PLEASE READ ALL OF THIS FILE, ESPECIALLY IF YOU ARE DEFINING A NEW PUBLIC HEADER IN LIBABIGAIL. How symbols that are exported are controlled in libabigail ========================================================== We try to limit the number of ELF symbols that are exported by the libabigail.so shared library. We call this, "symbol visibility control". As GNU/Linux is our development platform, we control symbol visibility by using the visibility support of the G++ compiler. How to do so is properly explained at https://gcc.gnu.org/wiki/Visibility. All symbols are hidden by default ================================= When building translation units that make up the libabigail.so shared library, G++ is invoked with the -fvisibility=hidden directive. Which instructs it to make symbols of functions and global variables *locally* defined in the shared library, *NOT* exported (or global). Exporting symbols of entities declared in public headers ======================================================== In a translation unit that is part of the libabigail.so shared library, before including a header file that is a public libabigail header (e.g, abg-ir.h), one need to declare: #include "abg-internal.h" ABG_BEGIN_EXPORT_DECLARATIONS then all the public header files inclusion (using #include directives) follow. At the end of these public header files inclusion, one need to declare: ABG_END_EXPORT_DECLARATIONS The ABG_BEGIN_EXPORT_DECLARATIONS is a macro defined in abg-internal.h which expands to: #pragma GCC visibility push(default) This instructs G++ to export the symbol of all global functions and variables definitions that are declared from that point on. The ABG_END_EXPORT_DECLARATIONS is a macro defined in abg-internal.h which expands to: #pragma GCC visibility pop It instructs G++ to stop exporting symbols of global functions and variable definition from that point on. In practice, the pair ABG_BEGIN_EXPORT_DECLARATIONS, ABG_END_EXPORT_DECLARATIONS allows us to only export symbols of global functions and variables declared in the block denoted by these two macros. Symbols of anything else that is declared outside of that block are going to be hidden, thanks to the -fvisibility=hidden option passed to G++. So whenever you are defining a new header file with declarations that ought to be part of the API of libabigail, the *definition* file which defines the declarations of the header file must use the ABG_BEGIN_EXPORT_DECLARATIONS and ABG_END_EXPORT_DECLARATIONS macro to include the public header.