how you use the value. If you do movl lenhello, %edx
it should work fine. I assume you did movl $lenhello, %edx
instead.
的 .EQU
指令定义一个符号,其价值将是长度,所以你会引用为 $ lenhello
。它不保留任何内存。用你的第二个版本,您可以定义在内存中包含长度可变的。 $ lenhello
在这种情况下将是你的变量的地址,而不是长度。
The .equ
directive defines a symbol whose value will be the length, so you will reference that as $lenhello
. It doesn't reserve any memory. Using your second version, you define a variable in memory that contains the length. $lenhello
in that case will be the address of your variable, and not the length.
全部样本code:
.section .data
hello:
.ascii "Hello World\n"
lenhello:
.long . - hello
.text
.globl _start
_start:
movl $1, %ebx
movl $hello, %ecx
movl lenhello, %edx
movl $4, %eax
int $0x80
movl $1, %eax
movl $0, %ebx
int $0x80
这无关与。
符号。
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