Dynamic loading of the C/COBOL runtime system and the internal routines (partial bind)

When linking with BINDER it is possible to link not the entire C, C++ or
COBOL runtime system and the internal routines but instead simply linkage modules which resolve all open external references to the preloadable components of the CRTE. Unless they are preloaded, the required modules themselves are then not dynamically loaded until runtime.

There are two variants of the partial bind linkage method:

• Standard partial bind

• Complete partial bind

In view of the considerable savings in disk space, it is advisable always to use the partial bind linkage technique when linking the following programs:

• C programs

• COBOL programs

• Programs in other languages which contain components written in C or COBOL or which use common internal routines.

In all cases, CRTE must be installed in the executing system.

• The corresponding CRTE must be available when the program is called.
• If you use shared libraries under POSIX then successful linkage is only guaranteed if you use complete partial bind.

Standard partial bind

When linking with standard partial bind, you should use the library
SYSLNK.CRTE.PARTIAL-BIND instead of SYSLNK.CRTE (see section “Libraries for thepartial bind linkage method on /390 systems”).

In the event of a standard partial bind, the linkage modules loaded from
SYSLNK.CRTE.PARTIAL-BIND resolve all open unresolved references of the object module that is to be linked. Other external references are ignored.

If a loaded module requires runtime system entries that are not needed by the module that has already been loaded and have therefore not been linked then unresolved external references will occur. In such cases, you should use the complete partial bind linkage technique (see “Complete partial bind”).

Depending on the mode (C-Front or ANSI), further libraries are required when linking C++ programs (see the sections “Cfront-C++-library functions and runtime system” and “ANSI-C++ libraries and runtime systems”).

Complete partial bind

When linking using complete partial bind, you should use the library
SYSLNK.CRTE.COMPL instead of SYSLNK.CRTE (see section “Libraries for the partialbind linkage method on /390 systems”).

In the event of a complete partial bind, the loaded linkage modules in
SYSLNK.CRTE.COMPL receive all the entries and external data of the full C or COBOL runtime system. This means that the unresolved external references that may occur in the case of a standard partial bind are excluded when you perform a complete partial bind.

Complete partial bind with C, COBOL and mixed C/COBOL programs

The C and COBOL runtime systems are linked either in their entirety or not at all. This means that:

• If your user program requires at least one C entry then all external references to the entire C runtime system are resolved in the event of a complete partial bind.

• If your COBOL program requires at least one COBOL entry then all external references to the entire COBOL runtime system are resolved in the event of a complete partial bind.

• In the case of pure C programs, no COBOL entries are linked.

• As all entries and all external variables are linked in, they can collide with the entries or external variables of the same name in the application program (duplicate entries). Redefinition of runtime system functions by functions of the same name in the application program is no longer possible, either. Names reserved by the runtime system can be displayed using the following LMS statement:
  //SHOW-ELEMENT (SYSLNK.CRTE.COMPL,*,L),LLM-INF=PAR(INF=ESVD) .

In the case of COBOL and mixed C/COBOL programs the complete partial bind linkage method can only be used if the objects run under POSIX and shared objects are loaded.

Complete partial bind for C++ programs

When binding C++ programs (ANSI), the library SYSLNK.CRTE.CPP-COMPL is also required.

The complete partial bind technique is not supported for C++ programs in Cfront mode.

Special characteristics of complete partial bind

You should remember the following points when linking with SYSLNK.CRTE.COMPL:

• The function _edt is not supported.

• The POSIX and TIME link switches are not present. They are automatically included when you use the cc command under POSIX.

• No upwards compatibility is guaranteed for the extension of the C/C++ systems by new functions in the COMPL libraries. If the application is linked using complete partial bind then each new entry may theoretically generate a conflict with an entry of the same name that is already present in the application.

Employed subsystems

The following subsystems are used for both partial bind variants:

• CRTEPART (for C)

• COBPART (for COBOL)

• CRTESIS (for common routines)

For performance reasons and in order to gain full advantage from the partial bind linkage method, these subsystems should be preloaded.