Win32ASM学习[6]: PTR、OFFSET、ADDR、THIS

PTR: 指定要操作的数据尺寸

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.386
.model flat, stdcall

include    windows.inc
include    kernel32.inc
include    masm32.inc
include    debug.inc
includelib kernel32.lib
includelib masm32.lib
includelib debug.lib

.data
val db 11h, 22h, 33h, 44h, 55h, 66h, 77h, 88h

.code
main proc
    xor eax, eax                    ;清空 EAX, 同 mov eax, 0
    mov eax, dword ptr val   ;
    PrintHex eax                  ;44332211

    xor eax, eax                      ;
    mov eax, dword ptr val+1 ;
    PrintHex eax                     ;55443322

    xor eax, eax             ;
    mov ax, word ptr val     ;
    PrintHex eax             ;00002211

    xor eax, eax             ;
    mov al, byte ptr val     ;
    PrintHex eax             ;00000011
    ret
main endp
end main

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OFFSET 和 ADDR 的异同:
1、offset 不能获取局部变量的地址;
2、addr 只能用于调用函数(invoke)时, 不能用于赋值操作;
3、addr 面对局部变量时会转换为 lea 等指令, addr 面对全局变量时则直接调用 offset;
4、在 invoke 中应尽量使用 addr, 其他只用 offset.

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.386
.modelflat, stdcall

include   windows.inc
include   kernel32.inc
include   masm32.inc
include   debug.inc
includelib kernel32.lib
includelib masm32.lib
includelib debug.lib

.data
    TextAddr equ this byte ;伪指令 this 可让当前变量和下一个变量同址
    szText db'Asm', 0
.code
main proc
    PrintHex offset szText ;00403000
    PrintHex offset TextAddr ;00403000

    PrintString szText      ;Asm
    mov [TextAddr], 'a'     ;给 TextAddr 赋值
    PrintString szText      ;asm
    ret
main endp
end main