89 lines
3.4 KiB
HTML
89 lines
3.4 KiB
HTML
<html><!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
|
|
<html>
|
|
|
|
<head>
|
|
<title>80386 Programmer's Reference Manual -- Opcode LEA</title>
|
|
</head>
|
|
|
|
<body>
|
|
<b>up:</b> <a href="C17.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/C17.HTM">Chapter 17 -- 80386 Instruction Set</a><br>
|
|
<b>prev:</b><a href="LAR.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/LAR.HTM"> LAR Load Access Rights Byte</a><br>
|
|
<b>next:</b><a href="LEAVE.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/LEAVE.HTM"> LEAVE High Level Procedure Exit</a>
|
|
<p>
|
|
<hr>
|
|
<p>
|
|
<h1>LEA -- Load Effective Address</h1>
|
|
<pre>
|
|
|
|
|
|
|
|
Opcode Instruction Clocks Description
|
|
|
|
8D /r LEA r16,m 2 Store effective address for m in register r16
|
|
8D /r LEA r32,m 2 Store effective address for m in register r32
|
|
8D /r LEA r16,m 2 Store effective address for m in register r16
|
|
8D /r LEA r32,m 2 Store effective address for m in register r32
|
|
</pre>
|
|
<h2>Operation</h2>
|
|
<pre>
|
|
|
|
|
|
|
|
IF OperandSize = 16 AND AddressSize = 16
|
|
THEN r16 := Addr(m);
|
|
ELSE
|
|
IF OperandSize = 16 AND AddressSize = 32
|
|
THEN
|
|
r16 := Truncate_to_16bits(Addr(m)); (* 32-bit address *)
|
|
ELSE
|
|
IF OperandSize = 32 AND AddressSize = 16
|
|
THEN
|
|
r32 := Truncate_to_16bits(Addr(m));
|
|
ELSE
|
|
IF OperandSize = 32 AND AddressSize = 32
|
|
THEN r32 := Addr(m);
|
|
FI;
|
|
FI;
|
|
FI;
|
|
FI;
|
|
</pre>
|
|
<h2>Description</h2>
|
|
LEA calculates the effective address (offset part) and stores it in the specified register. The operand-size attribute of the instruction (represented by OperandSize in the algorithm under "Operation" above) is determined by the chosen register. The address-size attribute (represented by AddressSize) is determined by the USE attribute of the segment containing the second operand. The address-size and operand-size attributes affect the action performed by LEA, as follows:
|
|
<pre>
|
|
|
|
|
|
|
|
Operand Size Address Size Action Performed
|
|
|
|
16 16 16-bit effective address is calculated and
|
|
stored in requested 16-bit register
|
|
destination.
|
|
|
|
16 32 32-bit effective address is calculated. The
|
|
lower 16 bits of the address are stored in
|
|
the requested 16-bit register destination.
|
|
|
|
32 16 16-bit effective address is calculated. The
|
|
16-bit address is zero-extended and stored
|
|
in the requested 32-bit register destination.
|
|
|
|
32 32 32-bit effective address is calculated and
|
|
stored in the requested 32-bit register
|
|
destination.
|
|
</pre>
|
|
<h2>Flags Affected</h2>
|
|
None
|
|
<h2>Protected Mode Exceptions</h2>
|
|
#UD if the second operand is a register
|
|
<h2>Real Address Mode Exceptions</h2>
|
|
Interrupt 6 if the second operand is a register
|
|
<h2>Virtual 8086 Mode Exceptions</h2>
|
|
Same exceptions as in Real Address Mode
|
|
<p>
|
|
<hr>
|
|
<p><b>up:</b> <a href="C17.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/C17.HTM">Chapter 17 -- 80386 Instruction Set</a><br>
|
|
<b>prev:</b><a href="LAR.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/LAR.HTM"> LAR Load Access Rights Byte</a><br>
|
|
<b>next:</b><a href="LEAVE.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/LEAVE.HTM"> LEAVE High Level Procedure Exit</a>
|
|
</body>
|
|
|