OT Bytecode Attributes/CallinFlags

Attribute CallinFlags

Intent

The CallinFlags attribute is a fixed-length attribute used in the attributes table of method_info structures.

Location:

A role method or a callin wrapper or a base call surrogate (for return type).

Content:

An integer encoding the callin flags.

Purpose:

• Used by OTRE:

CALLIN_FLAG_OVERRIDING

CALLIN_FLAG_WRAPPER

The OTRE uses this information to realize the inheritance of method bindings.

(OTRE internal: This flag prevents the OTRE from generating an empty base-call-surrogate which would wrongly override an inherited (non-empty) version.)

• The other flags are only used by the compiler.

CALLIN_FLAG_BASE_SUPER_CALL: OTRE part is handled via OTSpecialAccess attribute (kind SUPER_METHOD_ACCESS).

Format:

   CallinFlags {
     u2 attribute_name_index;
     u4 attribute_length;
     u2 callin_flags;
    } 

The items of the CallinFlags structure are as follows:

• attribute_name_index

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

• attribute_length

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

• callin_flags

The value of the callin_flags item is a mask of flags (used to denote ...). The interpretation of each flag, when set, is as shown in the following:

Flag Name	Value	Interpretation
CALLIN_FLAG_OVERRIDING	1	this method is overriding an inherited version
CALLIN_FLAG_WRAPPER	2	this method is the generated team-level callin wrapper
CALLIN_FLAG_DEFINITELY_MISSING_BASECALL	8	for base call flow analysis including super calls
CALLIN_FLAG_POTENTIALLY_MISSING_BASECALL	16	for base call flow analysis including super calls
CALLIN_FLAG_BASE_SUPER_CALL	32	is the base call targeting the base's super?
CALLIN_RETURN_MASK	bits 9-12	encoding of original non-reference return type, see IOTConstants.CALLIN_RETURN_VOID ff..