18.3.2 Building a Stand-alone Library

GNAT's Project facility provides a simple way of building and installing stand-alone libraries; see Stand-alone Library Projects. To be a Stand-alone Library Project, in addition to the two attributes that make a project a Library Project (Library_Name and Library_Dir; see Library Projects), the attribute Library_Interface must be defined. For example:

        for Library_Dir use "lib_dir";
        for Library_Name use "dummy";
        for Library_Interface use ("int1", "int1.child");

Attribute Library_Interface has a non-empty string list value, each string in the list designating a unit contained in an immediate source of the project file.

When a Stand-alone Library is built, first the binder is invoked to build a package whose name depends on the library name (b~dummy.ads/b in the example above). This binder-generated package includes initialization and finalization procedures whose names depend on the library name (dummyinit and dummyfinal in the example above). The object corresponding to this package is included in the library.

You must ensure timely (e.g., prior to any use of interfaces in the SAL) calling of these procedures if a static SAL is built, or if a shared SAL is built with the project-level attribute Library_Auto_Init set to "false".

For a Stand-Alone Library, only the ALI files of the Interface Units (those that are listed in attribute Library_Interface) are copied to the Library Directory. As a consequence, only the Interface Units may be imported from Ada units outside of the library. If other units are imported, the binding phase will fail.

It is also possible to build an encapsulated library where not only the code to elaborate and finalize the library is embedded but also ensuring that the library is linked only against static libraries. So an encapsulated library only depends on system libraries, all other code, including the GNAT runtime, is embedded. To build an encapsulated library the attribute Library_Standalone must be set to encapsulated:

        for Library_Dir use "lib_dir";
        for Library_Name use "dummy";
        for Library_Kind use "dynamic";
        for Library_Interface use ("int1", "int1.child");
        for Library_Standalone use "encapsulated";

The default value for this attribute is standard in which case a stand-alone library is built.

The attribute Library_Src_Dir may be specified for a Stand-Alone Library. Library_Src_Dir is a simple attribute that has a single string value. Its value must be the path (absolute or relative to the project directory) of an existing directory. This directory cannot be the object directory or one of the source directories, but it can be the same as the library directory. The sources of the Interface Units of the library that are needed by an Ada client of the library will be copied to the designated directory, called the Interface Copy directory. These sources include the specs of the Interface Units, but they may also include bodies and subunits, when pragmas Inline or Inline_Always are used, or when there is a generic unit in the spec. Before the sources are copied to the Interface Copy directory, an attempt is made to delete all files in the Interface Copy directory.

Building stand-alone libraries by hand is somewhat tedious, but for those occasions when it is necessary here are the steps that you need to perform:

• Compile all library sources.
• Invoke the binder with the switch -n (No Ada main program), with all the ALI files of the interfaces, and with the switch -L to give specific names to the init and final procedures. For example:

              gnatbind -n int1.ali int2.ali -Lsal1
  

• Compile the binder generated file:

              gcc -c b~int2.adb
  

• Link the dynamic library with all the necessary object files, indicating to the linker the names of the init (and possibly final) procedures for automatic initialization (and finalization). The built library should be placed in a directory different from the object directory.
• Copy the ALI files of the interface to the library directory, add in this copy an indication that it is an interface to a SAL (i.e., add a word SL on the line in the ALI file that starts with letter “P”) and make the modified copy of the ALI file read-only.

Using SALs is not different from using other libraries (see Using a library).