#include <dlfcn.h>

If an error occurs when calling shared library management routines, the system error variable errno is set to an appropriate error value. Constants are defined for these error values in /usr/include/errno.h (see errno(2)). Thus, if a program checks for these error values, it must include errno.h:

#include <errno.h>

Throughout this section, all examples are given in C. To learn how to call these routines from aC++ or Fortran, see the inter-language calling conventions described in the compiler documentation.

Using Shared Libraries with cc and ld Options

In IPF/PA-64 mode, you can access the shl_load and dlopen routines by specifying either -ldldor -ldlon the command line. In PA-32 mode, you can access theshl_load family of routines by specifying the -ldldoption on the cc(1) or ld(1) command line. The default behavior of the PA-64 and IPF linker is to export all symbols defined by a program. However, some PA-32 implementations do not, by default, export all symbols, instead exporting only those symbols imported by a shared library seen at link time. In PA-32 compatibility mode, use the -Eoption to ld to ensure that all symbols defined in the program are available to the loaded libraries. To create shared libraries, compile source files with +z or +Z and link the resultant object files. In PA-32 mode, to create share libraries, compile source files with +Z or +Z and link the resultant object files with -b.

Initializers for Shared Libraries

A shared library can have an initialization routine - known as an initializer - that is called when the load module (a shared library or executable) is loaded (initializer) or explicitly unloaded (finalizer or terminator). Typically, an initializer is used to initialize a shared library's data when the library is loaded. When a program begins execution, its initializers are called before any other user code is executed. This allows for setup at initialization and cleanup at termination. Also, when a shared library is explicitly loaded using shl_load or dlopen or unloaded using shl_unload or dlclose, its initializers and terminators are called at the appropriate time. In IPF/PA-64 mode, you can specify initializers and terminators even for archive libraries or nonshared executables.

Styles of Initializers

The linker supports two different types of initializers and terminators:

•Init/fini style. (Not supported in HP-UX 10.X)

•HP-UX 10.X style.

Init/Fini Style Initializers

This style uses init and fini functions to handle initialization and finalization (terminator) operations. Init Initializers (inits) are called before the user's code starts or when a shared library is loaded. Functions specified with this option must not take arguments and return nothing (void functions). The C compiler pragma "init" can be used to declare these functions. For example:

#pragma init "my_init"

void my_init() { ... do some initializations ... }

The ld command also supports the +init function option to specify the initializer. Use this option while building a shared library, an incomplete executable, or fully bound executable. Use the +init option to specify the initializer functions, to be invoked in reverse order, the order the functions appear right to left on the command line. Initializers are called in depth-first order. For example, when a shared library is loaded, the initializers in all its dependent libraries are called first. Do not use +init with the -roption. (The linker ignores the +init option.) You can specify more than one initializer function on the command line with multiple option-symbol pairs, that is, each function you specify must be preceded by the +init option.

138 Shared Library Management Routines