?? csdn_文檔中心_屏幕取詞核心內幕.htm
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<P class=MsoNormal style="MARGIN-LEFT: 18pt"><SPAN lang=EN-US><SPAN
style="mso-tab-count: 2">
</SPAN>mov sp, offset stack;<SPAN
style="mso-tab-count: 1">
</SPAN></SPAN><SPAN lang=EN-US
style="FONT-SIZE: 9pt; mso-bidi-font-size: 10.0pt">/* </SPAN><SPAN
style="FONT-FAMILY: 宋體; FONT-SIZE: 9pt; mso-ascii-font-family: Arial; mso-bidi-font-size: 10.0pt">設置</SPAN><SPAN
lang=EN-US
style="FONT-SIZE: 9pt; mso-bidi-font-size: 10.0pt">16</SPAN><SPAN
style="FONT-FAMILY: 宋體; FONT-SIZE: 9pt; mso-ascii-font-family: Arial; mso-bidi-font-size: 10.0pt">位堆棧指針</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 9pt; mso-bidi-font-size: 10.0pt">
*/</SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 18pt"><SPAN lang=EN-US><SPAN
style="mso-tab-count: 2">
</SPAN>add sp, 8192;<SPAN style="mso-tab-count: 1">
</SPAN></SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 18pt"><SPAN
lang=EN-US>}</SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 18pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt; mso-bidi-font-size: 10.0pt">/* </SPAN><SPAN
style="FONT-FAMILY: 宋體; FONT-SIZE: 9pt; mso-ascii-font-family: Arial; mso-bidi-font-size: 10.0pt">此處加入</SPAN><SPAN
lang=EN-US
style="FONT-SIZE: 9pt; mso-bidi-font-size: 10.0pt">16</SPAN><SPAN
style="FONT-FAMILY: 宋體; FONT-SIZE: 9pt; mso-ascii-font-family: Arial; mso-bidi-font-size: 10.0pt">位代碼要實現的功能</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 9pt; mso-bidi-font-size: 10.0pt">
*/</SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 18pt"><SPAN
lang=EN-US>_asm{</SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 18pt"><SPAN lang=EN-US><SPAN
style="mso-tab-count: 2">
</SPAN>mov ss, prev_seg;</SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 18pt"><SPAN lang=EN-US><SPAN
style="mso-tab-count: 2">
</SPAN>mov esp, dword ptr prev_ofs;<SPAN style="mso-tab-count: 1">
</SPAN></SPAN><SPAN lang=EN-US
style="FONT-SIZE: 9pt; mso-bidi-font-size: 10.0pt">/* </SPAN><SPAN
style="FONT-FAMILY: 宋體; FONT-SIZE: 9pt; mso-ascii-font-family: Arial; mso-bidi-font-size: 10.0pt">恢復</SPAN><SPAN
lang=EN-US
style="FONT-SIZE: 9pt; mso-bidi-font-size: 10.0pt">32</SPAN><SPAN
style="FONT-FAMILY: 宋體; FONT-SIZE: 9pt; mso-ascii-font-family: Arial; mso-bidi-font-size: 10.0pt">位堆棧指針</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 9pt; mso-bidi-font-size: 10.0pt">
*/</SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 18pt"><SPAN lang=EN-US><SPAN
style="mso-tab-count: 2">
</SPAN>mov ds, prev_ds;</SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 18pt"><SPAN lang=EN-US><SPAN
style="mso-tab-count: 2">
</SPAN>lea sp, word ptr [bp-2];</SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 18pt"><SPAN lang=EN-US><SPAN
style="mso-spacerun: yes"> </SPAN><SPAN
style="mso-tab-count: 1"> </SPAN>pop
ds;</SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 18pt"><SPAN lang=EN-US><SPAN
style="mso-tab-count: 2">
</SPAN>pop<SPAN style="mso-tab-count: 1"> </SPAN>bp;</SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 18pt"><SPAN lang=EN-US><SPAN
style="mso-spacerun: yes"> </SPAN>dec
bp;</SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 18pt"><SPAN lang=EN-US><SPAN
style="mso-tab-count: 2">
</SPAN>db 66h;</SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 18pt"><SPAN lang=EN-US><SPAN
style="mso-tab-count: 2">
</SPAN>retf;</SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 18pt"><SPAN
lang=EN-US>}</SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 18pt"><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">由于調用中傳遞的參數有限，所以涉及的代碼并不多，唯一比較復雜之處在</SPAN><SPAN
lang=EN-US>16</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位側，它臨時轉向一個</SPAN><SPAN
lang=EN-US>16</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位堆棧，服務于來自</SPAN><SPAN
lang=EN-US>32</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位的調用者的請求。在</SPAN><SPAN
lang=EN-US>16</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位側入口處，必須存放好</SPAN><SPAN
lang=EN-US>32</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位調用者的</SPAN><SPAN
lang=EN-US>32</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位堆棧的指針，并且在</SPAN><SPAN
lang=EN-US>16</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位側返回時恢復它。由代碼可見，這個過程是不可重入的，即一次只支持一個調用者，由于調用者只有</SPAN><SPAN
lang=EN-US>LTW32</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">的</SPAN><SPAN
lang=EN-US>32</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位側代碼，所以此限制可以滿足。另外，在</SPAN><SPAN
lang=EN-US>16</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位代碼返回時，必須恢復</SPAN><SPAN
lang=EN-US>32</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位調用者的</SPAN><SPAN
lang=EN-US>48</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位堆棧指針（</SPAN><SPAN
lang=EN-US>SS:ESP</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">）而不是</SPAN><SPAN
lang=EN-US>32</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位的</SPAN><SPAN
lang=EN-US>CS:SP</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">，而且必須用一個</SPAN><SPAN
lang=EN-US>48</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位地址（</SPAN><SPAN
lang=EN-US>16:32</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">）遠返回（</SPAN><SPAN
lang=EN-US>66h RETF</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">）到它的</SPAN><SPAN
lang=EN-US>32</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位調用者。</SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 18pt"><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">處理好這些細節，實現</SPAN><SPAN
lang=EN-US>32</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位到</SPAN><SPAN
lang=EN-US>16</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位的形式替換實際上是很簡單的。</SPAN></P>
<P class=MsoNormal
style="MARGIN-LEFT: 18pt; TEXT-INDENT: -18pt; mso-list: l31 level1 lfo7; tab-stops: list 18.0pt"><SPAN
lang=EN-US
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-fareast-font-family: 黑體">2．<SPAN
style="FONT: 7pt 'Times New Roman'"> </SPAN></SPAN><SPAN
lang=EN-US
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-fareast-font-family: 黑體">32</SPAN><SPAN
style="FONT-FAMILY: 黑體; FONT-SIZE: 12pt; mso-ascii-font-family: Arial; mso-bidi-font-size: 10.0pt">位代碼與</SPAN><SPAN
lang=EN-US
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-fareast-font-family: 黑體">16</SPAN><SPAN
style="FONT-FAMILY: 黑體; FONT-SIZE: 12pt; mso-ascii-font-family: Arial; mso-bidi-font-size: 10.0pt">位代碼的數據交換</SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 18pt"><SPAN
lang=EN-US>32</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位代碼使用</SPAN><SPAN
lang=EN-US>16</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位段地址加</SPAN><SPAN
lang=EN-US>32</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位線性地址（</SPAN><SPAN
lang=EN-US>16:32</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">）的地址形式，</SPAN><SPAN
lang=EN-US>16</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位代碼使用</SPAN><SPAN
lang=EN-US>16</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位段選擇符（</SPAN><SPAN
lang=EN-US>selector</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">）加</SPAN><SPAN
lang=EN-US>16</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位偏移（</SPAN><SPAN
lang=EN-US>16:16</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">）的地址形式。在</SPAN><SPAN
lang=EN-US>Windows 95</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">的</SPAN><SPAN
lang=EN-US>32</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位側，段址</SPAN><SPAN
lang=EN-US>28h</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">是系統段，即通過</SPAN><SPAN
lang=EN-US>CS=28h</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">或</SPAN><SPAN
lang=EN-US>DS=28h</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">可以訪問系統的</SPAN><SPAN
lang=EN-US>4G</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">空間，其它應用程序的地址空間都是映射到</SPAN><SPAN
lang=EN-US>28h</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">段的</SPAN><SPAN
lang=EN-US>4G</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">空間中。</SPAN><SPAN
lang=EN-US>Windows95</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">中所有</SPAN><SPAN
lang=EN-US>32</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位進程的地址空間（共</SPAN><SPAN
lang=EN-US>4G</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">）的高</SPAN><SPAN
lang=EN-US>2G</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">（</SPAN><SPAN
lang=EN-US>80000000H~FFFFFFFFH</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">）全部映射到</SPAN><SPAN
lang=EN-US>28:80000000~28:FFFFFFFFH</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">。即這塊區域是所有</SPAN><SPAN
lang=EN-US>32</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位程序共享的。這里一般存放系統</SPAN><SPAN
lang=EN-US>DLL</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">、虛擬設備驅動程序（</SPAN><SPAN
lang=EN-US>VxD</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">）、內存映射文件、</SPAN><SPAN
lang=EN-US>16</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位應用程序和</SPAN><SPAN
lang=EN-US>16</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位全局堆等。最后一項很重要，這為</SPAN><SPAN
lang=EN-US>32</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位代碼與</SPAN><SPAN
lang=EN-US>16</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位代碼交換數據提供了一個簡便的方法。因為</SPAN><SPAN
lang=EN-US>16</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位程序的段選擇符的基址即是其所映射的系統段中的線性地址，這樣，只要能夠得到這個線性地址，</SPAN><SPAN
lang=EN-US>32</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位代碼就可以輕易地訪問到</SPAN><SPAN
lang=EN-US>16</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位程序的數據（</SPAN><SPAN
lang=EN-US>LTW32 </SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">的</SPAN><SPAN
lang=EN-US>32</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位側使用此方法從</SPAN><SPAN
lang=EN-US>16</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位側獲得屏幕截獲的信息）。而</SPAN><SPAN
lang=EN-US>16</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">位段選擇符的線性基址可以通過使用系統調用</SPAN><SPAN
lang=EN-US>GetSelectorBase()</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Arial">得到，具體實現可參考源程序。線性地址計算的例子如下：</SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 42.5pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt; mso-bidi-font-size: 10.0pt">16</SPAN><SPAN
style="FONT-FAMILY: 宋體; FONT-SIZE: 9pt; mso-ascii-font-family: Arial; mso-bidi-font-size: 10.0pt">位地址：</SPAN><SPAN
lang=EN-US
style="FONT-SIZE: 9pt; mso-bidi-font-size: 10.0pt">07F2:1234H</SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 42.5pt"><SPAN
style="FONT-FAMILY: 宋體; FONT-SIZE: 9pt; mso-ascii-font-family: Arial; mso-bidi-font-size: 10.0pt">段選擇符</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 9pt; mso-bidi-font-size: 10.0pt"><SPAN
style="mso-tab-count: 1">
</SPAN>07F2H</SPAN><SPAN
style="FONT-FAMILY: 宋體; FONT-SIZE: 9pt; mso-ascii-font-family: Arial; mso-bidi-font-size: 10.0pt">的線性基址為：</SPAN><SPAN
lang=EN-US
style="FONT-SIZE: 9pt; mso-bidi-font-size: 10.0pt">82F41300H</SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 42.5pt"><SPAN
style="FONT-FAMILY: 宋體; FONT-SIZE: 9pt; mso-ascii-font-family: Arial; mso-bidi-font-size: 10.0pt">段選擇符</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 9pt; mso-bidi-font-size: 10.0pt"><SPAN
style="mso-tab-count: 1">
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