OT Bytecode Attributes/CallinMethodMappings

Attribute CallinMethodMappings

Intent

The CallinMethodMappings attribute is a variable-length attribute used in the attributes table of the ClassFile structure.

Location:

A bound role class with a callin binding.

Content:

A list of method bindings. For structure, see below.

Purpose:

The OTRE uses this attribute to determine

• a) which callins (callin wrapper calls) have to be woven into which base methods
• b) which base method has to be called while generating a base-call in a callin role method

Format:

   CallinMethodMappings {
     u2 attribute_name_index;
     u4 attribute_length;
     u2 method_mappings_count;
     CallinMethodMapping method_mappings[method_mappings_count];
    }
 
    CallinMethodMapping {
     u2 binding_file_name;
     u2 binding_line_number;
     u2 binding_line_offset;
     u2 binding_label;
     u2 role_method_name_index;
     u2 role_method_signatur_index;
     u2 flags;
     u2 lift_method_name;
     u2 lift_method_signature;
     u2 binding_modifier;
     u2 base_method_mapping_count;
     BaseMethodMapping base_mappings[base_method_mapping_count];
    }
   
    BaseMethodMapping {
     u2 base_method_name_index;
     u2 base_method_signature_index;
     u2 wrapper_name_index;
     u2 wrapper_signature_index;
     u1 base_flags;
     u4 translation_flags;
    }   

The items of the CallinMethodMappings structure are as follows:

• attribute_name_index

The constant_pool entry at that index must be a CONSTANT_Utf8_info representing the string "CallinRoleBaseBindings".

• attribute_length

The value of the attribute_length item indicates the length of the attribute, excluding the initial six bytes.

• method_mappings_count

The value of the method_mappings_count item indicates the number of entries in the method_mappings array.

• method_mappings[]

Each pair role method RM + bound base method BM are listed here. Each method_mappings array entry contains the following 12 items:

• binding_file_name

The constant_pool index representing the name of the file which contains the callin binding.

• binding_line_number

The line number of the callin binding.

• binding_line_offset

The line number offset of the callin binding.

• binding_label

The constant_pool index representing the binding label.

• role_method_name_index

The constant_pool index representing the name of RM.

• role_method_signatur_index

The constant_pool index representing the signature of RM as type descriptor.

The signature is "retrenched", i.e., it does not contain the enhancement arguments [Team;[IIII[Object;, but other than that erasures are used to reflect the byte-code level signature

• flags

The value of the flags item is a mask of flags. The interpretation of each flag, when set, is as shown in the following:

Flag Name	Value	Interpretation
STATIC_ROLE_METHOD	1	the bound role method is static
QUERY	2	removed
INHERITED	4	the bound role method is inherited (not used by the OTRE)
COVARIANT_BASE_RETURN	8	the callin binding may capture base methods with covariant return types

• lift_method_name

The constant_pool index representing the name of the lift method for the result ("", if no lifting necessary)

• lift_method_signature

The constant_pool index representing the signature of the lift method for the result ("", if no lifting necessary)

• binding_modifier

The constant_pool index representing the binding modifier ("after", "before" or "replace").

• base_method_mapping_count

The value of the base_method_mapping_count item indicates the number of entries in the base_mappings array.

• base_mappings[]

Each base_mappings array entry contains the following six items:

• base_method_name_index

The constant_pool index representing the name of BM.

• base_method_signature_index

The constant_pool index representing the signature of BM as type descriptor.

The descriptor uses erasures as to reflect the byte-code level signature

• wrapper_name_index

The constant_pool index representing the name of the callin wrapper for the pair RM + BM.

• wrapper_signature_index

The constant_pool index representing the signature of the callin wrapper for the pair RM + BM as type descriptor.

• base_flags

The value of the base_flags item is a mask of flags. The interpretation of each flag, when set, is as shown in the following:

Flag Name	Value	Interpretation
CALLIN	1	the bound base method is a callin (role) method
STATIC_BASE_METHOD	2	the bound base method is static

• translation_flags

here the compiler encodes with arguments/return values require translation (lifting/lowering) to be performed by the callin wrapper

the OTRE uses this to determine when a base-call result requires lifting