Following are the commands you can use to create a shared library called libunits.so:

$ cc -Aa -c +z length.c volume.c mass.c

$ ld -b -o libunits.so length.o volume.o mass.o

Other topics relevant to shared libraries are:

•“Shared Library Dependencies” (page 100)

•“Updating a Shared Library” (page 102)

•“Shared Library Location (IPF)” (page 102)

•“Improving Shared Library Performance” (page 102)

•“Function Level Versioning” (page 110)

Creating Position-Independent Code (PIC)

In PA-32 mode, the first step in creating a shared library is to create object files containing position-independent code (PIC). There are two ways to create PIC object files:

•Compile source files with the +z or +Z compiler option, described below.

•Write assembly language programs that use appropriate addressing modes, described in “Writing and Generating Position-Independent Code” (page 185) .

In PA-32 mode, the +z and +Z options force the compiler to generate PIC object files. In PA-64 and IPF mode, the +Z option is the default.

Example Using +z

Suppose you have some C functions, stored in length.c, that convert between English and Metric length units. To compile these routines and create PIC object files with the C compiler, you can use this command:

$ cc -Aa -c +z length.c

The +z option creates PIC.

You can then link it with other PIC object files to create a shared library, as discussed in “Creating the Shared Library with ld” (page 99) .

Comparing +z and +Z

In PA-32 mode, the +z and +Z options are essentially the same. Normally, you compile with +z. However, in some instances - when the number of referenced symbols per shared library exceeds a predetermined limit - you must recompile with the +Z option instead. In this situation, the linker displays an error message and tells you to recompile the library with +Z.

In PA-64 and IPF mode, +Z is the default and the compilers ignore the options and generate PIC code.

Compiler Support for +z and +Z

In PA-32 mode, the C, C++, FORTRAN, and Pascal compilers support the +z and +Z options.

In PA-64 and IPF mode, +Z is the default for the C and C++ compilers.

Creating the Shared Library with ld

To create a shared library from one or more PIC object files, use the linker, ld, with the -boption. By default, ld names the library a.out. You can change the name with the -ooption.

For example, suppose you have three C source files containing routines to do length, volume, and mass unit conversions. They are named length.c, volume.c, and mass.c, respectively. To make a shared library from these source files, first compile all three files, then combine the resulting

.o files with ld. Following are the commands you can use to create a shared library named libunits.so:

Creating Shared Libraries 99