<!-- *********************************************************************** -->
<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>Objective C properties exist separately from class members. A property
+can be defined only by "setter" and "getter" selectors, and
+be calculated anew on each access. Or a property can just be a direct access
+to some declared ivar. Finally it can have an ivar "automatically
+synthesized" for it by the compiler, in which case the property can be
+referred to in user code directly using the standard C dereference syntax as
+well as through the property "dot" syntax, but there is no entry in
+the @interface declaration corresponding to this ivar.
+</p>
+<p>
+To facilitate debugging, these properties we will add a new DWARF TAG into the
+DW_TAG_structure_type definition for the class to hold the description of a
+given property, and a set of DWARF attributes that provide said description.
+The property tag will also contain the name and declared type of the property.
+</p>
+<p>
+If there is a related ivar, there will also be a DWARF property attribute placed
+in the DW_TAG_member DIE for that ivar referring back to the property TAG for
+that property. And in the case where the compiler synthesizes the ivar directly,
+the compiler is expected to generate a DW_TAG_member for that ivar (with the
+DW_AT_artificial set to 1), whose name will be the name used to access this
+ivar directly in code, and with the property attribute pointing back to the
+property it is backing.
+</p>
+<p>
+The following examples will serve as illustration for our discussion:
</p>
<div class="doc_code">
int n2;
}
-@property p1;
-@property p2;
+@property int p1;
+@property int p2;
@end
@implementation I1
@synthesize p1;
@synthesize p2 = n2;
@end
+</pre>
+</div>
-
-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 ) )
+<p>
+This produces the following DWARF (this is a "pseudo dwarfdump" output):
+</p>
+<div class="doc_code">
+<pre>
+0x00000100: TAG_structure_type [7] *
+ AT_APPLE_runtime_class( 0x10 )
+ AT_name( "I1" )
+ AT_decl_file( "Objc_Property.m" )
+ AT_decl_line( 3 )
+
+0x00000110 TAG_APPLE_property
+ AT_name ( "p1" )
+ AT_type ( {0x00000150} ( int ) )
+
+0x00000120: TAG_APPLE_property
+ AT_name ( "p2" )
+ AT_type ( {0x00000150} ( int ) )
+
+0x00000130: TAG_member [8]
+ AT_name( "_p1" )
+ AT_APPLE_property ( {0x00000110} "p1" )
+ AT_type( {0x00000150} ( int ) )
+ AT_artificial ( 0x1 )
+
+0x00000140: TAG_member [8]
+ AT_name( "n2" )
+ AT_APPLE_property ( {0x00000120} "p2" )
+ AT_type( {0x00000150} ( int ) )
+
+0x00000150: AT_type( ( int ) )
</pre>
</div>
+<p> Note, the current convention is that the name of the ivar for an
+auto-synthesized property is the name of the property from which it derives with
+an underscore prepended, as is shown in the example.
+But we actually don't need to know this convention, since we are given the name
+of the ivar directly.
+</p>
+
+<p>
+Also, it is common practice in ObjC to have different property declarations in
+the @interface and @implementation - e.g. to provide a read-only property in
+the interface,and a read-write interface in the implementation. In that case,
+the compiler should emit whichever property declaration will be in force in the
+current translation unit.
+</p>
+
<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”)
+</pre>
+</div>
+<p>
+Which produces a property tag:
+<p>
+<div class="doc_code">
+<pre>
+TAG_APPLE_property [8]
+ AT_name( "pr" )
AT_type ( {0x00000147} (int) )
AT_APPLE_property_attribute (DW_APPLE_PROPERTY_readonly, DW_APPLE_PROPERTY_nonatomic)
</pre>
@synthesize p3;
-(void)myOwnP3Setter:(int)a{ }
@end
+</pre>
+</div>
+<p>
+The DWARF for this would be:
+</p>
+<div class="doc_code">
+<pre>
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 ) )
+
+0x000003cd TAG_APPLE_property
+ AT_name ( "p3" )
+ AT_APPLE_property_setter ( "myOwnP3Setter:" )
+ AT_type( {0x00000147} ( int ) )
+
+0x000003f3: TAG_member [8]
+ AT_name( "_p3" )
+ AT_type ( {0x00000147} ( int ) )
+ AT_APPLE_property ( {0x000003cd} )
+ AT_artificial ( 0x1 )
</pre>
</div>
</div>
+<!-- *********************************************************************** -->
+<h4>
+ <a name="objcpropertynewtags">New DWARF Tags</a>
+</h4>
+<!-- *********************************************************************** -->
+
+<div>
+<table border="1" cellspacing="0">
+ <tr>
+ <th width=200 >TAG</th>
+ <th width=200 >Value</th>
+ </tr>
+ <tr>
+ <td width=200 >DW_TAG_APPLE_property</td>
+ <td width=200 >0x4200</td>
+ </tr>
+</table>
+
+</div>
+
<!-- *********************************************************************** -->
<h4>
<a name="objcpropertynewattributes">New DWARF Attributes</a>
<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>
+ <td width=200 >DW_AT_APPLE_property</td>
+ <td width=200 >0x3fed</td>
+ <td width=200 >Reference</td>
</tr>
<tr>
<td width=200 >DW_AT_APPLE_property_getter</td>
projects / oota-llvm.git / blobdiff