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Retidy, removing align=left from headings and empty paragraphs

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James Gregory 2013-12-30 15:37:13 +11:00
commit a96a114403
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@ -1,5 +1,4 @@
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
@ -19,17 +18,21 @@
<center>
<table border="1">
<tr>
<td><a href="11-07.html">Previous</a></td>
<td>
<a href="11-07.html">Previous</a>
</td>
<td><a href="index.html">Table of Contents</a></td>
<td>
<a href="index.html">Table of Contents</a>
</td>
<td><a href="12-01.html">Next</a></td>
<td>
<a href="12-01.html">Next</a>
</td>
</tr>
</table>
</center>
<p><br /></p>
<p>Well, there&rsquo;s only one instruction other than <b>POPF</b> that loads the FLAGS register directly from the stack, and that&rsquo;s <b>IRET</b>, which loads the FLAGS register from the stack as it branches, as shown in Figure 11.5. iret has no known bugs of the sort that plague <b>POPF</b>, so it&rsquo;s certainly a candidate to replace popf in non-interruptible applications. Unfortunately, <b>IRET</b> loads the FLAGS register with the <i>third</i> word down on the stack, not the word on top of the stack, as is the case with <b>POPF</b>; the far return address that <b>IRET</b> pops into CS:IP lies between the top of the stack and the word popped into the FLAGS register.</p>
<p>Obviously, the segment:offset that <b>IRET</b> expects to find on the stack above the pushed flags isn&rsquo;t present when the stack is set up for <b>POPF</b>, so we&rsquo;ll have to adjust the stack a bit before we can substitute <b>IRET</b> for <b>POPF</b>. What we&rsquo;ll have to do is push the segment:offset of the instruction after our workaround code onto the stack right above the pushed flags. <b>IRET</b> will then branch to that address and pop the flags, ending up at the instruction after the workaround code with the flags popped. That&rsquo;s just the result that would have occurred had we executed <b>POPF</b>&mdash;WITH the bonus that no interrupts can accidentally occur when the Interrupt flag is 0 both before and after the pop.</p>
@ -103,16 +106,20 @@ EMULATE_POPFmacro
<p>And now you know the nature of and the workaround for the <b>POPF</b> bug. Whether you ever need the workaround or not, it&rsquo;s a neatly packaged example of the tremendous flexibility of the x86 instruction set.</p>
<p><br /></p>
<center>
<table border="1">
<tr>
<td><a href="11-07.html">Previous</a></td>
<td>
<a href="11-07.html">Previous</a>
</td>
<td><a href="index.html">Table of Contents</a></td>
<td>
<a href="index.html">Table of Contents</a>
</td>
<td><a href="12-01.html">Next</a></td>
<td>
<a href="12-01.html">Next</a>
</td>
</tr>
</table>
</center>