On Thu, 2016-10-13 at 18:12 +0200, Pierre-Marie de Rodat wrote: > Currently, the DWARF description does not specify the signedness of the > representation of enumeration types. This is a problem in some > contexts where DWARF consumers need to determine if value X is greater > than value Y. > > For instance in Ada: > > type Enum_Type is ( A, B, C, D); > for Enum_Type use (-1, 0, 1, 2); > > type Rec_Type (E : Enum_Type) is record > when A .. B => null; > when others => B : Booleann; > end record; > > The above can be described in DWARF the following way: > > DW_TAG_enumeration_type(Enum_Type) > | DW_AT_byte_size: 1 > DW_TAG_enumerator(A) > | DW_AT_const_value: -1 > DW_TAG_enumerator(B) > | DW_AT_const_value: 0 > DW_TAG_enumerator(C) > | DW_AT_const_value: 1 > DW_TAG_enumerator(D) > | DW_AT_const_value: 2 > > DW_TAG_structure_type(Rec_Type) > DW_TAG_member(E) > | DW_AT_type: <Enum_Type> > DW_TAG_variant_part > | DW_AT_discr: <E> > DW_TAG_variant > | DW_AT_discr_list: DW_DSC_range 0x7f 0 > DW_TAG_variant > | DW_TAG_member(b) > > DWARF consumers need to know that enumerators (A, B, C and D) are signed > in order to determine the set of E values for which Rec_Type has a B > field. In practice, they need to know how to interpret the 0x7f LEB128 > number above (-1, not 127). > > There seems to be only two alternatives to solve this issue: one is to > add a DW_AT_type attribute to DW_TAG_enumerator_type DIEs to make it > point to a base type that specifies the signedness. The other is to > make sure the form of the DW_AT_const_value attribute carries the > signedness information. This patch implements the latter.
IMHO having an explicit DW_AT_type pointing at the base type with size and encoding for the DW_TAG_enumerator_type is better for consumers than having to try and interpret the DW_FORM used to encode the values. Alternatively could we just attach a DW_AT_encoding to the DW_TAG_enumeration_type? The spec doesn't list it as one of the attributes for an enumeration_type, but it makes sense given it already carries bit/byte size attributes. Thanks, Mark
