Symbol Visibility

Controlling symbol visibility for executables and dynamic libraries allows to reduce the sets of symbols exported by them to what is actually necessary. Today, all relevant C/C++ compilers have (slightly different) syntax extensions to control in the C/C++ source code the set of exported symbols. The following describes how to enable these visibility features for a given executable or dynamic library X in the OOo code base:

• In all the makefile.mks where C/C++ source code belonging to X is compiled or where X (or part of X) is linked, VISIBILITY_HIDDEN=TRUE must be declared. (It is an error to have that declaration in makefile.mks completely or partially controlling other stuff.)
• If none of the symbols that shall be exported by X are declared in a header file that is used by code outside X (e.g., if X is a dynamic library that is a UNO component and only exports component_getFactory, component_getImplementationEnvironment, component_writeInfo):
  • Annotate the definitions of those entities (functions, classes) in the C/C++ source code that correspond to those symbols with SAL_DLLPUBLIC_EXPORT.
• If, however, there are symbols that shall be exported by X and that are declared in a header file that is used by code outside X:
  • Chose a unique (all lowercase) token t to represent X.
  • In all the makefile.mks where C/C++ source code defining one of those symbols is compiled, CDEFS+=-DOOO_DLLIMPLEMENTATION_T must be declared (where T is the all uppercase equivalent of t). (It is an error to have that declaration in makefile.mks completely or partially controlling other stuff.)
  • Create a header file tdllapi.h resp. tdllapi.hxx that contains

    #include "sal/types.h"
    

#if defined OOO_DLLIMPLEMENTATION_<var>T</var> #define OOO_DLLPUBLIC_<var>T</var> SAL_DLLPUBLIC_EXPORT #else #define OOO_DLLPUBLIC_<var>T</var> SAL_DLLPUBLIC_IMPORT #endif