When symbol versioning is used in an object, relocations extend the performance of definition testing beyond the simple match of symbol name strings: the version of the reference must also equal the name of the definition. The same index that is used in the symbol table can be referenced in the SHT_GNU_versym section, and the value of this index is then used to acquire name data. The corresponding requirement string is retrieved from the Elfxx_Verneed array, and likewise, the corresponding definition string from the Elfxx_Verdef table.
Bit number 15 of the version symbol controls whether or not the object is hidden; if this bit is set, the object cannot be used and the static linker will ignore the symbol's presence in the object.
Results differ in the interaction of objects that variously use symbol versioning.
The object with the reference and the object with the definitions may both use versioning. All described matching is processed in this case. A fatal error is triggered when no matching definition can be found in the object whose name is the one referenced by the vn_name element in the Elfxx_Verneed entry.
The object with the reference may not use versioning, while the object with the definitions does. In this instance, only the definition with index numbers 1 and 2 will be used in the reference match, the same identified by the static linker as the base definition. In infrequent cases where the static linker was not used, as in calls to dlopen(), a version that does not have the base definition index is acceptable as long as it is the only version for which the symbol is defined.
The object with the reference may use versioning, but the object with the definitions specifies none. A matching symbol is accepted in this case. A fatal error is triggered in the unlikely event that a corruption in the required symbols list obscured an outdated object file and caused a match on the object filename in the Elfxx_Verneed entry.
Finally, both the object with the reference and the object with the definitions may not use versioning. The behavior in this instance defaults to pre-existing symbol rules.