8.4.14 Hiding Symbols

Symbol hiding prevents the symbol from being listed in the output file's symbol table. While localization is used to prevent name space clashes in a link unit (see Section 8.4.16), symbol hiding is used to obscure symbols which should not be visible outside a link unit. Such symbol’s names appear only as empty strings or “no name” in object file readers. The linker supports symbol hiding through the --hide and --unhide options.

The syntax for these options are:

--hide='pattern'

--unhide='pattern'

The pattern is a "glob" (a string with optional ? or * wildcards). Use ? to match a single character. Use * to match zero or more characters.

The --hide option hides global symbols with a linkname matching the pattern. It hides symbols matching the pattern by changing the name to an empty string. A global symbol that is hidden is also localized.

The --unhide option reveals (un-hides) global symbols that match the pattern that are hidden by the --hide option. The --unhide option excludes symbols that match pattern from symbol hiding provided the pattern defined by --unhide is more restrictive than the pattern defined by --hide.

These options have the following properties:

• The --hide and --unhide options can be specified more than once on the command line.
• The order of --hide and --unhide has no significance.
• A symbol is matched by only one pattern defined by either --hide or --unhide.
• A symbol is matched by the most restrictive pattern. Pattern A is considered more restrictive than Pattern B, if Pattern A matches a narrower set than Pattern B.
• It is an error if a symbol matches patterns from --hide and --unhide and one does not supersede the other. Pattern A supersedes pattern B if A can match everything B can and more. If Pattern A supersedes Pattern B, then Pattern B is said to more restrictive than Pattern A.
• These options affect final and partial linking.

In map files these symbols are listed under the Hidden Symbols heading.