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Update docs describing objective-c property encoding. This includes support for properties that are not backed by an ivar.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@149879 91177308-0d34-0410-b5e6-96231b3b80d8
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Devang Patel 2012-02-06 18:18:25 +00:00
parent 5a65864f92
commit ba98b6bdd1
1 changed files with 127 additions and 37 deletions
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docs/SourceLevelDebugging.html
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@ -1861,11 +1861,32 @@ developers inspect Objective C properties.
<!-- *********************************************************************** -->
<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 &quot;setter&quot; and &quot;getter&quot; 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 &quot;automatically
synthesized&quot; 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 &quot;dot&quot; 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">
@ -1874,34 +1895,66 @@ variables is determined by debugger only after consulting Objective C runtime.
int n2;
}
@property p1;
@property p2;
@property int p1;
@property int 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>
This produces the following DWARF (this is a &quot;pseudo dwarfdump&quot; 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>
@ -1909,11 +1962,15 @@ DW_AT_APPLE_property_attribute.
<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>
@ -1933,22 +1990,55 @@ DW_AT_APPLE_property_setter and DW_AT_APPLE_property_getter attributes.
@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>
@ -1963,9 +2053,9 @@ DW_AT_APPLE_property_setter and DW_AT_APPLE_property_getter attributes.
<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>