组装:我的线性搜索代码有问题

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【中文标题】组装:我的线性搜索代码有问题【英文标题】:Assembly: troubles with my linear search code 【发布时间】:2017-04-03 02:09:55 【问题描述】:

对于分配,我必须完成程序的代码,该程序使用循环将每个数组元素与通过用户输入提供的目标值进行比较。例如,当程序要求我输入一个数字并且我输入数字 6 时,它应该给我这个列表中的第六个数字。 '7','3','2','1','0','5','6','4','8','9'

我输入了 cmets 让我输入的内容,但是当我尝试编译它时,我不断收到此错误。

main.o: In function `getNextElement':
main.asm:(.text+0x92): relocation truncated to fit: R_386_8 against '.data' 

谁能告诉我我在这里做错了什么?

    ;;;;;;;;;;;;;;;;;;;;    MACRO DEFINITIONS   ;;;;;;;;;;;;;;;;;;;;
; A macro with two parameters
; Implements the write system call
    %macro writestring 2
        mov eax, 4  ;sys_write system call number
        mov ebx, 1  ;file descriptor std_out
        mov ecx, %1 ;message to write from parameter 1
        mov edx, %2 ;message length from parameter 2
        int 0x80
    %endmacro
; A macro with two parameters
; Implements the sys_read call
    %macro read_string 2
        mov eax, 3  ;sys_write system call number
        mov ebx, 2  ;file descriptor std_in
        mov ecx, %1 ;variable/array to hold data, pass by reference in param 1
        mov edx, %2 ;number of bytes to read passed by value in param 2
        int 0x80
    %endmacro

;;;;;;;;;;;;;;;;;;;;    DATA SEGMENT    ;;;;;;;;;;;;;;;;;;;;
section .data
msg1 db 'Here are the elements: '
lenmsg1 equ $-msg1
msg2 db 'Enter a number to search for: '
lenmsg2 equ $-msg2
msg3 db 'The target value was found at index '
lenmsg3 equ $-msg3
msg4 db 'The target value was NOT found...',0x0a, 0x0d
lenmsg4 equ $-msg4
asciinums db '7','3','2','1','0','5','6','4','8','9'
lenasciinums equ $-asciinums
crlf db 0x0d, 0x0a
lencrlf equ $ - crlf                
target db 0x00
targetlocation db 0x30

section .text
    global _start
_start:
    writestring msg1, lenmsg1
    writestring asciinums, lenasciinums
    writestring crlf, lencrlf
    writestring msg2, lenmsg2
    read_string target, 1
    writestring crlf, lencrlf
    mov eax, asciinums  ;eax holds base address
    mov ecx, 0          ;ecx is index register
getNextElement:
    mov [eax+ecx], al   ;copy value from asciinums into an 8-bit register
    cmp al, target      ;compare the 8-bit register to target value
    je  targetlocation  ;jump if equal to the found label
    inc ecx             ;increment index register
    cmp ecx, 10         ;compare index register to decimal 10
    jne getNextElement  ;if index register not equal to 10 go to getNextElement

    writestring msg4, lenmsg4
    jmp terminate
found:
    add [targetlocation], ecx
    writestring msg3, lenmsg3
    writestring targetlocation, 1
    writestring crlf, lencrlf
terminate:
    mov eax, 1          ;terminate program
    int 0x80

我也知道问题出在这部分代码。

    mov eax, asciinums  ;eax holds base address
    mov ecx, 0          ;ecx is index register
getNextElement:
    mov [eax+ecx], al   ;copy value from asciinums into an 8-bit register
    cmp al, target      ;compare the 8-bit register to target value
    je  targetlocation  ;jump if equal to the found label
    inc ecx             ;increment index register
    cmp ecx, 10         ;compare index register to decimal 10
    jne getNextElement  ;if index register not equal to 10 go to getNextElement

这是我用来编译的网站。任何帮助将不胜感激。

https://www.tutorialspoint.com/compile_assembly_online.php

【问题讨论】:

cmp al, target 将目标地址与 AL 进行比较。您想比较target 的内容,所以它应该是cmp al, [target]。此错误会导致您收到的链接器错误。同样,我认为您的意思不是je targetlocation(这是数据部分中的标签)。也许你的意思是je found? (这就是评论所暗示的) @MichaelPetch 它可以工作,但最初当我将目标位置更改为“je found”时,输出告诉我“找不到目标值”。将其更改为“找到 jmp”,但这只是说“在索引 0 处找到目标值”。任何想法如何解决这一问题?我尝试了不同的跳跃功能,但它们没有给我想要的。 【参考方案1】:

假设您正在为 x86 架构编写代码,问题是 getNextElement 中的 je 指令。 je 指令是短跳转,它只需要相对地址作为参数,不能用于间接跳转。这里可以看看jejmp指令的区别:

http://x86.renejeschke.de/html/file_module_x86_id_146.html

http://x86.renejeschke.de/html/file_module_x86_id_147.html

添加:

mov [eax+ecx], al ;copy value from asciinums into an 8-bit register

在这里,您将al 移动到内存中,而评论则相反。修复它,使用je found 并重试。

添加:

还有一个: mov [eax+ecx], al ;copy value from asciinums into an 8-bit register 在这里,您通过将数据加载到al 来破坏eax 注册。在下一个循环中,您将从内存中获取垃圾。

检查,在修复所有提到的错误后,它可以完美运行。

;;;;;;;;;;;;;;;;;;;;    MACRO DEFINITIONS   ;;;;;;;;;;;;;;;;;;;;
; A macro with two parameters
; Implements the write system call
    %macro writestring 2
        mov eax, 4  ;sys_write system call number
        mov ebx, 1  ;file descriptor std_out
        mov ecx, %1 ;message to write from parameter 1
        mov edx, %2 ;message length from parameter 2
        int 0x80
    %endmacro
; A macro with two parameters
; Implements the sys_read call
    %macro read_string 2
        mov eax, 3  ;sys_write system call number
        mov ebx, 2  ;file descriptor std_in
        mov ecx, %1 ;variable/array to hold data, pass by reference in param 1
        mov edx, %2 ;number of bytes to read passed by value in param 2
        int 0x80
    %endmacro

;;;;;;;;;;;;;;;;;;;;    DATA SEGMENT    ;;;;;;;;;;;;;;;;;;;;
section .data
msg1 db 'Here are the elements: '
lenmsg1 equ $-msg1
msg2 db 'Enter a number to search for: '
lenmsg2 equ $-msg2
msg3 db 'The target value was found at index '
lenmsg3 equ $-msg3
msg4 db 'The target value was NOT found...',0x0a, 0x0d
lenmsg4 equ $-msg4
asciinums db '7','3','2','1','0','5','6','4','8','9'
lenasciinums equ $-asciinums
crlf db 0x0d, 0x0a
lencrlf equ $ - crlf                
target db 0x00
targetlocation db 0x30

section .text
    global _start
_start:
    writestring msg1, lenmsg1
    writestring asciinums, lenasciinums
    writestring crlf, lencrlf
    writestring msg2, lenmsg2
    read_string target, 1
    writestring crlf, lencrlf
    mov eax, asciinums  ;eax holds base address
    mov ecx, 0          ;ecx is index register
getNextElement:
    mov bl, [eax+ecx]   ;copy value from asciinums into an 8-bit register
    cmp bl, [target]    ;compare the 8-bit register to target value
    je  found           ;jump if equal to the found label
    inc ecx             ;increment index register
    cmp ecx, 10         ;compare index register to decimal 10
    jne getNextElement  ;if index register not equal to 10 go to getNextElement

    writestring msg4, lenmsg4
    jmp terminate
found:
    add [targetlocation], ecx
    writestring msg3, lenmsg3
    writestring targetlocation, 1
    writestring crlf, lencrlf
terminate:
    mov eax, 1          ;terminate program
    int 0x80

【讨论】:

是的,如果评论有帮助,请不要忘记投票。

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