From ba98b6bdd10e2454294255897529c239a41dece1 Mon Sep 17 00:00:00 2001 From: Devang Patel Date: Mon, 6 Feb 2012 18:18:25 +0000 Subject: [PATCH] Update docs describing objective-c property encoding. This includes support for properties that are not backed by an ivar. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@149879 91177308-0d34-0410-b5e6-96231b3b80d8 --- docs/SourceLevelDebugging.html | 164 +++++++++++++++++++++++++-------- 1 file changed, 127 insertions(+), 37 deletions(-) diff --git a/docs/SourceLevelDebugging.html b/docs/SourceLevelDebugging.html index 0d2d3f49965..e5f982d3f5e 100644 --- a/docs/SourceLevelDebugging.html +++ b/docs/SourceLevelDebugging.html @@ -1861,11 +1861,32 @@ developers inspect Objective C properties.
-

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. +

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. +

+

+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. +

+

+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. +

+

+The following examples will serve as illustration for our discussion:

@@ -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 ) )
+

+This produces the following DWARF (this is a "pseudo dwarfdump" output): +

+
+
+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 ) )
+
+
+ +

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. +

+ +

+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. +

+

Developers can decorate a property with attributes which are encoded using DW_AT_APPLE_property_attribute.

@@ -1909,11 +1962,15 @@ DW_AT_APPLE_property_attribute. 
 @property (readonly, nonatomic) int pr;
-
-
-TAG_member [8] 
-  AT_name(“pr”) 
-  AT_APPLE_property_name(“pr”) 
+
+
+

+Which produces a property tag: +

+

+
+TAG_APPLE_property [8] 
+  AT_name( "pr" ) 
   AT_type ( {0x00000147} (int) ) 
   AT_APPLE_property_attribute (DW_APPLE_PROPERTY_readonly, DW_APPLE_PROPERTY_nonatomic)
@@ -1933,22 +1990,55 @@ DW_AT_APPLE_property_setter and DW_AT_APPLE_property_getter attributes. @synthesize p3; -(void)myOwnP3Setter:(int)a{ } @end + +
+

+The DWARF for this would be: +

+
+
 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 )
+ +

+ New DWARF Tags +

+ + +
+ + + + + + + + + +
TAGValue
DW_TAG_APPLE_property0x4200
+ +
+

New DWARF Attributes @@ -1963,9 +2053,9 @@ DW_AT_APPLE_property_setter and DW_AT_APPLE_property_getter attributes. Classes - DW_AT_APPLE_property_name - 0x3fe8 - String + DW_AT_APPLE_property + 0x3fed + Reference DW_AT_APPLE_property_getter