z/OS V1R9.0 UNIX System Services Command ... - Christian Grothoff

c89, cc, and c++
78 z/OS V1R9.0 UNIX System Services Command Reference
DLL (Dynamic Link Library)
A DLL is a part of a program that is not statically bound to the
program. Instead, linkage to symbols (variables and functions) is
completed dynamically at execution time. DLLs can improve
storage utilization, because the program can be broken into smaller
parts, and some parts may not always need to be loaded. DLLs can
improve maintainability, because the individual parts can be
managed and serviced separately.
In order to create a DLL, some symbols must be identified as being
exported for use by other parts of the program. This can be done
with the z/OS XL C/C++ #pragma export compiler directive, or by
using the z/OS XL C/C++ EXPORTALL compiler option. If during
the link-editing phase some of the parts have exported symbols, the
executable which is created is a DLL. In addition to the DLL, a
definition side-deck is created, containing link-editing phase
IMPORT control statements which name those symbols which were
exported by the DLL. In order for the definition side-deck to be
created, the DLL link editor option must be specified. This definition
side-deck is subsequently used during the link-editing phase of a
program which is to use the DLL. See the file.x operand under
Operands on page 83 for information on where the definition
side-deck is written. In order for the program to refer to symbols
exported by the DLL, it must be compiled with the DLL compiler
option.
Example: To compile and link a program into a DLL, you could
specify:
c89 -o outdll -W c,exportall -W l,dll file.c
To subsequently use file.x definition side-decks, specify them along
with any other file.o object files specified for c89/cc/c++ link-editing
phase.
Example: To accomplish this task, you could specify:
c89 –o myappl –W c,dll myappl.c outdll.x
In order to run an application which is link-edited with a definition
side-deck, the DLL must be made available (the definition side-deck
created along with the DLL is not needed at execution time). When
the DLL resides in the z/OS UNIX file system, it must be in either
the working directory or in a directory named on the LIBPATH
environment variable. Otherwise it must be a member of a data set
in the search order used for MVS programs.
Note: For non-DLL C++ compiles, a dummy definition side file will
be allocated to prevent the binder from issuing a warning
message. If you do want the binder to issue a warning
message when an exported symbol is encountered, specify
the DLL=NO option for the link-editing phase; for example:
c++ -o outfile -W l,dll=no file.C
IPA (interprocedural analysis)
IPA optimization is independent from and can be used in addition to
the c89/cc/c++ optimization level options (such as –O). IPA
optimization can also improve the execution time of your
application. IPA is a mechanism for performing optimizations across