no OID field in OLD or NEW records inside trigger functions?

This trigger function attempts to copy a record into an archive table
before deletion:

create trigger archive_adresse before update or delete on adresse
for each row execute procedure archive_row();

create function archive_row() returns opaque as '
DECLARE
tname text;
rec RECORD;
BEGIN
tname := TG_RELNAME || ''_archive'';
INSERT INTO tname SELECT * from TG_RELNAME WHERE oid = OLD.oid;
RETURN OLD;
END;
' language 'plpgsql';

But I get:
psql:archive.sql:25: ERROR: record old has no field oid

What would the best way to have a generic trigger function copy an
entire NEW or OLD row to an archive (given that the archive table is
always named <table>_archive)?

Thanks in advance,

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