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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Debugging Information Extension for Objective C Properties</title>
<link rel="stylesheet" href="llvm.css" type="text/css">
</head>
<body>
<h1>
Debugging Information Extension for Objective C Properties
</h1>
<ol>
<li><a href="#introduction">Introduction</a></li>
<li><a href="#proposal">Proposal</a></li>
<li><a href="#newattributes">New DWARF Attributes</a></li>
<li><a href="#newconstants">New DWARF Constants</a></li>
</ol>
<div class="doc_author">
<p>Written by Jim Ingham and Devang Patel </p>
</div>
<!-- *********************************************************************** -->
<h2>
<a name="introduction">Introduction</a>
</h2>
<!-- *********************************************************************** -->
<div>
<p>Objective C provides a simpler way to declare and define accessor methods
using declared properties. The language provides features to declare a
property and to let compiler synthesize accessor methods.
</p>
<p>The debugger lets developer inspect Objective C interfaces and their
instance variables and class variables. However, the debugger does not know
anything about the properties defined in Objective C interfaces. The debugger
consumes information generated by compiler in DWARF format. The format does
not support encoding of Objective C properties. This proposal describes DWARF
extensions to encode Objective C properties, which the debugger can use to let
developers inspect Objective C properties.
</p>
</div>
<!-- *********************************************************************** -->
<h2>
<a name="proposal">Proposal</a>
</h2>
<!-- *********************************************************************** -->
<div>
<p>Objective C properties are always backed by an instance variable. The
instance variables backing properties are identified using
DW_AT_APPLE_property_name attribute. The instance variables with this
attribute may not have data location attributes. The location of instance
variables is determined by debugger only after consulting Objective C runtime.
</p>
<div class="doc_code">
<pre>
@interface I1 {
int n2;
}
@property p1;
@property p2;
@end
@implementation I1
@synthesize p1;
@synthesize p2 = n2;
@end
TAG_structure_type [7] *
AT_APPLE_runtime_class( 0x10 )
AT_name( "I1" )
AT_decl_file( "Objc_Property.m" )
AT_decl_line( 3 )
TAG_member [8]
AT_name( "p1" )
AT_APPLE_property_name(“p1”)
AT_type( {0x00000147} ( int ) )
TAG_member [8]
AT_name( "n2" )
AT_APPLE_property_name(“p2”)
AT_type( {0x00000147} ( int ) )
</pre>
</div>
<p> Developers can decorate a property with attributes which are encoded using
DW_AT_APPLE_property_attribute.
</p>
<div class="doc_code">
<pre>
@property (readonly, nonatomic) int pr;
TAG_member [8]
AT_name(“pr”)
AT_APPLE_property_name(“pr”)
AT_type ( {0x00000147} (int) )
AT_APPLE_property_attribute (DW_APPLE_PROPERTY_readonly, DW_APPLE_PROPERTY_nonatomic)
</pre>
</div>
<p> The setter and getter method names are attached to the property using
DW_AT_APPLE_property_setter and DW_AT_APPLE_property_getter attributes.
</p>
<div class="doc_code">
<pre>
@interface I1
@property (setter=myOwnP3Setter:) int p3;
-(void)myOwnP3Setter:(int)a;
@end
@implementation I1
@synthesize p3;
-(void)myOwnP3Setter:(int)a{ }
@end
0x000003bd: TAG_structure_type [7] *
AT_APPLE_runtime_class( 0x10 )
AT_name( "I1" )
AT_decl_file( "Objc_Property.m" )
AT_decl_line( 3 )
0x000003f3: TAG_member [8]
AT_name( "p3" )
AT_APPLE_property_name(“p3”)
AT_APPLE_property_setter(“myOwnP3Setter:”)
AT_type( {0x00000147} ( int ) )
</pre>
</div>
</div>
<!-- *********************************************************************** -->
<h2>
<a name="newattributes">New DWARF Attributes</a>
</h2>
<!-- *********************************************************************** -->
<div>
<table border="1" cellspacing="0">
<tr>
<th width=200 >Attribute</th>
<th width=200 >Value</th>
<th width=200 >Classes</th>
</tr>
<tr>
<td width=200 >DW_AT_APPLE_property_name</td>
<td width=200 >0x3fe8</td>
<td width=200 >String</td>
</tr>
<tr>
<td width=200 >DW_AT_APPLE_property_getter</td>
<td width=200 >0x3fe9</td>
<td width=200 >String</td>
</tr>
<tr>
<td width=200 >DW_AT_APPLE_property_setter</td>
<td width=200 >0x3fea</td>
<td width=200 >String</td>
</tr>
<tr>
<td width=200 >DW_AT_APPLE_property_attribute</td>
<td width=200 >0x3feb</td>
<td width=200 >Constant</td>
</tr>
</table>
</div>
<!-- *********************************************************************** -->
<h2>
<a name="newconstants">New DWARF Constants</a>
</h2>
<!-- *********************************************************************** -->
<div>
<table border="1" cellspacing="0">
<tr>
<th width=200 >Name</th>
<th width=200 >Value</th>
</tr>
<tr>
<td width=200 >DW_AT_APPLE_PROPERTY_readonly</td>
<td width=200 >0x1</td>
</tr>
<tr>
<td width=200 >DW_AT_APPLE_PROPERTY_readwrite</td>
<td width=200 >0x2</td>
</tr>
<tr>
<td width=200 >DW_AT_APPLE_PROPERTY_assign</td>
<td width=200 >0x4</td>
</tr>
<tr>
<td width=200 >DW_AT_APPLE_PROPERTY_retain</td>
<td width=200 >0x8</td>
</tr>
<tr>
<td width=200 >DW_AT_APPLE_PROPERTY_copy</td>
<td width=200 >0x10</td>
</tr>
<tr>
<td width=200 >DW_AT_APPLE_PROPERTY_nonatomic</td>
<td width=200 >0x20</td>
</tr>
</table>
</div>
<!-- *********************************************************************** -->
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