汇编语言实例——将小写字母转成大写字母

section .bss
    BUFFLEN equ 1024
    Buff: resb BUFFLEN

section .data

section .text

global _start

_start:
    nop

Read:
    mov eax,3
    mov ebx,0
    mov ecx,Buff
    mov edx,BUFFLEN
    int 80h
    mov esi,eax
    cmp eax,0
    je Done

    mov ecx,esi
    mov ebp,Buff
    dec ebp

Scan:
    cmp byte [ebp+ecx],61h
    jb Next
    
    cmp byte [ebp+ecx],7Ah
    ja Next

    sub byte [ebp+ecx],20h

Next:
    dec ecx
    jnz Scan

Write:
    mov eax,4
    mov ebx,1
    mov ecx,Buff
    mov edx,BUFFLEN
    int 80h
    jmp Read

Done:
    mov eax,1
    mov ebx,0
    int 80h