英文:
Writing two strings to console not working
问题
这是您期望的输出：
0000
1111
您之前的代码有一些问题。在第二个字符串输出之后，您没有添加换行符 (0xA)，这导致输出没有分行。此外，您的长度变量 len 和 otherLen 应该是 dd 类型而不是 db 类型，以确保它们被正确地加载为 32 位整数。以下是已经更正的代码：
section .data
str: db "0000", 0xA
len: dd 5
otherStr: db "1111", 0xA
otherLen: dd 5
global _start
section .text
_start:
; system call to print the first string
mov eax, 4 ; "write" system call
mov ebx, 1 ; Indicates to write to standard out
mov ecx, str ; The string
mov edx, [len] ; The length of the string
int 0x80
; system call to print the second string
mov eax, 4 ; "write" system call
mov ebx, 1 ; Indicates to write to standard out
mov ecx, otherStr ; The string
mov edx, [otherLen] ; The length of the string
int 0x80
; exit the program
mov eax, 1
mov ebx, 0
int 0x80
请注意，我更正了长度变量的类型，以确保它们以正确的方式加载。希望这次的代码会输出您期望的结果。使用与您之前相同的汇编和链接命令进行编译和运行。
英文:
I’m new to x_86 assembly language, and trying write some simple stuff to the console.
When I try this:
section .data
str: db "0000", 0xA
len: db 5
global _start
section .text
_start:
; system call to print the string
mov eax, 4 ; "write" system call
mov ebx, 1 ; Indicates to write to standard out
mov ecx, str ; The string
mov edx, [len] ; The length of the string
int 0x80
; exit the program
mov eax, 1
mov ebx, 0
int 0x80
It works fine, and prints out “0000”. But if I then try this:
section .data
str: db "0000", 0xA
len: db 5
otherStr: db "1111", 0xA
otherLen: db 5
global _start
section .text
_start:
; system call to print the string
mov eax, 4 ; "write" system call
mov ebx, 1 ; Indicates to write to standard out
mov ecx, str ; The string
mov edx, [len] ; The length of the string
int 0x80
; system call to print the string
mov eax, 4 ; "write" system call
mov ebx, 1 ; Indicates to write to standard out
mov ecx, otherStr ; The string
mov edx, [otherLen] ; The length of the string
int 0x80
; exit the program
mov eax, 1
mov ebx, 0
int 0x80
It outputs all this gobblygook:
0000
1111
(#
/
6
sha.asmstrlenotherStrotherLen__bss_start_edata_end.symtab.strtab.shstrtab.text.dat:!
;!'1111
The output I’m expecting is just:
0000
1111
What am I doing wrong here? This is on Fedora Linux and using the NASM assembler. The commands I’m using to link and assemble are these:
nasm -f elf32 example.asm -o ex1.o
ld -m elf_i386 ex1.o -o ex1
答案1
得分: 3
len 的定义如下：
len: db 5
单独来看，这没问题。
它的加载方式如下：
mov edx, [len]
单独来看，这也没问题。
但是放在一起就有问题了。加载操作加载了一个DWORD，而变量只有一个字节的空间，因此加载了3个额外的字节，这些字节是"something else"。在第一个程序中，它们是用于填充数据段到页面大小的倍数的“零填充”的零。在第二个程序中，它们不是零。
你可以将长度（两者都是）改为DWORD（例如len: dd 5），或者使用零扩展来加载，例如movzx edx, byte [len]。
英文:
len is defined like this
len: db 5
By itself that's fine.
It's loaded like this:
mov edx, [len]
By itself that's also fine.
But together they're wrong. The load loads a DWORD, and there's only one byte dedicated to the variable, so 3 extra bytes are loaded that are "something else". In the first program, they're zeroes from the "zero fill" to pad out the data section to a multiple of the page size. In the second program, they're not zero.
You could make the lengths (both of them) DWORD (eg len: dd 5) or load them with zero-extension eg movzx edx, byte [len].
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